| 1. |
- Andersson-Engels, Stefan, et al.
(författare)
-
Deep-tissue optical imaging and photoactivation activities at biophotonics@tyndall
- 2016
-
Ingår i: Frontiers in Optics, FiO 2016. - 2162-2701. - 9781943580194
-
Konferensbidrag (refereegranskat)abstract
- Activities for deep tissue imaging and photoactivation will be presented. Wihin Biophotonics@Tyndall projects based on upconverting nanoparticles and ultrasound optical tomography will be pursued. Data from collaborative research will be given.
|
|
| 2. |
- Bengtsson, Alexander, et al.
(författare)
-
Characterization and modeling of acousto-optic signal strengths in highly scattering media
- 2019
-
Ingår i: Biomedical Optics Express. - 2156-7085. ; 10:11, s. 5565-5584
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrasound optical tomography (UOT) is an imaging technique based on the acousto-optic effect that can perform optical imaging with ultrasound resolution inside turbid media, and is thus interesting for biomedical applications, e.g. for assessing tissue blood oxygenation. In this paper, we present near background free measurements of UOT signal strengths using slow light filter signal detection. We carefully analyze each part of our experimental setup and match measured signal strengths with calculations based on diffusion theory. This agreement between experiment and theory allows us to assert the deep tissue imaging potential of similar to 5 cm for UOT of real human tissues predicted by previous theoretical studies [Biomed. Opt. Express 8, 4523 (2017)] with greater confidence, and indicate that future theoretical analysis of optimized UOT systems can be expected to be reliable. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
|
|
| 3. |
- Bott, Lukas Thomas, et al.
(författare)
-
Coulomb dissociation of O-16 into He-4 and C-12
- 2023
-
Ingår i: NUCLEAR PHYSICS IN ASTROPHYSICS - X, NPA-X 2022. - : EDP Sciences. - 2100-014X. ; 279
-
Konferensbidrag (refereegranskat)abstract
- We measured the Coulomb dissociation of O-16 into He-4 and C-12 within the FAIR Phase-0 program at GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section O-16(alpha,gamma)C-12, which is the time reversed reaction to C-12(alpha,gamma)O-16. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the (RB)-B-3 setup were necessary to cope with the high-intensity O-16 beam. All tracking detectors were designed to let the unreacted O-16 ions pass, while detecting the C-12 and He-4.
|
|
| 4. |
- Gunther, Jacqueline, et al.
(författare)
-
Deep tissue imaging with acousto-optical tomography and spectral hole burning with slow light effect : A theoretical study
- 2018
-
Ingår i: Journal of Biomedical Optics. - 1083-3668. ; 23:7
-
Tidskriftsartikel (refereegranskat)abstract
- Biological tissue is a highly scattering medium that prevents deep imaging of light. For medical applications, optical imaging offers a molecular sensitivity that would be beneficial for diagnosing and monitoring of diseases. Acousto-optical tomography has the molecular sensitivity of optical imaging with the resolution of ultrasound and has the potential for deep tissue imaging. Here, we present a theoretical study of a system that combines acousto-optical tomography and slow light spectral filters created using spectral hole burning methods. Using Monte Carlo simulations, a model to obtain the contrast-to-noise ratio (CNR) deep in biological tissue was developed. The simulations show a CNR > 1 for imaging depths of ∼5 cm in a reflection mode setup, as well as, imaging through ∼12 cm in transmission mode setups. These results are promising and form the basis for future experimental studies.
|
|
| 5. |
- Gunther, Jacqueline, et al.
(författare)
-
Theoretical study of combined acousto-optical tomography and slow light filters
- 2018
-
Ingår i: Optical Tomography and Spectroscopy, OTS 2018. - 9781557528209 ; Part F90-OTS 2018
-
Konferensbidrag (refereegranskat)abstract
- Monte Carlo simulations were used to determine the contrast-to-noise ratio of acoustooptical tomographic imaging with slow light filters versus possible imaging depth. Both reflection and transmission setups were considered. The theoretical model showed that imaging through 12 cm of breast tissue could be plausible.
|
|
| 6. |
- Walther, Andreas, et al.
(författare)
-
Analysis of the potential for non-invasive imaging of oxygenation at heart depth, using ultrasound optical tomography (UOT) or photo-acoustic tomography (PAT)
- 2017
-
Ingår i: Biomedical Optics Express. - 2156-7085. ; 8:10, s. 4523-4536
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the important medical implications, it is currently an open task to find optical non-invasive techniques that can image deep organs in humans. Addressing this, photo-acoustic tomography (PAT) has received a great deal of attention in the past decade, owing to favorable properties like high contrast and high spatial resolution. However, even with optimal components PAT cannot penetrate beyond a few centimeters, which still presents an important limitation of the technique. Here, we calculate the absorption contrast levels for PAT and for ultrasound optical tomography (UOT) and compare them to their relevant noise sources as a function of imaging depth. The results indicate that a new development in optical filters, based on rare-earth-ion crystals, can push the UOT technique significantly ahead of PAT. Such filters allow the contrastto- noise ratio for UOT to be up to three orders of magnitude better than for PAT at depths of a few cm into the tissue. It also translates into a significant increase of the image depth of UOT compared to PAT, enabling deep organs to be imaged in humans in real time. Furthermore, such spectral holeburning filters are not sensitive to speckle decorrelation from the tissue and can operate at nearly any angle of incident light, allowing good light collection. We theoretically demonstrate the improved performance in the medically important case of non-invasive optical imaging of the oxygenation level of the frontal part of the human myocardial tissue. Our results indicate that further studies on UOT are of interest and that the technique may have large impact on future directions of biomedical optics.
|
|
| 7. |
- Afzelius, Mikael, et al.
(författare)
-
Demonstration of Atomic Frequency Comb Memory for Light with Spin-Wave Storage
- 2010
-
Ingår i: Physical Review Letters. - 1079-7114. ; 104:4
-
Tidskriftsartikel (refereegranskat)abstract
- We present a light-storage experiment in a praseodymium-doped crystal where the light is mapped onto an inhomogeneously broadened optical transition shaped into an atomic frequency comb. After absorption of the light, the optical excitation is converted into a spin-wave excitation by a control pulse. A second control pulse reads the memory (on-demand) by reconverting the spin-wave excitation to an optical one, where the comb structure causes a photon-echo-type rephasing of the dipole moments and directional retrieval of the light. This combination of photon-echo and spin-wave storage allows us to store submicrosecond (450 ns) pulses for up to 20 mu s. The scheme has a high potential for storing multiple temporal modes in the single-photon regime, which is an important resource for future long-distance quantum communication based on quantum repeaters.
|
|
| 8. |
|
|
| 9. |
- Alqedra, Mohammed K., et al.
(författare)
-
Optical coherence properties of Kramers' rare-earth ions at the nanoscale for quantum applications
- 2023
-
Ingår i: Physical Review B. - 2469-9950. ; 108:7
-
Tidskriftsartikel (refereegranskat)abstract
- Rare Earth (RE) ion doped nanomaterials are promising candidates for a range of quantum technology applications. Among RE ions, the so-called Kramers' ions possess spin transitions in the GHz range at low magnetic fields, which allows for high-bandwidth multimode quantum storage, fast qubit operations as well as interfacing with superconducting circuits. They also present relevant optical transitions in the infrared. In particular, Er3+ has an optical transition in the telecom band, while Nd3+ presents a high-emission-rate transition close to 890 nm. In this paper, we measure spectroscopic properties that are of relevance to using these materials in quantum technology applications. We find the inhomogeneous linewidth to be 10.7 GHz for Er3+ and 8.2 GHz for Nd3+, and the excited state lifetime T1 to be 13.68 ms for Er3+ and 540μs for Nd3+. We study the dependence of homogeneous linewidth on temperature for both samples, with the narrowest linewidth being 379 kHz (T2=839 ns) for Er3+ measured at 3 K, and 62 kHz (T2=5.14μs) for Nd3+ measured at 1.6 K. Further, we investigate time-dependent homogeneous linewidth broadening due to spectral diffusion and the dependence of the homogeneous linewidth on magnetic field to get additional clarity of mechanisms that can influence the coherence time. In light of our results, we discuss two applications: single qubit-state readout and a Fourier-limited single photon source.
|
|
| 10. |
- Amari, Atia, et al.
(författare)
-
Towards an efficient atomic frequency comb quantum memory
- 2010
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 130:9, s. 1579-1585
-
Konferensbidrag (refereegranskat)abstract
- We present an efficient photon-echo experiment based on atomic frequency combs [Phys. Rev. A 79 (2009) 052329]. Echoes containing an energy of up to 35% of that of the input pulse are observed in a Pr3+ -doped Y2SiO5 crystal. This material allows for the precise spectral holeburning needed to make a sharp and highly absorbing comb structure. We compare our results with a simple theoretical model with satisfactory agreement. Our results show that atomic frequency combs has the potential for high-efficiency storage of single photons as required in future long-distance communication based on quantum repeaters. (c) 2010 Elsevier B.V. All rights reserved.
|
|
| 11. |
- Barmann, P, et al.
(författare)
-
Spatially and temporally resolved electron density measurements in streamers in dielectric liquids
- 1997
-
Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 30:5, s. 856-863
-
Tidskriftsartikel (refereegranskat)abstract
- Spatially and temporally resolved spectroscopic measurements of light emitted from positive streamers in transformer oil are presented. Analyses of the measurements performed with a DC needle-plane gap yield electron densities and indications of the atomic excitation temperatures in the streamers. The hydrogen emission reveals an electron density below 10(16) cm(-3) during the main part of the streamer propagation time (80-90%). Later the light is also characterized by emission from a high-density plasma with electron densities in the range 10(18)-10(19) cm(-3). The electron density during this time increases approximately linearly with distance from the initiation point and a density factor of four higher has been measured at the streamer tip than at the root. Measurements with high spectral resolution detect both high and low electron densities simultaneously. A tentative model of the interior of the streamer plasma, spatially resolved, is presented.
|
|
| 12. |
- Barmann, P, et al.
(författare)
-
Spectroscopic measurements of streamer filaments in electric breakdown in a dielectric liquid
- 1996
-
Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 29:5, s. 1188-1196
-
Tidskriftsartikel (refereegranskat)abstract
- Emission spectroscopy has been utilized to provide information about the electron density and temperature in streamers and breakdown arcs in transformer oil. Recorded spectra include strongly broadened hydrogen Balmer-alpha lines and vibration/rotation band profiles of the C-2 molecule. The origin of the observed broadening of hydrogen lines is discussed and it is concluded that it arises mainly from collisions with charged particles, so-called dynamic Stark broadening. By assuming that the broadening is due solely to dynamic Stark broadening, electron densities between 1 x 10(18) and 1 x 10(19) cm(-3) were obtained for the rear of positive streamer filaments during the later stages of propagation. For negative streamers we obtained an upper limit of 3 x 10(16) cm(-3) and for breakdown arcs electron densities up to 4 x 10(18) cm(-3). The temperature information in the C-2 emission profiles and the intensity ratio of the hydrogen Balmer lines are discussed. Rough estimations of the temperature are presented both for positive and for negative streamers.
|
|
| 13. |
- Bartholomew, John G., et al.
(författare)
-
High-resolution spectroscopic techniques for studying rare-earth ions in nanoparticles
- 2023
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 257
-
Tidskriftsartikel (refereegranskat)abstract
- Rare-earth doped nanoparticles can exhibit narrow optical and spin linewidths at low temperatures. These outstanding properties for nanomaterials make them attractive for quantum technologies based on optically addressable spins such as quantum memories and computers. Although accurate linewidth measurements have been reported using, for example, spectral hole burning or photon echo techniques, so far they have been mostly restricted to large ensembles of particles. Being able to extend linewidths measurements to few and single particles is particularly important in view of their integration in nanophotonic devices. In this paper, we present techniques for determining inhomogeneous and homogeneous linewidths of small ensembles of rare-earth ions in doped nanoparticles with high signal-to-noise ratios for convenient integration times. Using these techniques we have observed property variations for particles from the same synthesis, a first step towards their optimization for applications in quantum technologies.
|
|
| 14. |
- Belfrage, Christina, et al.
(författare)
-
Doppler-Free Laser Spectroscopy Measurements on a Ne Discharge for Determination of 22Ne-20Ne Isotope Shifts
- 1983
-
Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 27:5, s. 357-370
-
Tidskriftsartikel (refereegranskat)abstract
- We have used Doppler-free polarization spectroscopy, intermodulated fluorescence and intermodulated optogalvanic spectroscopy for measuring isotope shifts in 6 Ne lines connecting the 2p53s and 2p53p configurations. The measurements were performed on two different hollow cathodes. For the 5852, 5882, 5945, 5976, 6143 and 6164 A lines the 22Ne-20Ne isotope shift was found to be 2300(15), 1740(2), 1717(3), 1728(5), 1669(4) and 1663(5) MHz, respectively. These results are in fair agreement with previous optical spectroscopy data.
|
|
| 15. |
|
|
| 16. |
- Bengtsson, Alexander, et al.
(författare)
-
Comparison of contrast-to-noise ratios of different detection methods in ultrasound optical tomography
- 2022
-
Ingår i: Biomedical Optics Express. - 2156-7085. ; 13:9, s. 4834-4850
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrasound optical tomography (UOT) is a hybrid imaging modality based on interaction between ultrasound and light, with a potential to extend optical imaging capabilities in biological tissues to depths of several centimeters. Several methods have been developed to detect the UOT signal. To better understand their potential for deep tissue imaging, we present a theoretical contrast-to-noise comparison between the spectral hole burning, single-shot off-axis holography, speckle contrast, and photorefractive detection methods for UOT. Our results indicate that spectral hole burning filters have the potential to reach the largest imaging depths. We find that digital off-axis holography and photorefractive detection can have good contrast-to-noise ratio at significant depths. The speckle contrast method has a smaller penetration depth comparatively.
|
|
| 17. |
|
|
| 18. |
- Bengtsson, Magnus, et al.
(författare)
-
Fluorescence lidar imaging of fungal growth on high-voltage outdoor composite insulators
- 2005
-
Ingår i: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 43:6, s. 624-632
-
Tidskriftsartikel (refereegranskat)abstract
- Remote fluorescence imaging of fungal growth on polymeric high-voltage insulators was performed using a mobile lidar system with a laser wavelength of 355 nm. Insulator areas contaminated by fungal growth could be distinguished from clean surfaces and readily be imaged. The experiments were supported by detailed spectral studies performed in laboratory using a fibre-optic fluorosensor incorporating an optical multi-channel analyser system (OMA) and a nitrogen laser emitting radiation at 33 7 nm.
|
|
| 19. |
- Bengtsson, Magnus, et al.
(författare)
-
Fungus covered insulator materials studied with laser-induced fluorescence and principal component analysis
- 2005
-
Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 59:8, s. 1037-1041
-
Tidskriftsartikel (refereegranskat)abstract
- A method combining laser-induced fluorescence and principal component analysis to detect and discriminate between algal and fungal growth on insulator materials has been studied. Eight fungal cultures and four insulator materials have been analyzed. Multivariate classifications were utilized to characterize the insulator material, and fungal growth could readily be distinguished from a clean surface. The results of the principal component analyses make it possible to distinguish between algae infected, fungi infected, and clean silicone rubber materials. The experiments were performed in the laboratory using a fiber-optic fluorosensor that consisted of a nitrogen laser and an optical multi-channel analyzer system.
|
|
| 20. |
- Bengtsson, Magnus, et al.
(författare)
-
Lidar fluorescence measurements of algal growth on electrical insulators
- 2003
-
Ingår i: 2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666). - 0780377346 ; , s. 473-473
-
Konferensbidrag (refereegranskat)abstract
- Fluorescence measurements using lidar techniques have been shown to be useful for monitoring of algal growth on e.g. historical monuments. In this experiment similar measurements were performed on electrical insulators to examine the correlation between algal growth and the quality of the insulator, a factor of importance in the high-voltage grid management
|
|
| 21. |
- Bengtsson, Magnus, et al.
(författare)
-
Remote laser-induced breakdown spectroscopy for the detection and removal of salt on metal and polymeric surfaces
- 2006
-
Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 60:10, s. 1188-1191
-
Tidskriftsartikel (refereegranskat)abstract
- The detection of contamination such as salt in outdoor high-voltage insulator systems and its subsequent removal are vital for a reliable transmission of electric power. Remote detection of salt on a copper metal surface was carried out by using a mobile laser-induced breakdown spectroscopy (LIBS) Lidar system with a laser wavelength of 355 nm. Detection of salt on a polymeric high-voltage insulator was obtained when an additional lens was inserted into the beam path, and the number of photons that was detected could be calculated by using a calibrated white light source. Ablative cleaning could readily be carried out with LIBS and was verified by observing the disappearance of the sodium D-line emission.
|
|
| 22. |
- Bengtsson, Per Erik, et al.
(författare)
-
Rotational cars thermometry in sooting flames
- 1992
-
Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 81:1-3, s. 129-140
-
Tidskriftsartikel (refereegranskat)abstract
- Coherent anti-Stokes Raman scattering of pure rotational transitions, rotational CARS, is demonstrated as an efficient method for temperature determination in sooting flames. The dual broadband CARS approach was used to measure temperature profiles in premixed, sooting ethylene flames at atmospheric pressure by probing the nitrogen gas. The recorded spectra were of equally high quality in non-sooting and sooting flames with volume fractions of soot of up to 7 x 10 7 cm3 soot/cm3The advantages of rotational CARS in comparison with several other techniques for the measurement of temperatures in sooting flames, and the general applicability of the technique to different combustion conditions, are discussed. Potential limitations in the application of rotational CARS to sooting flames that are more heavily sooting than the ones investigated in this study, are outlined.
|
|
| 23. |
- Bengtsson, Per-Erik, et al.
(författare)
-
Vibrational CARS thermometry in sooty flames: Quantitative evaluation of C2 absorption interference
- 1990
-
Ingår i: Combustion and Flame. - 0010-2180. ; 82:2
-
Tidskriftsartikel (refereegranskat)abstract
- The application of nitrogen vibrational CARS thermometry to sooty, premixed, atmospheric pressure flames has been investigated using a Nd:YAG laser based system. It was found that laser-produced C2 radicals strongly absorb part of the fundamental band peak in the CARS spectrum. This was the most severe interference to the CARS signal. A quantitative investigation of temperature errors caused by the C2 absorption effect is presented. The correlation between the absorption interference and the soot volume fraction was examined for different flame conditions. Also, the increase of the nonresonant susceptibility in sooty flame regions is clearly illustrated and its effect on thev evaluated temperature is quantitatively determined. The single-shot temperature standard deviation has also been investigated in flames with different soot loadings. Finally, other interference effects to the CARS signals in sooty flames are described and discussed.
|
|
| 24. |
- Bondza, Saskia, et al.
(författare)
-
A simple experimental method for measuring the thermal sensitivity of single-mode fibers
- 2020
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 91:10
-
Tidskriftsartikel (refereegranskat)abstract
- We present a simple technique to experimentally determine the optical-path length change with temperature for optical single-mode fibers. Standard single-mode fibers act as natural low-finesse cavities, with the Fresnel reflection of the straight cleaved surfaces being ∼3%, for the laser light coupled to them. By measuring the intensity variations due to interference of light reflected from the fiber front and end surfaces, while ramping the ambient temperature, the thermal sensitivity of the optical-path length of the fiber can be derived. Light was generated by a narrow linewidth, low drift laser. With our fairly short test fibers, we found that it was possible to reach a relative precision of the temperature sensitivity, compared to a reference fiber, on the 0.4%-2% scale and an absolute precision of 2%-5%, with the potential to improve both by an order of magnitude. The results for single-acrylate, dual-acrylate, and copper- and aluminum-coated fibers are presented. Values are compared with analytic models and results from a finite element method simulation. With the aid of these measurements, a simple fiber-interferometer, which is insensitive to thermal drifts, could be constructed.
|
|
| 25. |
|
|
