| 1. |
- Forsberg, Viviane, 1981-, et al.
(författare)
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Photodetector of multilayer exfoliated MoS2 deposited on polyimide films
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We fabricated a photodetector based on multilayer molybdenum disulfide (MoS2) by micromechanical cleavage of a molybdenite crystal using a polyimide film. We deposited 40 nm of gold by vacuum sputtering and copper tape was used for the contacts. Without any surface treatment, we achieved high responsivity at different incident optical power. The calculated responsivity was 23 mA/W of incident optical power in the range between 400 and 800 nm. For the responsivity measurement it was estimated that MoS2 have a bandgap of 1.6 eV, which lies between monolayer and multilayer films. The thickness of the MoS2 thin film was determined by Raman spectroscopy evaluating the difference between the in plane and out of plane Raman modes. The measurement of IV curves indicated Ohmic contacts in respect to the Au regardless of the incident optical power. Our device fabrication was much simpler than previous reported devices and can be used to test the light absorption and luminescence capabilities of exfoliated MoS2.
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| 2. |
- Balliu, Enkeleda, et al.
(författare)
-
Laser sintering of silver nano-particles inks printed on paper substrates
- 2015
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781628414417 ; , s. Art. no. 935112-
-
Konferensbidrag (refereegranskat)abstract
- In this work we have investigated the use of laser sintering of different ink-jet printed nano-particle inks (NPIs) on paper substrates. Laser sintering is shown to offer a fast and non-destructive way to produce paper based printed electronics. A continuous wave fiber laser source at 1064 nm is used and evaluated in combination with a galvo-scanning mirror system. A conductivity in order of 2.16 ∗ 107 S/m is reached for the silver NPI structures corresponding to nearly 35 % conductivity compared to that of bulk silver and this is achieved without any observable damage to the paper substrate. © 2015 SPIE.
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| 3. |
- Bond, Luke, et al.
(författare)
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Electrically conductive polymer-graphene composite material for selective laser sintering additive manufacturing
- 2024
-
Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE - The International Society for Optics and Photonics. - 9781510670068
-
Konferensbidrag (refereegranskat)abstract
- Additive manufacturing is rapidly growing, where selective laser sintering technology dominates for industrial use. In the case of polymer selective laser sintering, polyamide is the standard material. However, polyamide is an electrical insulator, and for specific applications, it would be desirable to be able to manufacture polymer-based electrically conductive parts. Electromagnetic Compatibility is one of the most significant targeted applications, where the introduction of electric vehicles raises new electromagnetic compatibility demands. The goal is, therefore, to develop an electrically conductive composite material for selective laser sintering using graphene as the additive. Composites are prepared by mixing polyamide, graphene, and additives with varying graphene/polyamide ratios. The aim of this investigation is the laser-assisted processing of the resulting graphene/polyamide composites with various parameters to sinter the material, forming a solid conductive structure. The structure is characterized using SEM and resistance measurements. Results show sheet resistance values of about 700Ω/sq after laser-assisted processing with good powder flowability.
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| 4. |
- Zhang, Renyun, et al.
(författare)
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High-performance transparent and flexible electrodes made by flash-light sintering of gold nanoparticles
- 2018
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:12, s. 7191-7198
-
Tidskriftsartikel (refereegranskat)abstract
- Metallic nanowire-based transparent electrodes (TEs) are potential alternatives to indium tin oxide (ITO). To achieve a high performance [sheet resistance (Rs) < 100 Ω/sq, transmittance (T%) > 90%], the nanowires must have a high length-to-diameter (L/D) ratio to minimize the number of wire-to-wire junctions. Attempts to produce TEs with gold nanowires have been made, and the results reveal difficulties in achieving the requirements. A successful strategy involves creating templated gold nanonetworks through multiple procedures. Here, we present a simple and efficient method that uses flash-light sintering of a gold nanonetwork film into gold TEs (Rs: 82.9 Ω/sq, T %: 91.79%) on a thin polycarbonate film (25 μm). The produced gold TEs have excellent mechanical, electrical, optical, and chemical stabilities. Mechanisms of the formation of gold nanonetworks and the effect of flash-light have been analyzed. Our findings provide a scalable process for producing transparent and flexible gold electrodes with a total processing time of less than 8 min without the use of heating, vacuum processing, and organic chemicals and without any material loss. This is possible because all the gold nanoparticles have been aggregated and filtrated on the filter membranes. The area density of gold is 0.094 g/m2 leading low material costs, which is very competitive with the price of commercial TEs.
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| 5. |
- Zhang, Renyun, et al.
(författare)
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Photoconductivity of acid exfoliated and flash-light-processed MoS2 films
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- MoS2 has been studied intensively during recent years as a semiconducting material in several fields, including optoelectronics, for applications such as solar cells and phototransistors. The photoresponse mechanisms of MoS2 have been discussed but are not fully understood, especially the phenomenon in which the photocurrent slowly increases. Here, we report on a study of the photoresponse flash-light-processed MoS2 films of different thicknesses and areas. The photoresponse of such films under different light intensities and bias voltages was measured, showing significant current changes with a quick response followed by a slow one upon exposure to pulsed light. Our in-depth study suggested that the slow response was due to the photothermal effect that heats the MoS2; this hypothesis was supported by the resistivity change at different temperatures. The results obtained from MoS2 films with various thicknesses indicated that the minority-carrier diffusion length was 1.36 mu m. This study explained the mechanism of the slow response of the MoS2 film and determined the effective thickness of MoS2 for a photoresponse to occur. The method used here for fabricating MoS2 films could be used for fabricating optoelectronic devices due to its simplicity.
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| 6. |
- Zhang, Renyun, et al.
(författare)
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Sensing body motions based on charges generated on the body
- 2019
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 63
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Tidskriftsartikel (refereegranskat)abstract
- The sensing of body motions is of great importance in areas such as healthcare, rehabilitation, and human-computer interactions. Different methods have been developed based on visual or electrical signals. However, such signals are acquired by external devices and are not intrinsic signals that are created on the body. Here, we report a new universal body motion sensor (UBS) to detect motions based on the intrinsic contact electrification (CE) of the skin or electrical induction (EI) of the body. The CE or EI generates charges on the body, leading to potential differences between the body and ground that can be measured to identify different body motions, such as motions of the head, arms, fingers, waist, legs, feet and toes. Proof-of-concept experiments have demonstrated that the UBS can be used to monitor the conditions of people with Parkinson's disease (PD) and to quantitatively monitor the recovery of those with a leg injury, suggesting great potential for healthcare applications.
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| 7. |
- Andersson, Henrik, Dr, 1975-, et al.
(författare)
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PEDOT : PSS thermoelectric generators printed on paper substrates
- 2019
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Ingår i: Journal of Low Power Electronics and Applications. - : MDPI AG. - 2079-9268. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Flexible electronics is a field gathering a growing interest among researchers and companies with widely varying applications, such as organic light emitting diodes, transistors as well as many different sensors. If the circuit should be portable or off-grid, the power sources available are batteries, supercapacitors or some type of power generator. Thermoelectric generators produce electrical energy by the diffusion of charge carriers in response to heat flux caused by a temperature gradient between junctions of dissimilar materials. As wearables, flexible electronics and intelligent packaging applications increase, there is a need for low-cost, recyclable and printable power sources. For such applications, printed thermoelectric generators (TEGs) are an interesting power source, which can also be combined with printable energy storage, such as supercapacitors. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), or PEDOT:PSS, is a conductive polymer that has gathered interest as a thermoelectric material. Plastic substrates are commonly used for printed electronics, but an interesting and emerging alternative is to use paper. In this article, a printed thermoelectric generator consisting of PEDOT:PSS and silver inks was printed on two common types of paper substrates, which could be used to power electronic circuits on paper.
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| 8. |
- Ballato, J., et al.
(författare)
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Material approaches to thermal management in advanced fiber lasers and amplifiers
- 2023
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510659797
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Konferensbidrag (refereegranskat)abstract
- For as long as light and matter have partnered, impurities have played a role in optical system performance. This remains generally true for photonic heat engines and especially the case for optical refrigeration. Building on the history of light and glass, including the materials development of low loss telecom fibers, this paper briefly discusses the sources of heat generation in materials and all-material means for their reduction. Particularly attention will be paid to active optical fibers and connect thermal management to parasitic optical nonlinearities, both critical to high and low power amplifier and laser systems.
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| 9. |
- Balliu, Enkeleda, PhD student, et al.
(författare)
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A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier
- 2019
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510624344 - 9781510624351 ; , s. 6pp-
-
Konferensbidrag (refereegranskat)abstract
- Interest in compact, single-frequency fiber amplifier has increased within many scientific and industrial applications. The main challenge is the onset of nonlinear effects, which limit their power scaling. Here we demonstrate a compact, high-power, single-frequency, polarization-maintaining, continous-wave fiber amplifier using only one amplification stage. We developed the fiber amplifier using a master oscillator fiber amplifier architecture, where a low-noise, single-frequency, solid-state laser operating at 1064 nm was used as a seed source. We evaluated the amplifier's performance by using several state-of-the-art, small-core, Ytterbium (yb)-doped fibers, as well as an in-house-made, highly Yb-doped fiber. An output power of 82 W was achieved with no sign of stimulated Brillouin scattering. A good beam quality and a polarization extinction ratio (PER) of > 25 dB were achieved. The compact fiber amplifier can be a competitive alternative to multi stage designed fiber amplifiers.
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| 10. |
- Balliu, Enkeleda, et al.
(författare)
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Compact nanosecond pulsed single stage Yb-doped fiber amplifier
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 9780819498724 ; , s. Art. no. 895910-
-
Konferensbidrag (refereegranskat)abstract
- In this work we present a compact, nanosecond pulsed, single frequency, single stage Yb-doped fiber amplifier by using an overall fiber core diameter of 20 μm. The key component is a custom made, compact, ultra-low noise, single frequency ring-cavity solid state laser (SSL) at 1064 nm used as a master oscillator. The SSL can be designed to provide nanosecond pulses with pulse energies in the sub-mJ range. Our ultimate goal is to develop a compact linearly polarized, single frequency, nanosecond pulsed laser source in an all-fiber format. Short (less than 1m), highly Yb-doped fibers have been used in order to suppress non-linear effects. © 2014 SPIE.
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| 11. |
- Balliu, Enkeleda, PhD student, et al.
(författare)
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Compact single-frequency mopa using a silica fiber highly doped with yb3
- 2021
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:21
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation.
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| 12. |
- Balliu, Enkeleda, et al.
(författare)
-
Laser-assisted reduction of graphene oxide for paper based large area flexible electronics
- 2016
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781628419719
-
Konferensbidrag (refereegranskat)abstract
- In this work we present a promising method for fabrication of conductive tracks on paper based substrates by laser assisted reduction of Graphene Oxide (GO). Printed electronics on paper based substrates is be coming more popular due to lower cost and recyclability. Fabrication of conductive tracks is of great importance where metal, carbon and polymer inks are commonly used. An emerging option is reduced graphene oxide (r-GO), which can be a good conductor. Here we have evaluated reduction of GO by using a 532 nm laser source, showing promising results with a decrease of sheet resistance from >100 M Ω/Sqr for unreduced GO down to 126 Ω/Sqr. without any observable damage to the paper substrates.
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| 13. |
- Balliu, Enkeleda, PhD student, et al.
(författare)
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Laser processing of graphene oxide on different coated paper substrates
- 2016
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Ingår i: 14th TAPPI Advanced Coating Symposium 2016. - : TAPPI Press. - 9781510877658 ; , s. 97-101
-
Konferensbidrag (refereegranskat)abstract
- Development of printed electronics is increasing each year, where many electrical components such as transistors and sensors are now printable. The most commonly used substrate have been plastics, but there is an increasing interest in using paper as substrate. The paper industry is a very large and mature industry with large production capacity and well developed processes. It is therefore of interest to investigate how it would be possible to combine printed electronics and paper based products. This can for example be to print sensors on packages, to use large scale roll-to-roll production for solar cells. To be able to achieve such goals it is of importance to develop methods of applying electrically active materials in the large, high speed roll-to-roll processes used in the paper industry. In this article we discuss coating of graphene oxide (GO) on large areas after which it is selectively reduced into electrically conductive reduced graphene oxide (rGO) by laser processing. Graphene oxide is an inexpensive, carbon based material very suitable to be deposited as a coating, and the selective activation of makes it possible to fabricate conductive patterns at high speeds. We have evaluated several different paper substrates on which GO was coated. The reduction was performed using an 532 nm laser source and the results are promising, showing that it is possible to fabricate selectively conductive patterns on paper substrates by coating and reduction of GO.
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| 14. |
- Balliu, Enkeleda, PhD student
(författare)
-
Power Scaling of Highly Compact Single-Frequency Yb-Doped Fiber Amplifiers
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Both scientific interests and industrial applications have stimulated the advance of single-frequency laser technology. The high spatial and temporal coherence of this technology has facilitated many applications such as gravitational wave detection, high-precision fiber sensors, high-resolution spectroscopy, holography, and nonlinear optical conversion. However, this is currently achieved through large footprint lasers with limited portability and mobility. Therefore, there is a need to reduce the size of these lasers into a compact format. Power performance of hundreds of watts in the near-infrared spectrum and tens of watts in the visible and UV spectra for continuous (CW) operation mode and pulse energies up to several tens of mJ in pulsed operation mode are needed. An amplification structure for single-frequency lasers that meets these requirements is the master oscillator power amplifier (MOPA). However, compactness imposes several constraints on the MOPA design. The main challenge is the limited output power of the single-frequency fiber MOPA due to the onset of stimulated Brillouin scattering (SBS) in the amplifier fiber. SBS arises from the interaction of acoustic phonons with the propagating signal wave and is converted into a frequency-shifted, backward-propagating wave. SBS is manifested through high-intensity pulses propagating in the backward direction, which can be very harmful for optical components and the seed laser itself. Hence, the suppression of SBS is crucial to the power optimization of the MOPA. This thesis therefore focuses on investigating different SBS suppression techniques that fit a compact MOPA design. More specifically, this is implemented by studying the efficiency of the strain distribution technique applied to the amplifier fiber and the use of custom and commercial highly Yb- doped fibers both in CW and pulse operating MOPAs. Using highly Yb-doped fibers presents challenges with respect to the composition of the fiber material and in high- power operation that can have undesirable degradational effects, such as photodarkening and thermal load generation, and these have been investigated and discussed in this thesis. As a result of the different mitigation approaches, output power approaching 100 W in CW mode operation and pulse energies near mJ in pulse mode operation are demonstrated in only one amplification stage, showing the feasibility of a MOPA design with high performance and a small footprint. This may facilitate many applications in the visible and UV spectral ranges that require mobility and portability.
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| 15. |
- Balliu, Enkeleda, PhD student, et al.
(författare)
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Quasi‐cw pumping of a single‐frequency fiber amplifier for efficient shg in ppln crystals with reduced thermal load
- 2022
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Single‐frequency lasers are essential for high‐resolution spectroscopy and sensing applications as they combine high‐frequency stability with low noise and high output power stability. For many of these applications, there is increasing interest in power‐scaling single‐frequency sources, both in the near‐infrared and visible spectral range. We report the second‐harmonic generation of 670 μJ at 532 nm of a single‐frequency fiber amplifier signal operating in the quasi‐continuous‐wave mode in a 10‐mm periodically poled Mg‐doped lithium niobate (MgO:PPLN) crystal, while increasing compactness. To the best of our knowledge, this is the highest pulse energy generated in this crystal, which may find applications in the visible and UV such as remote Raman spectroscopy.
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| 16. |
- Balliu, Enkeleda, et al.
(författare)
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Selective laser sintering of inkjet-printed silver nanoparticle inks on paper substrates to achieve highly conductive patterns
- 2018
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- Development of cost-effective and environmentally friendly manufacturing methods will enable important advances for the production of large-scale flexible electronics. Laser processing has shown to be a promising candidate that offers a fast and non-destructive way to produce highly conductive patterns on flexible substrates such as plastics. However, an emerging option with a lower environmental impact is instead the use of cellulose-based flexible substrates, such as paper. In this work we investigate the use of laser sintering of silver nanoparticle inks, which were inkjet-printed on three different types of paper. Patterns with a high conductivity could be manufactured where a special care was taken to prevent the substrates from damage by the intense laser light. We found that the best results was obtained for a photopaper, with a conductivity of 1.63 107 S/m corresponding to nearly 26% of the bulk silver conductivity. In addition, we demonstrate laser sintering to fabricate a fully functional near field communication tag printed on a photopaper. Our results can have an important bearing for the development of cost-effective and environmentally friendly production methods for flexible electronics on a large scale.
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| 17. |
- Balliu, Enkeleda, PhD student, et al.
(författare)
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Single-frequency, pulsed Yb3+-doped multicomponent phosphate power fiber amplifier
- 2020
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Ingår i: Journal of Optics. - : Institute of Physics Publishing (IOPP). - 2040-8978 .- 2040-8986. ; 22:11
-
Tidskriftsartikel (refereegranskat)abstract
- High-power, single-frequency, pulsed fiber amplifiers are required in light detection and ranging, coherent laser detection, and remote sensing applications to reach long range within a short acquisition time. However, the power-scaling of these amplifiers is limited by nonlinearities generated in the optical fibers, in particular by stimulated Brillouin scattering (SBS). In this regard, the use of multicomponent phosphate glasses maximizes the energy extraction and minimizes nonlinearities. Here, we present the development of a single-stage, hybrid, pulsed fiber amplifier using a custom-made multicomponent Yb-doped phosphate fiber. The performance of the phosphate fiber was compared to a commercial Yb-doped silica fiber. While the latter showed SBS limitation at nearly 6.5 kW for 40 cm length, the maximum achieved output peak power for the multicomponent Yb-doped phosphate fiber was 11.7 kW for 9 ns pulses using only 20 cm with no sign of SBS.
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| 18. |
- Bond, Luke, et al.
(författare)
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Laser-assisted processing of nano-graphite/silicon anode materials for improved performance of Li-ion batteries
- 2024
-
Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE - The International Society for Optics and Photonics. - 9781510670068
-
Konferensbidrag (refereegranskat)abstract
- Lithium-ion batteries are widely used today due to their high energy density, long life cycles, and low self-discharge rates. It commonly uses graphite as an anode material with a high theoretical capacity of 372mAh/g. At the same time, several research groups explore ways to further increase the energy storage capacity of lithium-ion batteries by, for example, adding silicon to the graphite anode material. Silicon is naturally abundant and inexpensive, with low environmental impact and a significantly higher theoretical specific capacity of ~4200mAh/g. A drawback is that graphite-silicon composite anode materials tend to degrade during the charge/discharge cycles, leading to decreased storage capacity over time. This degradation is associated with the size of the silicon particles, where large, micrometer-sized silicon particles are more susceptible to instability than smaller, nanometre-sized particles. To address this issue, we present an investigation using laser-assisted processing of nano-graphite-silicon composites. This process uses low-cost micrometer-sized silicon particles mixed with nano-graphite powder and a 1064 nm continuous wave laser to process the nano-graphite-silicon-coated anode material under various conditions and atmospheres (ambient and nitrogen). The performance of the lithium-ion battery is affected by different processing conditions. Specifically, the intensity of the 0.25V and 0.5V anodic peaks, which indicate the delithiation of silicon, is particularly affected, with the inclusion of an additional broader shoulder peak at around 0.3-0.35V. Our investigation suggests that laser-assisted processing of nano-graphite-silicon-composite materials is a scalable concept with the potential to improve the performance of nano-graphite-silicon anodes for lithium-ion batteries.
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| 19. |
- Bond, Luke, et al.
(författare)
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Production of Yb:YVO4 nanoparticles by pulsed laser ablation in liquid using a femtosecond laser
- 2024
-
Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE - The International Society for Optics and Photonics. - 9781510670044
-
Konferensbidrag (refereegranskat)abstract
- There is a growing demand for nanopowders and nanoparticles in fields like medicine, healthcare, optics, sensors, and environmental monitoring. To produce these particles, pulsed laser ablation in liquid is an emerging technology offering numerous benefits over more commonly used methods like chemical synthesis, despite its relatively low production rate. For photonics applications, the production of NPs via pulsed laser ablation in liquid of rare-earth doped crystals like YAG and YVO4 is of significant interest due to their high absorption and emission cross-section, as well as high thermal conductivity. There is an increasing interest in developing laser-active hybrid materials, such as nanoparticle-doped silica optical fibers, potentially offering new and unique optical properties in, e.g., fiber lasers. In this work, we present an investigation of using pulsed laser ablation in liquid to synthesize Yb:YVO4 nanoparticles using a 1030 nm femtosecond pulsed laser under various conditions. The size and structure of Yb:YVO4 nanoparticles were affected by the pulse repetition rate (frequency) and solvent parameters, producing ovoid-like and spherical structures in deionized water and ammonia solution, respectively, with increased colloidal stability utilizing ammonia. The produced NPs are in the 10 - 150 nm range, with smaller NPs formed using the ammonia solution. The NPs are characterized by dynamic light scattering, Raman spectroscopy, scanning electron microscopy and energy dispersive x-ray spectroscopy.
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| 20. |
- Edvardsson, Sverker, et al.
(författare)
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Accurate spin axes and solar system dynamics: climatic variations for the Earth and Mars
- 2002
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 384:2, s. 689-701
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Tidskriftsartikel (refereegranskat)abstract
- Celestial mechanical simulations from a purely classical point of view of the solar system, including our Moon and the Mars moons {Phobos and Deimos {are carried out for 2 millions of years before present. Within the classical approximation, the results are derived at a very high level of accuracy. Effects from general relativity for a number of variables are investigated and found to be small. For climatic studies of about 1 Myr, general relativity can safely be ignored. Three different and independent integration schemes are used in order to exclude numerical anomalies. The converged results from all methods are found to be in complete agreement. For verification, a number of properties such as spin axis precession, nutation, and orbit inclination for Earth and Mars have been calculated. Times and positions of equinoxes and solstices are continously monitored. As also observed earlier, the obliquity of the Earth is stabilized by the Moon. On the other hand, the obliquity of Mars shows dramatic variations. Climatic influences due to celestial variables for the Earth and Mars are studied. Instead of using mean insolation as in the usual applications of Milankovitch theory, the present approach focuses on the instantaneous solar radiation power (insolation) at each summer solstice. Solar radiation power is compared to the derivative of the icevolume and these quantities are found to be in excellent agreement. Orbital precessions for the inner planets are studied as well. In the case of Mercury, it is investigated in detail.
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| 21. |
- Engholm, Magnus, et al.
(författare)
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A bio-compatible fiber optic pH sensor based on a thin core interferometric technique
- 2019
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Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pH sensors concepts have been proposed, however, there is still a need for improved sensor solutions with respect to reliability, durability and miniaturization but also for multiparameter sensing. Here we present a conceptual verification, which includes theoretical simulations as well as experimental evaluation of a fiber optic pH-sensor based on a bio-compatible pH sensitive material not previously used in this context. The fiber optic sensor is based on a Mach-Zehnder interferometric technique, where the pH sensitive material is coated on a short, typically 20-25 mm thin core fiber spliced between two standard single mode fibers. The working principle of the sensor is simulated by using COMSOL Multiphysics. The simulations are used as a guideline for the construction of the sensors that have been experimentally evaluated in different liquids with pH ranging from 1.95 to 11.89. The results are promising, showing the potential for the development of bio-compatible fiber optic pH sensor with short response time, high sensitivity and broad measurement range. The developed sensor concept can find future use in many medical- or bio-chemical applications as well as in environmental monitoring of large areas. Challenges encountered during the sensor development due to variation in the design parameters are discussed. © 2019 by the authors.
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| 22. |
- Engholm, Magnus, et al.
(författare)
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A structural investigation of a synthesized precursor for fiber optical applications; the heterobimetallic ErNb_2(OPr^i)_13
- 2006
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 29:4, s. 386-391
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Tidskriftsartikel (refereegranskat)abstract
- A structural investigation of a synthesized precursor in a silica glass matrix is performed. Silica soot samples are doped with the heterobimetallic precursor ErNb2(OPri)13 by using a conventional solution doping technique and heat treatments to different temperatures. The precursor has also been introduced into a silica fiber preform by using the modified chemical vapor deposition technique. Analyses are made by using ultraviolet–visible–near infrared absorption spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and powder X-ray diffraction. It is concluded that an immiscible system of ErNbO4 crystallites and Nb2O5 is formed in the silica soot samples at high temperatures. Colloidal particles of ErNbO4 are also formed in the silica glass fiber preform showing interesting features.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Engholm, Magnus, et al.
(författare)
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Divalent Ytterbium in Ytterbium Doped Aluminosilicate Glass - Aspects on Photodarkening in Fiber Lasers
- 2007
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Ingår i: 2007 CONFERENCE ON LASERS & ELECTRO-OPTICS/QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2007), VOLS 1-5. - New York : IEEE conference proceedings. - 9781424435906 ; , s. 1902-1903
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Konferensbidrag (refereegranskat)abstract
- We show that divalent ytterbium ions are present in ytterbium doped aluminosilicate glass. The presence of Yb^2+-ions may influence the formation of induced color centers in ytterbium doped fiber lasers leading to reduced performance.
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| 27. |
- Engholm, Magnus, et al.
(författare)
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Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping
- 2009
-
Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 34:8, s. 1285-1287
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Tidskriftsartikel (refereegranskat)abstract
- We show that the photodarkening resistivity of ytterbium-doped fiber lasers can be greatly improved by cerium codoping. It is suggested that the coexistence of the redox couple Ce3+⁄Ce4+ in the glass provides means for trapping both hole- and electron-related color centers that are responsible for the induced optical losses in Yb-doped fiber lasers.
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| 28. |
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| 29. |
- Engholm, Magnus, et al.
(författare)
-
Materials optimization for ytterbium-doped high power fiber lasers
- 2008
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Ingår i: 2008 CONFERENCE ON LASERS AND ELECTRO-OPTICS & QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE, VOLS 1-9. - New York : IEEE conference proceedings. - 9781557528599 ; , s. 232-233
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Konferensbidrag (refereegranskat)abstract
- In this paper we will present paths to reduce the extent of photodarkening in ytterbium. doped fiber lasers based on the aluminosilicate glass matrix. This will enable higher powers and longer operating lifetimes.
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| 30. |
- Engholm, Magnus, et al.
(författare)
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On the origin of photodarkening resistance in Yb-doped silica fibers with high aluminum concentration
- 2021
-
Ingår i: Optical Materials Express. - 2159-3930 .- 2159-3930. ; 11:1, s. 115-126
-
Tidskriftsartikel (refereegranskat)abstract
- Ytterbium (Yb) doped silica fibers are widely used in high power fiber lasers where co-doping the silica core material with other elements is pivotal for high efficiency, lowdetrimental effects, and reliable optical properties. Aluminum (Al) is one of the most preferred co-dopants, yet, purely Yb/Al-doped silica fibers suffer from relatively high levels of photodarkening (PD) when used in laser applications. A slightly improved PD-resistance has been reported for increasing Al-doping concentration. However, the source of this improved performance is still unknown. In this article, we present the origin of the improved PD-resistance observed in Yb-doped silica fibers with high Al-concentration. It is found that a high Al-co-doping concentration reduces the interaction strength between the Yb-ion and nearby oxygen ions, resulting in a significant PD-resistance with negligible induced loss in the entire visible spectral range. A negligible PD is observed even for significantly higher Yb-concentrations than commonly used in commercially available Yb-doped silica fibers.
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| 31. |
- Engholm, Magnus, et al.
(författare)
-
Preventing Photodarkening in Ytterbium-Doped High Power Fiber Lasers; Correlation to the UV-Transparency of the Core Glass
- 2008
-
Ingår i: Optics Express. - 1094-4087. ; 16:2, s. 1260-1268
-
Tidskriftsartikel (refereegranskat)abstract
- Photodarkening experiments are performed on ytterbium-doped silicate glass samples. A strong charge-transfer (CT) absorption band near 230nm in aluminosilicate glass is found to be correlated to the mechanism of induced color center formation. Excitation into the CT-absorption band generates similar color centers as observed in ytterbium-doped fiber lasers under 915nm high power diode pumping. The position of the CT-absorption band is compositional dependent and is shifted to shorter wavelengths in ytterbium doped phosphosilicate glass. Very low levels of photodarkening is observed for the ytterbium doped phosphosilicate glass composition under 915nm high power diode pumping. Possible excitation routes to reach the CT-absorption band under 915nm pumping are discussed.
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| 32. |
- Engholm, Magnus, et al.
(författare)
-
Reduction of photodarkening in Yb/Al-doped fiber lasers
- 2008
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9780819470485 ; , s. U269-U276
-
Konferensbidrag (refereegranskat)abstract
- A strong charge-transfer band at UV-wavelengths is found to play a major role for the observed induced optical losses (photodarkening) in ytterbium doped high-power fiber lasers. This is correlated to the valence stability of the ytterbium ion in the silicate glass matrix, which we believe is the origin of photodarkening. We have performed UV-irradiation experiments on ytterbium-doped preform samples and accelerated photodarkening experiments on Yb-doped fibers, by using 915nm high power diodes. Our results show that photodarkening can be reduced, to low levels, either by preparing the preform glass in a reducing atmosphere or by hydrogen loading the fiber in a pressure chamber at room temperature.
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| 33. |
- Engholm, Magnus, et al.
(författare)
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Strong excited state absorption (ESA) in Yb-doped fiber lasers
- 2013
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Ingår i: FIBER LASERS X: TECHNOLOGY, SYSTEMS, AND APPLICATIONS. - : SPIE - International Society for Optical Engineering. - 9780819493705 ; , s. Art. no. 86010P-
-
Konferensbidrag (refereegranskat)abstract
- Excited state absorption (ESA) measurements performed on Yb-doped silica bers show the onset of a strong absorption band in the visible range. In this work, we perform experiments to investigate the possibility for ESA to be part of the induced optical losses (photodarkening) observed in Yb-doped ber lasers. Our results indicate that an ESA process, from the 2F5/2 excited state manifold in the Yb3+ ion to the charge-transfer state with absorption bands in the UV range, may constitute a transfer route for pump- and laser photons in the near-infrared range. © 2013 Copyright SPIE.
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| 34. |
- Engholm, Magnus, et al.
(författare)
-
Strong UV absorption and visible luminescence in ytterbium-doped aluminosilicate glass under UV excitation
- 2007
-
Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 32:22, s. 3352-3354
-
Tidskriftsartikel (refereegranskat)abstract
- A broad visible luminescence band and characteristic IR luminescence of Yb3+ ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made under both oxidizing and reducing conditions are analyzed. A strong charge-transfer absorption band in the UV range is observed for glass samples containing ytterbium. Additional absorption bands are observed for the sample made under reducing conditions, which are associated with f�d transitions of divalent ytterbium. The visible luminescence band is attributed to 5d�4f emission from Yb2+ ions, and the IR luminescence is concluded to originate from a relaxed charge-transfer transition. The findings are important to explain induced optical losses (photodarkening) in high-power fiber lasers.
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| 35. |
- Engholm, Magnus, et al.
(författare)
-
The role of charge transfer processes for the induced optical lossesin ytterbium doped fiber lasers
- 2009
-
Ingår i: The role of charge transfer processes for the induced optical lossesin ytterbium doped fiber lasers.
-
Konferensbidrag (refereegranskat)abstract
- In this paper we present how charge transfer processes influences the induced optical losses (photodarkening) in ytterbium doped fiber lasers. The location of the charge transfer absorption band is strongly composition dependent and is correlated to the valence stability of the ytterbium ion in the silicate glass matrix. An improved photodarkening performance can in general be observed for a charge-transfer band shifted to shorter wavelengths, although other routes are also possible to reduce photodarkening. Other parameters that affect the laser performance, such as absorption and emission cross section, must also be considered.
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| 36. |
- Frey, B. N., et al.
(författare)
-
Cooling Yb-Doped Silica Fibers and Fiber Lasers with Anti-Stokes Pumping
- 2023
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510659797
-
Konferensbidrag (refereegranskat)abstract
- Optical cooling in Yb-doped silica fibers using anti-Stokes fluorescence has become a subject of great interest in the fiber laser community. This paper provides an update on the development of silica fibers designed specifically to enhance their cooling properties. This growing list includes a new, nearly single-mode fiber with a borophosphosilicate core that produced –65 mK of cooling with only 260 mW of 1040-nm pump power. The silica compositions that have now been successfully cooled at atmospheric pressure by anti-Stokes fluorescence by our team include aluminosilicate, aluminofluorosilicate, borophosphosilicate, and aluminosilicate doped with one of three different alkali-earth nanoparticles (Ba, Sr, and Ca). By fitting the measured temperature dependence of the cooled fiber on pump power, two key parameters that control the degree of cooling are inferred, namely the critical quenching concentration and the absorptive loss due to impurities. The inferred values compiled for the fibers that cooled indicate that the extracted heat is highest when the Yb concentration is 2 wt.% or more (to maximize heat extraction), the Al concentration is ~0.8 wt.% or greater (to reduce quenching), and the absorptive loss is below approximately 15 dB/km, and ideally below 5 dB/km (to minimize heating due to pump absorption). Only two of the reported fibers, an LaF3-doped and an LuF3-doped nanoparticle fiber, did not cool, because their Yb and Al concentrations were not sufficiently high. This analysis shows that through careful composition control (especially the Al and Yb concentrations) and minimization of the OH contamination, a new generation of Yb-doped silica fibers is emerging with higher Yb concentrations, greater resistance to quenching, and lower residual loss than commercial Yb-doped fibers. They can be expected to have a significant impact not only on optically cooled devices but also on a much broader range of fiber lasers and amplifiers.
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| 37. |
- Hammarling, Krister, 1968-, et al.
(författare)
-
A combined glucose and pH sensor on a single optical fiber for continuous point-of-care testing
- 2018
-
Ingår i: SPIE BIOS, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII. - : SPIE - International Society for Optical Engineering.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Stress-induced hyperglycemia is very common for patients in intensive care units, which can become fatal if left uncontrolled. Blood glucose concentrations for patients at the intensive care units should therefore be monitored at all times. To be successful in monitoring the glucose concentrations of patients, the sensor needs to be fast, accurate and able to measure in real time. In addition, the pH level should be monitored, as a diagnostic parameter by itself, or to improve the reliability of the glucose measurement. To address this challenge, a fiber optic sensor for dual parameter measurement of glucose concentration and pH level for use in point-of-care testing has been developed. The sensor utilizes two stimuli responsive hydrogels to create two interferometers combined on one single mode fiber. The sensor is created by splicing a short section of thin-core fiber (SM450) coated with a pH-sensitive polymer, which constitutes a Mach-Zehnder type interferometer. The glucose is measured with a low finesse Fabry-Perot cavity made by polymerizing a glucose sensitive hydrogel hemisphere at the end face of the fiber. A versatile Fourier transform based, low pass filter was developed, which enable evaluation of the two signals independently. Our results show the feasibility of measuring glucose concentration and pH level by using a single fiber. This dual parameter and single point fiber optic biosensor is expected to be of great interest for in vivo measurements in medical applications where pH and glucose, as specific markers are monitored in real time, during or after surgery.
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| 38. |
- Hammarling, Krister, 1968-, et al.
(författare)
-
Broad-range hydrogel-based pH sensor with capacitive readout manufactured on a flexible substrate
- 2018
-
Ingår i: Chemosensors. - Basel, Switzerland : MDPI AG. - 2227-9040. ; 6:3
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental monitoring of land, water and air, is an area receiving greater attention because of human health and safety concerns. Monitoring the type of pollution and concentration levels is vital, so that appropriate contingency plans can be determined. To effectively monitor the environment, there is a need for new sensors and sensor systems that suits these type of measurements. However, the diversity of sensors suitable for low, battery powered- and large area sensor systems are limited. We have manufactured and characterized a flexible pH sensor using laser processing and blade coating techniques that is able to measure pH between 2.94 and 11.80. The sensor consists of an interdigital capacitance with a pH sensitive hydrogel coating. Thin sensors can reach 95% of their final value value within 3 min, and are stable after 4 min. Good repeatability was achieved in regard to cycling of the sensor with different pH and multiple measurements from dry state. We have also studied the relation between an interdigital capacitance penetration depth and hydrogels expansion. We believe that our passive sensor is suitable to be used in low power and large area sensor networks.
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| 39. |
- Hammarling, Krister, 1968-, et al.
(författare)
-
Dual parameter fiber optic sensor combining a Fabry-Perot and a Mach-Zehnder interferometer
- 2017
-
Ingår i: Proceedings of IEEE Sensors. - : IEEE. - 9781509010127 ; , s. 1440-1442
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A new concept for dual parameter fiber optic sensorhas been developed and characterized, both in a two-fiber andsingle-fiber configuration. The liquid sensor measures ethanolconcentration with a stimuli responsive hydrogel whichconstitutes a low finesse Fabry-Perot cavity, and refractive indexwith a Mach-Zehnder type fiber optic interferometer. The two-fiber configuration utilize a fiber optic 1310/1550 nm wavelengthdivision multiplexer to separate the two parameters, while aversatile filtering algorithm extracts and separates the twoparameters in the single-fiber configuration. No cross talk wereobserved for the measured parameters of free spectral range andrefractive index for the two-fiber configurations, while for thesingle fiber configuration cross-talk were observed. The twoconfigurations prove to be versatile dual parametric fiber opticsensor concepts for accurate detection of specific parameters,based on stimuli responsive hydrogels.
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| 40. |
- Hammarling, Krister, 1968-
(författare)
-
Hydrogel-based pH-sensors : Development and characterisation of optical and electrical pH sensors based on stimuli-responsive hydrogels
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ability to measure the chemical parameter pH is of high importance in many areas. With new government regulations and evolving markets, there is a strong motivation for improving such measurements and conducting research on new types of pH sensors and sensor materials. Stimuli-responsive hydrogels (a group of polymers) have attracted a lot of attention in recent decades, due to their ability to be customized to suit many applications. One specific area where they have attracted attention is pH sensor technology.Two stimuli-responsive hydrogels are used in this thesis. One is a non-toxic hydrogel, 1,4-acryl-terminated oligo(beta-amino esters) (1,4-AOBAE). Although it was previously used in drug- and DNA- delivery systems, it has not (to my knowledge) been used in a sensor configuration, and thus it is interesting to study. The second hydrogel, 1,3-acryl-terminated oligo(beta-amino esters) (1,3-AOBAE), is an improved variant of the first one. This improved hydrogel was synthesized because the original hydrogel crystallizes at room temperature, which meant that it was not optimal for various coating techniques. This hydrogel was characterized and verified for pH responsivity in two sensor configurations: electrical and optical. Designing a hydrogel for a specific application can be a complex procedure due to the many synthesizing parameters. For example, increasing a hydrogel's mechanical strength by introducing a higher degree of cross linking, leads to a smaller mesh size, which in turn leads to a lower diffusion rate and less solution absorption. The two hydrogels examined in this thesis respond to pH changes by absorbing or desorbing water; this change in the hydrogel's water content also changes its effective refractive index and permittivity. These changes can be measured using optical or electrical sensor systems. Three types of sensor systems were used in this thesis to verify the hydrogel's pH response and to ensure that they are suitable for use in thin-film techniques on various substrates (e.g. glass and plastic). The experimental results prove that these hydrogels are suitable for use in both electrical and optical sensor configurations. For electrical systems, a pH range of approximately 3-12 was achieved, and for optical, the range was approximately 2-12. These ranges can likely be improved, as the sensor film delaminated from the substrate at low pHs due to adhesion problems and as measurements above 12 were not conducted.The findings of this thesis could, after more research, have strong implications for the development of improved pH-sensor configurations, especially for medical and healthcare applications and in environmental monitoring.
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| 41. |
- Hammarling, Krister, 1968-, et al.
(författare)
-
Synthesis, Curing Behavior and Swell Tests of pH-Responsive Coatings from Acryl-Terminated Oligo(beta-Amino Esters)
- 2018
-
Ingår i: CHEMOSENSORS. - : MDPI AG. - 2227-9040. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- The ability of acryl-terminated oligo(beta-amino esters) (AOBAE) to be coated on fibers and printed electronics without solvents and to be cross-linked to a pH-responsive coatings, makes AOBAE-based coatings a potential type of pH-sensor coating. However, there are currently no reports of AOBAEs used as a pH-responsive coating material in sensor applications. Here we present an investigation of the synthesis, curing behavior and swell tests of AOBAEs. AOBAEs were synthesized from reacting an excess of asymmetric diacrylates with piperazine without the use of any solvents. They were then cross-linked to an insoluble network by UV-curing. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the AOBAEs. NMR was used to clarify the irregular structure of the AOBAE. FTIR was used to monitor the effects of UV-curing dose and air exposure on monomer conversion during curing. An interferometric technique was used to monitor the swelling behavior of the coating in response to pH variations. Swell experiments showed that the AOBAE also responded to pH variations after polymerization. Therefore, AOBAE is an interesting class of material with potential use as a pH responsive coating in optical-and printed electronics pH-sensors applications.
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| 42. |
- Hawkins, T. W., et al.
(författare)
-
Kilowatt power scaling of an intrinsically low Brillouin and thermo-optic Yb-doped silica fiber
- 2021
-
Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 38:12, s. F38-F49
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of optical fibers is dependent on both the fiber design and the materials from which it is made. While much of the development over the past few decades has focused on fiber geometry and microstructuring, more recent analyses have shown clear benefits of addressing parasitic nonlinearities at the origins of their light–matter interactions. Reported here are results on intrinsically low Brillouin and thermo-optic core fibers, fabricated using modified chemical vapor deposition. Specifically, fibers in the Yb-doped Al2O3−P2O5−B2O3−SiO2 system are developed based on how each glass constituent affects the material parameters that enable both stimulated Brillouin scattering (SBS) and transverse mode instability (TMI). One fiber, developed to be very heavily doped, exhibited thermo-optic and Brillouin gain coefficients up to ∼3 dB and 6 dB below conventional laser fibers, respectively. A second fiber, designed to approximate a commercial double-clad laser fiber, which necessitated lower doping levels, was output power scaled to over 1 kW with an efficiency over 70% and no observed photodarkening under conventional testing. Design curves for the enabling material properties that drive TMI and SBS also are provided as functions of compositions as a tool for the community to further study and develop intrinsically low-nonlinearity fiber lasers.
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| 43. |
- Knall, Jennifer, et al.
(författare)
-
Experimental comparison of silica fibers for laser cooling
- 2020
-
Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 45:14, s. 4020-4023
-
Tidskriftsartikel (refereegranskat)abstract
- Laser cooling in silica has recently been demonstrated, but there is still a lack of understanding on how fiber composition, core size, and OH- contamination influence cooling performance. In this work, six Yb-doped silica fibers were studied to illuminate the influence of these parameters. The best fiber cooled by -70 mK with only 170 mW/m of absorbed pump power at 1040 nm, which corresponds to twice as much heat extracted per unit length compared to the first reported laser cooling in silica. This new fiber has an extremely low OW loss and a higher Al concentration (2.0 wt.% Al), permitting a high Yb concentration (2.52 wt.% Yb) without incurring significant quenching. Strong correlations were found between the absorptive loss responsible for heating and the loss measured at 1380 nm due to absorption by OH-.
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| 44. |
- Knall, Jennifer, et al.
(författare)
-
Laser cooling in a silica optical fiber at atmospheric pressure
- 2020
-
Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 45:5, s. 1092-1095
-
Tidskriftsartikel (refereegranskat)abstract
- For the first time, to the best of our knowledge, laser cooling is reported in a silica optical fiber. The fiber has a 21-μm diameter core doped with 2.06 wt.% YbM3+ and co-doped with Al2O3 and F- to increase the critical quenching concentration by a factor of 16 over the largest reported values for the Yb-doped silica. Using a custom slow-light fiber Bragg grating sensor, temperature changes up to -50 mK were measured with 0.33 W/m of absorbed pump power per unit length at 1040 nm. The measured dependencies of the temperature change on the pump power and the pump wavelength are in excellent agreement with predictions from an existing model, and they reflect the fiber's groundbreaking quality for the radiation-balanced fiber lasers.
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| 45. |
- Knall, J. M., et al.
(författare)
-
Experimental observation of cooling in Yb-doped silica fibers
- 2020
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510633599
-
Konferensbidrag (refereegranskat)abstract
- Anti-Stokes fluorescence cooling in a silica-based fiber is reported for the first time. The fiber had a core with a 20-μm diameter doped with 2.06 wt.% Yb and co-doped with 0.86 wt.% Al and 0.88 wt.% F. Core-pumping the fiber with 1040- nm light, temperature changes as large at -50 mK were measured at atmospheric pressure. Temperature measurements were performed at 12 pump wavelengths, and the measured dependence of the temperature change as a function of pump wavelength was in excellent agreement with a previously reported model. With this model, the absorptive loss in the fiber was inferred to be less than 15 dB/km, and the critical quenching concentration to be ∼15.6 wt.% Yb. This combination of low loss and high quenching concentration (a factor of 16 times higher than the highest reported values for Yb-doped silica) is what allowed the observation of cooling. The temperature measurements were performed at atmospheric pressure using a custom slow-light fiber Bragg grating sensor with an improved thermal contact between the test fiber and the FBG. The improved method involves isopropanol to establish a good thermal contact between the two fibers. This eliminated a source of heating and enabled more accurate measurements of the cooled-fiber temperature. This improved temperaturemeasurement set-up also led to a new cooling record in a multimode Yb-doped ZBLAN fiber at atmospheric pressure. When pumped at 1030 nm, the fiber cooled by -3.5 K, a factor of 5.4 times higher than the previous record.
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| 46. |
- Knall, Jennifer M., et al.
(författare)
-
Radiation-Balanced Silica Fiber Amplifier
- 2021
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 127:1
-
Tidskriftsartikel (refereegranskat)abstract
- We report what we believe to be the first radiation-balanced fiber amplifier-a device that provides optical gain while experiencing no temperature rise. The gain medium is a silica fiber with a 21-mu m-diameter core highly doped with Yb3+ (2.52 wt. %) and codoped with 2.00 wt. % Al to reduce concentration quenching. The amplifier is core pumped with 1040-nm light to create anti-Stokes fluorescence cooling and gain in the core at 1064 nm. Using a custom slow-light fiber Bragg grating sensor with mK resolution, temperature measurements are performed at multiple locations along the amplifier fiber. A 4.35-m fiber pumped with 2.62 W produced 17 dB of gain, while the average fiber temperature remained slightly below room temperature. This advancement is a fundamental step toward the creation of ultrastable lasers necessary to many applications, especially low-noise sensing and high-precision metrology.
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| 47. |
- Knall, J., et al.
(författare)
-
Radiation-balanced silica fiber laser
- 2021
-
Ingår i: Optica. - 2334-2536. ; 8:6, s. 830-833
-
Tidskriftsartikel (refereegranskat)abstract
- In optically pumped lasers, heat generated by the quantum defect causes detrimental fluctuations in the output mode, frequency, and power. Common heat-mitigation techniques use bulky mechanical coolers that introduce vibrations, leading to laser frequency and amplitude noise. Here, we present a radiation-balanced fiber laser, optically cooled by anti-Stokes fluorescence (ASF). The gain medium is a silica fiber with a 21-µm-diameter core doped with 2.06 wt. % Yb3+ and co-doped with Al2O3 and F- to reduce concentration quenching. The laser was core-pumped at 1040 nm to create both gain at 1065 nm and ASF cooling at atmospheric pressure. We demonstrate a maximum output power of 114 mW with a slope efficiency of 41% while maintaining near-zero average temperature change. This result could enable the development of fiber lasers with unprecedented coherence and stability.
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| 48. |
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| 49. |
- Malmström, Mikael, et al.
(författare)
-
Photodarkening resistant Yb/Ce/Al silica 980 nm fiberlaser
- 2010
-
Ingår i: Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference. - Washington, D.C. : IEEE. - 9781557528902 ; , s. 5500412-
-
Konferensbidrag (refereegranskat)abstract
- A linearly polarized fiber laser emitting at 979 nm with an output power of 2 W is presented. By using a photodarkening-resistant Yb/Ce/Al-codoped silica fiber, degradation-free operation is achieved over several hours.
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| 50. |
- Maslik, Jan, et al.
(författare)
-
PEDOT:PSS temperature sensor ink-jet printed on paper substrate
- 2018
-
Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 13
-
Forskningsöversikt (refereegranskat)abstract
- In this work we present an ink-jet printed temperature sensor consisting of PEDOT:PSSprinted on paper suitable for packaging, flexible electronics and other printed applications. Thesubstrate showed to have a large influence on both the resistance aswell as the temperature sensitivityof the PEDOT:PSS ink. This effect is most likely due to NaCl content in the photo paper coating,which reacts with the PEDOT:PSS. The temperature coefficient of a prepared device of α= -0.030 relative to room temperature (22°C) was measured, which is higher than compared to for exampleSilicon α = -0.075.
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