Zhenxiang Cheng

Growth and investigation of efficient self-frequency-doubling NdxGd1−xCa4O(BO3)3 crystal

Abstract In GdCa 4 O(BO 3 ) 3 (GdCOB) crystal, the Gd 3+ ions can be substituted by Nd 3+ ions within the concentration of 0–100xa0at%. Combined laser action of the Nd 3+ ions and nonlinear optical (NLO) properties of GdCOB crystal host in the mixed Nd x Gd 1− x COB causes the crystal to become self-frequency-doubling (SFD) material. The synthesis and crystal growth of Nd x Gd 1− x COB are reported in this paper. The polarized transmittance spectra and fluorescence spectra were measured at room temperature. The strong emission peaks in the range of 850–950xa0nm are reported for the first time for the Nd x Gd 1− x COB crystal. The ( θ =66.8°, φ =132.6°) phase-matching direction was reported for the first time as the optimum phase-matching direction at 1060xa0nm by calculation and experiments whose d eff was measured and found to be 2.1xa0pm/v. The SFD experiments were carried out on 3×3×7xa0mm 3 sample with (66.8°, 132.6°) direction. The green output power at 530.5xa0nm was 192xa0mW when pumped by 1600xa0mW Tixa0:xa0sapphire tuned to 811xa0nm. The threshold was 16xa0mW. The optical–optical conversion efficiency was 12%.

Passively Q-switched self-frequency-doubling Nd3+:GdCa4O(BO3)3 laser with GaAs saturable absorber

Nd 3 + :GdCa 4 O(BO 3 ) 3 , i.e., Nd:GdCOB, is a new self-frequency-doubling laser crystal. By using a GaAs saturable absorber as a passive Q-switched, the Q-switched Nd:GdCOB laser at 0.53 μm is successfully realized. Meanwhile, the pulse width and the single pulse energy are measured and the numerical solutions of the coupling wave rate equations are in agreement with the experimental results.

Studies on the effective nonlinear coefficient of GdCa4O(BO3)3 crystal

Abstract Large-sized and optical-quality GdCa4O(BO3)3 (GdCOB) crystal can be grown from melt by CZ pulling method. GdCOB is transparent in the range of 320–2600xa0nm. Second-harmonic-generation (SHG) experiments were carried out on the samples along ( θ=90° , φ =46°) phase-matching (PM) direction in the XY -main plane and (66.8°,xa047.4°), (66.8°,xa0132.6°) PM directions out of the main planes, respectively. The SHG conversion efficiency of an 8xa0mm long sample along (66.8°,xa0132.6°) PM direction was larger than 33% at 31xa0mJ input energy by a Q -switched Ndxa0:xa0YAG laser, which is the best result obtained so far to the best of our knowledge. The d eff of these PM directions were estimated by comparing the conversion efficiency with that of KTP crystal. (66.8°,xa0132.6°) PM direction whose d eff is 2.1xa0pm/v was reported for the first time as the optimum PM direction in GdCOB crystal. The angular acceptance and walk-off for these different directions were calculated, which shows GdCOB has a small walk-off and a large angular acceptance.

Growth and properties of NaEr(WO4)2 crystals

Abstract Tetragonal scheelite-like single crystals NaEr(WO 4 ) 2 (NEW) have been grown by using RF-heating Czochralski (CZ) method for the first time. X-ray powder diffraction experiments show that the crystal has the same structure as NaY(WO 4 ) 2 (NYW) and its unit cell parameters were calculated as a=b =0.5199 nm , c =1.1265 nm , and V =0.3045 nm 3 . Differential scanning calorimetry shows that the NEW crystal melts at 1188.5°C, which is lower than that of NYW crystal. Optical properties measurements show that NEW has intensive green luminescence emission at 551xa0nm pumped by LD with a wavelength of 974xa0nm, which is a potential for green laser emission running through up-conversion.

Growth of a new ordered langasite structure compound Ca3TaGa3Si2O14 single crystal

Abstract A newly ordered piezoelectric single crystal Ca 3 TaGa 3 Si 2 O 14 (CTGS) with langasite structure had been successfully grown with the dimensions of 16–14xa0mm in diameter and 37xa0mm in length using the Czochralski technique. The X-ray powder diffraction (XRPD) of different parts of the single crystal was performed at room temperature. Lattice parameters had been computed from single crystal XRPD peak values. The composition of the grown crystal had been studied by X-ray fluorescence analysis. Differential thermal analysis and thermal gravity analysis had been carried out and found that the CTGS crystal started to melt at 1185°C and the peak was at 1368°C.

Growth and noncritical phase-matching third-harmonic-generation of GdxY1−xCa4O(BO3)3 crystal

Abstract A series of solid-solution crystals Gd x Y 1− x Ca 4 O(BO 3 ) 3 (Gd x Y 1− x COB) ( x =0–1) were grown by the Czochralski (CZ) method. The distribution coefficients of Gd 3+ and Y 3+ ions in Gd x Y 1− x COB crystal are 0.952 and 1.069, respectively, which were measured by X-ray fluorescent analysis. So Y 3+ ions are easier to incorporate into Gd x Y 1− x COB crystal lattice than Gd 3+ ions. The composition of crystal from the seed to the bottom is homogeneous. The noncritical phase-matching (NCPM) third-harmonic generation (THG) of Ndxa0:xa0YAG laser (1064xa0nm) can be realized in Gd 0.37 Y 0.63 COB crystal along the Y-principal axis. The UV cutoff of Gd 0.37 Y 0.63 COB is at 320xa0nm when measured by HITARCHI U-3500 spectrophotometer. For the first time, THG experiments of Gd 0.37 Y 0.63 COB crystal were performed using Q-switched Ndxa0:xa0YAG laser. The output energy is up to 88.2xa0mJ at 355xa0nm when the input energy is 600xa0mJ for 11xa0mm long Gd 0.37 Y 0.63 COB crystal. The THG optical–optical conversion efficiency of Gd 0.37 Y 0.63 COB crystal is 14.7%.

Phonon-assisted mechanisms and concentration dependence of Tm3+ blue upconversion luminescence in codoped NaY(WO4)2 crystals

Optical parameters of NaY(WO4)2 crystals were calculated from absorption spectra with Judd–Ofelt theory. Intensive infrared-to-visible frequency upconversion has been discovered and investigated under a 974 nm CW laser diode excitation at room temperature. The bright blue upconversion fluorescence emission is analysed in detail. The optimal concentration of Tm3+, which is about 1 at% for a Yb3+ concentration of 10 at% for the blue emission in the crystals, is much higher than that in other hosts. The experimental results and theoretical analysis suggest that NaY(WO4)2 with high phonon energy is most probably an even more promising crystal than fluoride.

Characteristics of a passively Q-switched Nd3+:NaY(WO4)2 laser with Cr4+:YAG saturable absorber

Abstract By using xenon flash lamp as pump source and Cr4+:YAG as passive Q-switcher, we have performed the Q-switched laser operation at 1.06 μm with an Nd3+:NaY(WO4)2 (known as Nd:NYW) crystal. Meanwhile, the pulse width, the single pulse energy and the repetition rate under different small-signal transmissions of Cr4+:YAG and different reflectivities of output reflector are measured, and the numerical solutions of the coupling wave rate equations agree with the experimental results.

Effect of Nd3+ concentration on the laser performance of a new laser crystal: Nd : NaY(WO4)2

Abstract We have measured the transmission and emission spectra of a new crystal, Ndxa0:xa0NaY(WO 4 ) 2 (Ndxa0:xa0NYW). Using a Tixa0:xa0sapphire laser as the pump source, the laser performances of Ndxa0:xa0NYW crystals with different concentrations are compared for the first time. The Nd 3+ concentrations used are 1, 2, 4 and 5xa0at%. Our investigation shows that 2xa0at% is the optimum concentration. When the incident pump power is 575xa0mW, the 1.06xa0μm output can reach 184xa0mW, corresponding to an optical-to-optical efficiency of 32%. We believe that our work is significant for the further research and actual application of this promising laser crystal.

Laser characteristics of Cr:Nd:GdCOB self-frequency-doubling crystal

The phase matching angle of GdCOB crystal is calculated. By using Xenon flash lamp as pump source, we have realized the free run from 1.06 μm to 0.53 μm in self-frequency-doubling Cr:Nd:GdCOB (bi-doped) crystal and Nd:GdCOB (uni-doped) crystal. The experimental results show that the threshold energies for bi-doped crystal and uni-doped crystal are 0.92 J and 1.00 J, respectively; when the pump energy is 10 J, the output energies of green laser for two kinds of crystals are 2.46 mJ and 1.96 mJ, respectively. The output energy of Cr:Nd:GdCOB crystal has an increase of 25% in comparison to that of Nd:Gd:COB crystal. In addition, we discuss ways to improve efficiency.