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We used pump-probe technique to investigate recombination dynamics of photogenerated carriers in photodiodes consisting of InAs/GaInSb W-structured superlattices. Recombination time constants of 1.6 ns and 10 ns were measured under high and low powers, respectively.
Phonon-assisted anti-Stokes fluorescence has been observed in GaN film grown on Si (111) substrate. The donor-acceptor pairs and bound excitons have played primary roles in the generation of anti-Stokes fluorescence.
We have observed blue and red Stark shifts of two excitonic transition peaks in multiple GaN/AlN asymmetric coupled quantum wells due to increases in electric fields originating from spatial separation of photogenerated electrons and holes.
Mechanisms for anti-Stokes photoluminescence observed at room temperature from n-type free-standing GaN grown by MOCVD have been attributed by us to the competition between two-photon absorption and phonon-assisted absorption.
In this work, we present our new findings following our studies of the THz generation from InGaN/GaN multiple quantum wells (MQW's), pumped by a frequency-doubled sub-picosecond Ti:sapphire amplifier at the output wavelength of 395 nm. For the pump power of 320 mW, an average output power of 32 nW was measured in the frequency range of 300 GHz - 4.28 THz. Based on the photo luminescence (PL) spectra...
Coherent THz pulses at 328.2 mum were generated by mixing two CO2 laser frequencies based on collinear phase-matched difference-frequency generation in GaSe crystals. The highest average output power was measured to be 260 muW.
We have observed resonance-enhanced Stokes and anti-Stokes Raman scattering of coherent picosecond pulses by one as well as two longitudinal-optical phonons in GaN film grown on Si (111) substrate.
By investigating dependence of THz output power on pump polarization, ratios of elements for second-order nonlinear susceptibility tensor have been measured for GaSe, which significantly deviate from those dictated by Kleinmanpsilas symmetry and structural symmetry.
Upconversion of laser beam at 10.26 mum to 1.187 mum was achieved in a GaSe crystal via difference-frequency generation with the highest conversion efficiency measured to be 19%. Saturation due to pump depletion was evidenced.
Coherent ns pulses for 2nd, 3rd, and 4th harmonics of CO2 laser frequency were efficiently generated from GaSe crystals, with corresponding output peak powers as high as 443 W, 23 W, and 2 W, respectively.
We have evidenced hot and cold longitudinal-optical (LO) phonons induced by electric field and resonant Raman scattering in GaN/AlN triangular quantum well, probed by first-order and second-order resonant Raman scattering of 3-ps light pulses.
Broadband THz pulses have been generated from InGaN/GaN multiple quantum wells pumped by a frequency-doubled sub-picosecond laser amplifier at 395 nm. Enhanced THz emissions are strongly correlated with reduced photoluminescence intensities.
Under relatively high pump intensities, photoluminescence intensities across the miniband were greatly reduced, which was attributed to the existence of periodic electric fields caused by spatially-separated photogenerated electrons and holes in short-period type-II InAs/GaSb superlattices.
We have observed second-harmonic generation from AlxGa1-xN multilayers in reflection geometry and measured the ratio between two elements of the second-order susceptibility tensor.
We summarize our progress made on developing widely tunable monochromatic terahertz sources. They have been implemented based on difference-frequency generation (DFG) in GaSe, ZnGeP, and GaP crystals. Using a GaSe crystal, the output wavelength was tuned continuously in the range of 66.5 to 5664 m (from 150 to 1.77 cm with the peak power reaching 389 W. Such a high peak power corresponds to a conversion...
We have demonstrated that two-photon absorption in a 2-cm-thick bulk GaP crystal can be the mechanism for limiting the efficient generation of the ultrafast broadband THz pulses using short infrared laser pulses.
We demonstrate that longitudinal-optical phonons in type-II InAs/GaSb quantum wells can be used to up-convert photoluminescence. Such a phenomenon could be used to achieve laser-induced cooling of lattices.
The development of widely-tunable monochromatic THz sources is described. These sources are based on difference-frequency generation (DFG) in GaSe, ZnGeP2, and GaP, respectively. Using a GaSe crystal the output wavelength was tuned in the range of from 58.2 mum to 3540 mum (from 172 cm-1 to 2.82 cm-1) with the peak power reaching 209 W. On the other hand, based on DFG in a ZnGeP2 crystal the output...
The authors present the result of efficiently producing the THz radiations by using collinear phase-matched difference-frequency generation (DFG) in a GaP crystal. The authors have extended the THz output wavelengths to as long as 2830 mum. In addition, the peak power has reached 15.6 W. Since GaP is a cubic crystal, there is no need to rotate this in order to tune the output wavelength in a wide...
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