| 1. |
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| 2. |
- Billsten, Helena, et al.
(författare)
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Dynamics of energy transfer from lycopene to bacteriochlorophyll in genetically-modified LH2 complexes of Rhodobacter sphaeroides
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:12, s. 4127-4136
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Tidskriftsartikel (refereegranskat)abstract
- LH2 complexes from Rb. sphaeroides were modified genetically so that lycopene, with I I saturated double bonds, replaced the native carotenoids which contain 10 saturated double bonds. Tuning the S, level of the carotenoid in LH2 in this way affected the dynamics of energy transfer within LH2, which were investigated using both steady-state and time-resolved techniques. The S I energy of lycopene in n-hexane was determined to be similar to12 500 +/- 150 cm(-1), by direct measurement of the S-1-S-2 transient absorption spectrum using a femtosecond IR-probing technique, thus placing an upper limit on the S, energy of lycopene in the LH2 complex. Fluorescence emission and excitation spectra demonstrated that energy can be transferred from lycopene to the bacteriochlorophyll molecules within this LH2 complex. The energy-transfer dynamics within the mutant complex were compared to wild-type LH2 from Rb. sphaeroides containing the carotenoid spheroidene and from Rs. molischian1l7n, in which lycopene is the native carotenoid. The results show that the overall efficiency for Crt --> B850 energy transfer is similar to80% in lyco-LH2 and similar to95% in WT-LH2 of Rb. sphaeroides. The difference in overall Crt --> BChl transfer efficiency of lyco-LH2 and WT-LH2 mainly relates to the low efficiency of the Crt S-1 --> BChl pathway for complexes containing lycopene, which was 20% in lyco-LH2. These results show that in an LH2 complex where the Crt Si energy is sufficiently high to provide efficient spectral overlap with both B800 and B850 Q(y) states, energy transfer via the Crt S, state occurs to both pigments. However, the introduction of lycopene into the Rb. sphaeroides LH2 complex lowers the S-1 level of the carotenoid sufficiently to prevent efficient transfer of energy to the B 800 Q, state, leaving only the Crt S-1 --> B 850 channel, strongly suggesting that Crt S-1 --> BChl energy transfer is controlled by the relative Crt S-1 and BChl Q(y) energies.
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| 3. |
- Polívka, Tomáš, et al.
(författare)
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Direct observation of the S1 level of the carotenoid spheroidene using near-infrared femtosecond spectroscopy
- 2001
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Ingår i: Ultrafast Phenomena XII. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642625121 - 9783642565465 ; 66, s. 668-670
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Bokkapitel (refereegranskat)abstract
- In this work, we have determined the energy of the S1 state of the carotenoid spheroidene. The energy of this state is 13,400 ± 90 cm-1 at both 293 K and 186 K, showing that there is no temperature-induced shift of the S1 level. A discrepancy of about 800 cm-1 between the S1 energy determined here and that obtained from previous fluorescence and resonance Raman measurements is explained in terms of the different conformational species co-existing in the S1 excited state.
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| 4. |
- Polívka, Tornáš, et al.
(författare)
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Near-infrared time-resolved study of the S-1 state dynamics of the carotenoid spheroidene
- 2001
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 105:5, s. 1072-1080
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Tidskriftsartikel (refereegranskat)abstract
- Using a novel experimental approach based on near-infrared femtosecond absorption spectroscopy, we have determined the energy of the S-1 state of the carotenoid spheroidene. The energy of this state is 13 400 +/- 90 cm(-1) at both 293 and 186 K, showing that there is no temperature-induced shift of the S-1 level. A discrepancy of about 800 cm(-1) between the S-1 energy determined here and that obtained from previous fluorescence and resonance Raman measurements is explained in terms of the different conformational species coexisting in the S-1 excited state. Measurements of kinetics in the near-infrared region revealed that at least three relaxation processes take place after excitation of spheroidene into its S-2 state. Ultrafast S-2 --> S-1 internal conversion occurs within the first 300 fs, followed by vibrational cooling in the SI state, which occurs on a time scale of similar to 700 fs. The S-1 lifetime is 8 ps at 293 K, in good agreement with previous measurements of the S-1 --> S-N transition. A somewhat longer S-1 lifetime of 9.5 ps is observed at 186 K.
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| 5. |
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| 6. |
- Vazquez-Cordova, Sergio A., et al.
(författare)
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Erbium-doped spiral amplifiers with 20 dB of net gain on silicon
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:21, s. 25993-26004
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Tidskriftsartikel (refereegranskat)abstract
- Spiral-waveguide amplifiers in erbium-doped aluminum oxide on a silicon wafer are fabricated and characterized. Spirals of several lengths and four different erbium concentrations are studied experimentally and theoretically. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 12.9 cm and 24.4 cm and concentrations of 1.92 x 10(20) cm(-3) and 0.95 x 10(20) cm(-3), respectively. The noise figures of these samples are reported. Gain saturation as a result of increasing signal power and the temperature dependence of gain are studied.
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| 7. |
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| 8. |
- Vazquez-Cordova, Sergio A., et al.
(författare)
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High gain in erbium-doped channel waveguides
- 2017
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Ingår i: 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. Integration of multiple functions on an optical micro-chip is going to revolutionize the exploitation of optics for various applications such as communication, optical sensing, and biomedicine. One of the enabling functions is amplification at 1.5 μm [1]. Rare-earth-doped amplifiers typically deliver a net gain per unit length of only a few dB/cm [2]. In spiral-shaped channel waveguides a total internal net gain of 20 dB was demonstrated [3].The rare-earth-doped potassium double tungstates KY(WO 4 ) 2 , KGd(WO 4 ) 2 , and KLu(WO 4 ) 2 are widely investigated laser materials [4]. They are especially suited for optical amplification due to the high transition cross-sections of rare-earth ions in these materials. Moreover, the large inter-ionic distance between neighboring rare-earth sites may allow for higher erbium concentrations without the detrimental effect of energy-transfer upconversion (ETU). Recently an internal net gain of ~1000 dB/cm was demonstrated in ytterbium-doped channel waveguides [2]. Here we report optical gain at 1.53 μm in KGd x Lu y Er 1-x-y (WO 4 ) 2 channel waveguides doped with five different Er 3+ concentrations. When pumping the Er 3+ ions at 980 nm, a record-high internal net gain of 13 dB/cm is experimentally demonstrated, despite the fact that the intrinsic propagation losses in these surface waveguides were as high as 4 dB/cm. Using buried channel waveguides, which typically exhibit intrinsic propagation losses of only 0.2 dB/cm, and optimizing the erbium concentration and waveguide length, for a reasonable 500 mW of launched pump power a high total gain of ~40 dB can be achieved.
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| 9. |
- Vazquez-Cordova, Sergio A., et al.
(författare)
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High optical gain in erbium-doped potassium double tungstate channel waveguide amplifiers
- 2018
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 26:5, s. 6260-6266
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Tidskriftsartikel (refereegranskat)abstract
- We report on the optical-gain properties of channel waveguides patterned into lattice-matched KGdxLuyEr1-x-y(WO4)(2) layers grown onto undoped KY(WO4)(2) substrates by liquid phase epitaxy. A systematic investigation of gain is performed for five different Er3+ concentrations in the range of 0.75 to 10at.% and different pump powers and signal wavelengths. In pump-probe-beam experiments, relative internal gain, i.e., signal enhancement minus absorption loss of light propagating in the channel waveguide, is experimentally demonstrated, with a maximum value of 12 +/- 5 dB/cm for signals at the peak-emission wavelength of 1534.7 nm.
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| 10. |
- Vazquez-Cordova, S. A., et al.
(författare)
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Optical gain around 1.5 μm in erbium-doped waveguide amplifiers
- 2015
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Ingår i: 2015 17th International Conference on Transparent Optical Networks (ICTON). - : IEEE Computer Society. - 9781467378802
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Konferensbidrag (refereegranskat)abstract
- The development in the field of erbium-doped integrated waveguide amplifiers for the generation of broadband and high-speed optical amplification around 1.5 - 1.6 μm is discussed and current and future potential applications are explored. In erbium-doped amorphous aluminium oxide on a silicon wafer, an internal net gain per unit length of 2.0 dB/cm at the wavelength of 1533 nm and internal net gain over a bandwidth of 80 nm has been demonstrated. Spiral-waveguide amplifiers of different lengths and erbium concentrations have been studied and an internal net gain of 20 dB in the small-signal-gain regime has been achieved. Currently, a highly promising crystalline host material, potassium double tungstate, which provides high emission cross sections to rare-earth ions and has generated an internal net gain per unit length of > 1000 dB/cm when exploiting the ytterbium transition at 1 μm, is doped with erbium ions and tested for amplification around 1.5 - 1.6 μm.
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| 11. |
- Vázquez-Córdova, S. A., et al.
(författare)
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Spectroscopy of erbium-doped potassium double tungstate waveguides
- 2017
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Ingår i: Integrated Optics. - : SPIE - International Society for Optical Engineering. - 9781510606531
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Konferensbidrag (refereegranskat)abstract
- We report the spectroscopy of crystalline waveguide amplifiers operating in the telecom C-band. Thin films of erbiumdoped gadolinium lutetium potassium double tungstate, KGdxLuyEr1-x-y (WO4)2, are grown by liquid-phase epitaxy onto undoped potassium yttrium double tungstate (KYW) substrates and micro-structured by Ar+-beam etching. Channel waveguides with erbium concentrations between 0.45-6.35 × 1020 cm-3 are characterized. The transition cross-sections of interest are estimated. The effect of energy-transfer up-conversion (ETU) is experimentally investigated. Microscopic and macroscopic ETU parameters are extracted from a simultaneous analysis of 20 decay curves of luminescence on the transition 4I13/2 → 4I15/2. The correlation between ETU and the doping concentration is studied. Pump excited-state absorption (ESA) on the transition 4I11/2 → 4F7/2 is investigated via a direct ESA measurement using a double-modulation pump-probe technique. The effect of ESA is studied for different pump wavelengths. The pump wavelength of 984.5 nm is found to be favorable for the complete range of erbium concentrations.
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| 12. |
- Vazquez-Cordova, S. A., et al.
(författare)
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Spiral amplifiers in a-Al2O3:Er on a silicon chip with 20 dB internal net gain
- 2015
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Ingår i: INTEGRATED OPTICS. - : SPIE. - 9781628414554
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Konferensbidrag (refereegranskat)abstract
- Spiral-waveguide amplifiers in erbium-doped amorphous aluminum oxide are fabricated by RF reactive co-sputtering of 1-mu m-thick layers onto a thermally-oxidized silicon wafer and chlorine-based reactive ion etching. The samples are overgrown by a SiO2 cladding. Spirals with several lengths ranging from 13 cm to 42 cm and four different erbium concentrations between 0.5-3.0x10(20) cm(-3) are experimentally characterized. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 13 cm and 24 cm and erbium concentrations of 2x10(20) cm(-3) and 1x10(20) cm(-3), respectively. The obtained gain improves previous results by van den Hoven et al. in this host material by a factor of 9. Gain saturation as a result of increasing signal power is investigated. Positive net gain is measured in the saturated-gain regime up to similar to 100 mu W of signal power, but extension to the mW regime seems feasible. The experimental results are compared to a rate-equation model that takes into account migration-accelerated energy-transfer upconversion (ETU) and a fast quenching process affecting a fraction of the erbium ions. Without these two detrimental processes, several tens of dB/cm of internal net gain per unit length would be achievable. Whereas ETU limits the gain per unit length to 8 dB/cm, the fast quenching process further reduces it to 2 dB/cm. The fast quenching process strongly deteriorates the amplifier performance of the Al2O3:Er3+ waveguide amplifiers. This effect is accentuated for concentrations higher than 2x10(20) cm(-3).
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| 13. |
- Yong, Y. -S, et al.
(författare)
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Direct confocal lifetime measurements on rare-earth-doped media exhibiting radiation trapping
- 2017
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Ingår i: Optical Materials Express. - : OSA - The Optical Society. - 2159-3930 .- 2159-3930. ; 7:2, s. 527-532
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Tidskriftsartikel (refereegranskat)abstract
- Radiation trapping occurs in rare-earth-doped active media with strong spectral overlap of luminescence and ground-state absorption. It is demonstrated experimentally that a confocal measurement mitigates the influence of radiation trapping on the measured luminescence lifetime, hence allowing for direct extraction of the lifetime from the measured decay curves. The radiation trapping effect is largely suppressed by probing a small sample volume and rejecting the photons reemitted from the unpumped region. This non-destructive measurement method is applied to ytterbium (Yb3+) activated potassium double tungstate crystalline layers with Yb3+ concentrations ranging from 1.2 at.% up to 76 at.% (~8 × 1019 - 5 × 1021 cm-3). The measured lifetime values are comparable to the results reported for Yb3+-doped potassium double tungstate powder diluted in liquid.
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| 14. |
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| 15. |
- Yong, Yean-Sheng, et al.
(författare)
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Temperature-dependent absorption and emission of potassium double tungstates with high ytterbium content
- 2016
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 24:23, s. 26825-26837
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Tidskriftsartikel (refereegranskat)abstract
- We study the spectroscopic properties of thin films of potassium ytterbium gadolinium double tungstates, KYb0.57Gd0.43(WO4)(2), and potassium ytterbium lutetium double tungstates, KYb0.76Lu0.24(WO4)(2), specifically at the central absorption line near 981 nm wavelength, which is important for amplifiers and lasers. The absorption cross-section of both thin films is found to be similar to those of bulk potassium rare-earth double tungstates, suggesting that the crystalline layers retain their spectroscopic properties albeit having >50 at.% Yb3+ concentration. The influence of sample temperature is investigated and found to substantially affect the measured absorption cross-section. Since amplifiers and lasers typically operate above room temperature due to pump-induced heating, the temperature dependence of the peak-absorption cross-section of the KYb0.57Gd0.43(WO4)(2) is evaluated for the sample being heated from 20 degrees C to 170 degrees C, resulting in a measured reduction of peak-absorption cross-section at the transitions near 933 nm and 981 nm by similar to 40% and similar to 52%, respectively. It is shown that two effects, the change of Stark-level population and linewidth broadening due to intra-manifold relaxation induced by temperature-dependent electronphonon interaction, contribute to the observed behavior. The effective emission cross-sections versus temperature have been calculated. Luminescence-decay measurements show no significant dependence of the luminescence lifetime on temperature.
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| 16. |
- Yong, Y. -S, et al.
(författare)
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Temperature-dependent absorption and gain of ytterbium-doped potassium double tungstates for chip-scale amplifiers and lasers
- 2017
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Ingår i: Integrated Optics. - : SPIE - International Society for Optical Engineering. - 9781510606531
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Konferensbidrag (refereegranskat)abstract
- Ytterbium-doped potassium rare-earth double tungstate thin films are excellent candidates for highly efficient waveguide lasers, as well as high-gain waveguide amplifiers, with a record-high optical gain per unit length of 935 dB/cm recently demonstrated. However, the spectroscopic properties of these highly ytterbium-doped thin films and, in particular, their temperature dependence are not well investigated. These characteristics are required for the understanding of the behavior of the fabricated optical devices and crucial for further device optimization. We experimentally determined the absorption cross-sections for a potassium ytterbium gadolinium double tungstate, KYb0.57Gd0.43(WO4)2, thin film grown lattice matched onto an undoped KY(WO4)2 substrate. At room temperature, the peak cross-section value at 981 nm and the overall absorption spectrum are very similar to those of Yb-doped bulk potassium double tungstate crystals, although Yb is now the dominating rare-earth content. The temperature-dependent study shows a significant decrease of the absorption cross-section values at 933 nm and 981 nm with increasing temperature. We verify theoretically that this is due to the temperature dependence of fractional populations in the individual Stark levels of the absorbing crystal-field multiplet, in combination with the linewidth broadening with increasing temperature. Further investigations suggest that the broadening of absorption linewidth at 981 nm originates in the intra-manifold relaxation between the two lowest Stark levels of the ground state. Finally, the implications of the spectroscopic findings on the operating characteristics of waveguide amplifiers are investigated. Amplifiers operating at 80 °C are expected to exhibit only 67% of the maximum theoretical gain at room temperature.
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