Xu Xinguang

Eye-Safe Raman Laser at 1.5μm Based on BaWO4 Crystal

Using an external couple cavity and a pump beam compression system, efficient 1.5 μm eye-safe Raman laser is obtained based on BaWO4 crystal. The largest output energy is 8.5mJ, corresponding to an electric-optical conversion efficiency of 47%.

Raman Spectra of Deuterated Potassium Dihydrogen Phosphate Crystals with Different Degrees of Deuteration

The polarized Raman spectra of deuterated potassium dihydrogen phosphate crystals with different deuterium concentrations are measured. With the increasing deuterium concentration, the Raman peaks which are assigned as the internal vibrations of the (H/D)2PO−4 anion shift to lower wavenumbers. This red-shift contributes to the decrease in the bonding force of the P—O bond as a result of the substitution of deuterium for hydrogen. Moreover, the intensity of the strongest peak of these crystals decreases first, and reaches the minimum value while the mole percentage of the deuterium content in the crystal is about 74%. After that, the intensity increases with the increase of the deuterium concentration in the crystal.

Picosecond Stimulated Raman Scattering of SrWO4 Crystal

Stimulated Raman scattering (SRS) of picosecond pulses is investigated in a new crystal SrWO4. The second harmonic generation of a mode-locked Nd:YAG laser system is used as the pump source. In an external single-pass configuration, the SRS thresholds for the first to the fourth Stokes lines are measured. For the first Stokes line, the steady-state gain coefficient of the SrWO4 crystal is calculated to be 15.96 cm/GW. In our experiment, as many as five Stokes lines (559.23 nm, 589.61 nm, 623.49 nm, 661.50 nm, 704.44 nm) and three anti-Stokes lines (506.97 nm, 484.34 nm, 463.65 nm) are observed, and the total conversion efficiency is as high as 62%.

Two-photon absorption-induced emission properties of dye HMASPS doped polymer

The 0.01M two-photon absorption dye trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methyl-pyridinium p-toluene sulfonate (HMASPS) doped polymer has been prepared. When pumped by the picosecond pulse from the pulsed mode-locked Nd:YAG laser, the polymer emits more intense upconverted fluorescence and superradiance compared to the solution sample of the dye. The two-photon pumped lasing with oscillating pulses has also been obtained. Compared to the dye in its solution state, the emission spectra of the polymer are all blueshifted. The polymer has a long upconverted fluorescent lifetime of about 4.041?0.04?ns.

Effect of Pressure on Thermal Stability and Decomposition of KDP Crystal

Effect of pressure on thermal behavior of KDP crystals is investigated by using the in-situ infrared reflective spectra. Compared with that under normal atmosphere, the onset temperature of decomposition under pressure of 1 MPa is improved to from 210°C to 213°C, suggesting that the thermal stability of KDP is enhanced. Under pressure of 2 MPa, the thermal stability is deteriorated and KDP begins to decompose at 183°C. Under normal atmosphere KDP decomposes in route of translating to K4P2O7 firstly, and then to KPO3. Under pressures of 1 MPa and 2MPa, KDP translates to KPO3 directly without any other polymeric intermediates.

Effect of S Substitution for P Point Defects in KDP Crystals: First-Principles Study

The electronic structure and geometric distribution of phosphor replaced by sulfur in potassium dihydrogen phosphate (KDP) are investigated by first-principles calculations. The point defect narrows down the energy gap to about 4.9 eV, corresponding to a two-photon absorption of 355 nm after correction. This can explain the decrease of the laser damage resistance in KDP crystals. Moreover, the defects twist the crystal structure and weaken bonds, especially the O-H bonds, so these bonds may be the first sites to crack under laser irradiation.

Electrical Conduction in Deuterated Ammonium Dihydrogen Phosphate Crystals with Different Degrees of Deuteration

Conductivity measurements of deuterated ammonium dihydrogen phosphate (DADP) crystals with different deuterated degrees are described. The conductivities increase with the deuterium content, and the value of the a-direction is larger than that of the c-direction. Compared with DKDP crystals, DADP crystals have larger conductivities, which is partly due to the existence of A defects. The ac conductivity over the temperature range 25–170°C has shown a knee in the curve of ln(σT) versus T−1. The conductivity activation energy calculated by the slope of the high temperature region decreases with the deuterium content. The previously reported phase transition is not seen.

Raman gains of ADP and KDP crystals

In this paper, the Raman gain coefficients of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP) crystals are measured. By using a pump source of a 30-ps, 532-nm laser, the gain coefficients of ADP and KDP are 1.22 cm/GW, and 0.91 cm/GW, respectively. While for a 20-ps, 355-nm pump laser, the gain coefficients of these two crystals are similar, which are 1.95 cm/GW for ADP and 1.86 for KDP. The present results indicate that for ultra-violet frequency conversion, the problem of stimulated Raman scattering for ADP crystal will not be more serious than that for KDP crystal. Considering other advantages such the larger nonlinear optical coefficient, higher laser damage threshold, and lower noncritical phase-matching temperature, it can be anticipated that ADP will be a powerful competitor to KDP in large aperture, high energy third-harmonic generation or fourth-harmonic generation applications.

Raman Gain Coefficients of Nd:LuxY1−x VO4 Crystals

By using a pulse laser at 532.36nm as the incident light, stimulated Raman scattering (SRS) of a series of a-cut and c-cut Nd:LuxY1−xVO4 (x = 0, 0.10, 0.26, 0.41, 0.61, 0.67, 0.80) crystals is investigated. For the π-polarization (E||c), the gain coefficient reduced as x value increased. For the σ-polarization (E||a), the Raman gain of all of the mixed crystals is larger than the pure Nd:YVO4, and the maximum value is obtained from the Nd:Lu0.1Y0.9VO4 crystal. Such results are also supported by the measurement of spontaneous Raman scattering spectra.

Noise Reduction in Photorefractive Image Amplification by Contradirectional Two-Wave Mixing in Rh-Doped BaTiO3 Crystal

Low noise image amplification owing to contradirectional two-wave mixing (CTWM) is proposed and demonstrated in Rh-doped BaTiO3 crystal. Comparing with the conventional forward two-wave mixing scheme, an enhancement of signal-to-noise ratio in the order of 103 is obtained. The theoretical analyses are presented and give a reasonable explanation for the experimental results. The further discussion shows that CTWM scheme can also reduce the influence of the crystal absorption and crystal size on the two-wave mixing process to rise the signal beam gain.