Xuesheng Chen

Advances in nonradiative processes in solids

Nonradiative Relaxation of Solids: Different Pathways to the Ground State.- The Role of Nonradiative Processes in the Spectroscopy of Optically Active Centers in Solids.- Radiative and Nonradiative Rates in Luminescence Centers.- Advances in Non-Radiative Processes in Solid State Laser Materials.- Model Calculations of Nonradiative Multiphonon Processes in INORGANIC Insulating Solids.- Advances in Nonradiative Processes in Semiconductors.- Radiative and Nonradiative Processes in Color Centers.- Nonradiative Transitions Between Electronic Levels of Opticallyactive Ions in Glass.- Nonradiative Processes in Luminescent Materials: A Materials Scientists View.- Techniques for the Investigation of Nonradiative Processes.- New Applications of Efficient Phosphors.- Long Seminars.- Energy Transfer in Cr, Tm: Yag.- Luminescence and Nonradiative Processes in Porous Glasses.- Laser Spectroscopy Techniques Applied to Cr3+ -Doped Materials.- How to Play with Springs and Pulses in a Classical Harmonic Crystal.- Thermal Response and Decoupling of Excitations at Low Temperatures.- New Laser Crystals (Abstract only).- Degenerate Four-Wave Mixing Technique for Studying Very Fast Radiationless Processes in Very Short Time Scale.- Photothermal Optical Nonlinearities, Optical Bistability and Possible Applications.- Crystals: Growth Methods and Characterization.- 4He and 3He Calorimetric Absorption Spectroscopy: Principles and Results on Ingaas/Alinas Quantum Wells and Fe in InP and GaAs.- Special Topics (Abstracts).- Particles and Elementary Excitations.- Short Seminars (Abstracts).- Excited State Absorption in Tb Activated Phosphor Powders.- Picture of the Participants.- Participants.

Optical amplification in Nd3+ doped electro-optic lanthanum lead zirconate titanate ceramics

As high as 13.0dB single-pass gain was obtained at 1064.4nm in a thin electro-optic ceramic plate of neodymium doped lanthanum-modified lead zirconate titanate (Nd:PLZT). Pumping with a diode laser, gains were achieved in 1.0 and 0.5mol% Nd ion doped samples over a broad seed laser power ranging from tens of nanowatts to tens of milliwatts at room temperature. The broad absorption spectra of Nd:PLZT made it insensitive to the pump wavelength. The Nd:PLZT had a total scattering loss coefficient of less than 0.06cm−1 and exhibited a considerable quadratic electro-optic coefficient greater than 0.30×10−16m2∕V2.

Phonon effects on sharp luminescence lines of Nd3+ in Gd3Sc2Ga3O12 garnet (GSGG)

Abstract The widths, positions and shapes of sharp luminescence lines of the Nd3+ ion in GSGG:Cr3+, Nd3+ were measured carefully from 78 to 600 K. The sharp lines studied correspond to the R2 → Y1, R2 → Y1, R2 → Y3, R1 → Y2, R2 → Y6, R1 → Y6 and R1 → Z5 transitions. All the lines shift to the red with increasing temperature except for the R1 → Z5 line which shifts to the blue. The temperature dependence of line widths and line shifts is explained in terms of an ion-phonon interaction as a perturbation and of a Debye phonon distribution. The Debye temperature is treated as an adjustable parameter to get the best fit to the experiment data. The line widths are related to Raman scattering of phonons, direct phonon processes and statistical local strain of the crystal. The line shifts are due to the stationary effect of the ion-phonon interaction. The Debye temperature of GSGG is estimated to be 500 K through the fittings of the theoretical formulas to the experimental data.

Random lasing and weak localization of light in transparent Nd+3 doped phosphate glass

Random lasing action and weak localization of light were observed in multiple visible wavelengths with highly transparent, Nd+3 doped phosphate glass gain media, with strong energy redistribution between different frequencies under different pumping powers. A tentative model based on photoinduced scattering was proposed and verified with a He-Ne laser beam in probing the lasing zone. The remarkable coherency and intensity changes of the probing laser beam confirmed the local, random scattering behind the photoinduced random lasing and the localization of light.

Lasing action and optical amplification in Nd 3+ doped electrooptic lanthanum lead zirconate titanate ceramics

Both single-pass gain and lasing action at 1064.4 nm were observed in ceramic gain media of neodymium doped lanthanum-modified lead zirconate titanate, which exhibits good electrooptic (EO) effect from visible through mid-wave IR band (400 nm to 5.5 µm). These works have removed roadblocks off the way leading to development of long envisioned multifunctional optical devices. The impact of the Nd3+ doping concentration on the EO effect in the Nd3+:PLZT ceramics was studied. The finding of the slowly trailing-off was satisfactorily explained with the rich vacancy-based carrier traps, which are responsible for the long persistent optoenergy storage.

Temperature dependence of spectral linewidths and lineshifts of Nd3+ ions in CaY2Mg2Ge3O12 laser crystal

We have investigated the widths and shifts of the luminescence 4F3/2→4I9/2 line at 940 nm (R1→Z5) and of the 4F3/2→4I11/2 line at 1046 nm (R2→Y1) in the laser crystal CaY2Mg2Ge3O12:Nd3+,Cr3+ from 78 to 300 K. The linewidths are over 20 cm−1. The R2→Y1 line position was found to shift to a longer wavelength and the R1→Z5 to a shorter wavelength with increasing temperature. The results on the thermal line broadening and shifts are compared with the existing theory which uses a simplified ion‐phonon interaction as a perturbation and assumes a Debye phonon distribution for the solid.

Green and red luminescence of YSGG : Er under up-conversion and regular excitation at different Er concentrations

Green and red luminescence in Er-doped YSGG, excited in the infrared or blue, is investigated at two different Er concentrations, 1% and 30%. It is found that the green and red up-conversion luminescence under the infrared excitation in 30%Er : YSGG is much stronger than that in 1%Er : YSGG. Under the blue excitation, however, the green luminescence in 30%Er : YSGG is much weaker than that in 1%Er : YSGG. It is also found that the red luminescence in the low Er concentration (1%) doped YSGG is always very weak with either pumping scheme. The infrared to green and red up-conversion luminescence in Er : YSGG is shown to be mainly due to energy transfer up-conversion.

Optoenergy storage, stimulated processes in optical amplification with electro-optic ceramic gain media of Nd3+ doped lanthanum lead zirconate titanate

Optical amplification was observed in electro-optic (EO) ceramic plates of neodymium doped lanthanum-modified lead zirconate titanate (Nd3+:PLZT), when the pumping and seeding beams are not overlapped temporarily. This striking feature in the gain measurement and the accompanying slowly trailing-off both seen in the optical amplification as well as in the lasing action are satisfactorily explained by electron releasing from the rich vacancy-based carrier traps in the intrinsically disordered ceramics, i.e., the consecutively optical, thermal stimuli are found responsible for the long persistent optoenergy storage, and consequently the slow response of the gain dynamics. These findings in optical amplification, the slowly trailing-off, and the underlying mechanism have opened a new way of developing novel controllable optical devices. The model thus established could serve as a guide in design and refinement of a new generation of products out of this excellent, well commercialized EO PLZT ceramics family ...

Optical amplification in disordered electrooptic Tm3+ and Ho3+ codoped lanthanum-modified lead zirconate titanate ceramics and study of spectroscopy and communication between cations

Rare earth doped electro-optic (EO) ceramics of lanthanum-modified lead zirconate titanate (PLZT) are promising in building multifunctional optical devices, by taking advantage of both EO effect and optical activity. In this work, the combination of the measured spectra of absorption and photoluminescence, the fluorescent decay, the calculated Judd-Ofelt parameters, and measured single pass gain in Tm3+, Ho3+ codoped PLZT ceramics have marked them out as promising gain media in building electrically controllable lasers/optical amplifiers and other multifunctional devices. Optical energy storage was also observed in the optical amplification dynamics.

Up-conversion luminescence of Er3+-doped yttrium, scandium, gallium garnet at different temperatures

Abstract The up-conversion luminescence in the visible region (400–700 nm) from (30% Er 3+ -doped YSGG laser crystal was investigated in the temperature range of 77–300 K, when the crystal was pumped by a diode laser at ~ 790 nm. The spectra were compared with those under an Ar ion laser (~ 488 nm) pumping. The difference between the two sets of spectra and possible up-conversion processes were discussed.