Time filter

Source Type

Yasuhara R.,Japan National Institute for Fusion Science | Furuse H.,Japan Institute for Laser Technology
Optics Letters

The thermal-birefringence-induced depolarization in terbium gallium garnet (TGG) ceramics has been investigated experimentally. The depolarization ratio of 6.1 × 10-4 has been observed at the maximum input power of 117Wcw, which corresponds to a normalized laser power of p = 0.14. As predicted by the previously proposed theory, the amount of depolarization ratio and its slope with respect to the laser power of the ceramic TGG was approximately the same as that previously reported for high-quality-cut (111) single crystal. © 2013 Optical Society of America. Source

Yasuhara R.,Japan National Institute for Fusion Science | Furuse H.,Japan Institute for Laser Technology | Iwamoto A.,Japan National Institute for Fusion Science | Kawanaka J.,Osaka University | Yanagitani T.,Konoshima Chemical Co.
Optics Express

The temperature dependence of the thermo-optic effect in cryogenically cooled Yb:YAG ceramics was evaluated by measuring the thermo-optic coefficient (the derivative of refractive index with respect to temperature, i.e., dn/dT), thermal expansion coefficient (α), and thermal conductivity (κ) between 70 and 300 K. These parameters significantly improved at low temperature. Observed values indicated that a laser gain medium cooled to 70 K can sustain a thermal load up to 20 times higher than that at 300 K, for comparable thermo-optic effects. To our best knowledge, this is the first quantitative evaluation of the improvement in thermo-optic characteristics of cryogenically cooled Yb:YAG ceramics. © 2012 Optical Society of America. Source

Yasuhara R.,Japan National Institute for Fusion Science | Nozawa H.,Konoshima Chemical Co. | Yanagitani T.,Konoshima Chemical Co. | Motokoshi S.,Japan Institute for Laser Technology | Kawanaka J.,Osaka University
Optics Express

The temperature dependence of the thermo-optic effects in single crystal and ceramic TGG were evaluated by using the Fizou interferometer method. The temperature dependence of the refractive index and thermal expansion are significantly improved at low temperature for both ceramics and single crystals. Our estimation using a figure of merit indicated that a TGG ceramics cooled to liquid nitrogen temperature can reduce thermal wave-front distortion by a factor of up to 4.7 with respect to that at 300 K, and can reduce thermal birefringence effects by up to a factor of 12 with respect to those at 300 K. © 2013 Optical Society of America. Source

Mendonca L.,French Institute of Health and Medical Research | Hache F.,French Institute of Health and Medical Research | Changenet-Barret P.,French National Center for Scientific Research | Plaza P.,Ecole Normale Superieure de Paris | And 3 more authors.
Journal of the American Chemical Society

Motions of the trans-p-coumaric acid carbonyl group following the photoexcitation of the R52Q mutant of photoactive yellow protein (PYP) are investigated, for the first time, by ultrafast time-resolved circular dichroism (TRCD) spectroscopy. TRCD is monitored in the near-ultraviolet, over a time scale of 10 ps. Immediately after excitation, TRCD is found to exhibit a large negative peak, which decays within a few picoseconds. A quantitative analysis of the signals shows that, upon excitation, the carbonyl group undergoes a fast (â‰o0.8 ps) and unidirectional flipping motion in the excited state with an angle of ca. 17-53. For the subset of proteins that do not enter the signaling photocycle, TRCD provides strong evidence that the carbonyl group moves back to its initial position, leading to the formation of a nonreactive ground-state intermediate of trans conformation. The initial ground state is then restored within ca. 3 ps. Comparative study of R52Q and wild-type PYP provides direct evidence that the absence of Arg52 has no effect on the conformational changes of the chromophore during those steps. © 2013 American Chemical Society. Source

Chosrowjan H.,Japan Institute for Laser Technology | Taniguchi S.,Japan Institute for Laser Technology | Tanaka F.,Japan Institute for Laser Technology | Tanaka F.,Chulalongkorn University
FEBS Journal

The basic principles and main characteristics of the ultrafast time-resolved fluorescence upconversion technique (conventional and space-resolved), including requirements for nonlinear crystals, mixing spectral bandwidth, acceptance angle, etc., are presented. Applications to flavoproteins [wild-type (WT) FMN-binding protein and its W32Y, W32A, E13R, E13K, E13Q and E13T mutants] and photoresponsive proteins [WT photoactive yellow protein and its R52Q mutant in solution and as single crystals] are demonstrated. For flavoproteins, investigations elucidating the effects of ionic charges on ultrafast electron transfer (ET) dynamics are summarized. It is shown that replacement of the ionic amino acid Glu13 and the resulting modification of the electrostatic charge distribution in the protein chromphore-binding pocket substantially alters the ultrafast fluorescence quenching dynamics and ET rate in FMN-binding protein. It is concluded that, together with donor-acceptor distances, electrostatic interactions between ionic photoproducts and other ionic groups in the proteins are important factors influencing the ET rates. In WT photoactive yellow protein and the R52Q mutant, ultrafast photoisomerization dynamics of the chromophore (deprotonated trans-p-coumaric acid) in liquid and crystal phases are investigated. It is shown that the primary dynamics in solution and single-crystal phases are quite similar; hence, the photocycle dynamics and structural differences observed at longer time scales arise mostly from the structural restraints imposed by the crystal lattice rigidity versus the flexibility in solution. © 2014 FEBS. Source

Discover hidden collaborations