Al、S和Te掺杂GaSe晶体的光学及倍频特性

Optical and Second Harmonic Properties in Al,S and Te Doped GaSe Crystals

对不同浓度Al、S和Te掺杂GaSe晶体的透过率和倍频特性进行了研究.结果表明,适宜浓度的掺杂晶体在透明波段内吸收系数约为α≤0.1-0.2cm-1,适于非线性应用.GaSe∶S晶体透过率曲线向短波方向移动,且更适于高浓度掺杂,而Al和Te掺杂晶体透明范围的波段截止波长向长波方向移动,且移动幅度小于S掺杂晶体,当掺杂浓度达到GaSe∶Al（0.5mass%）和GaSe∶Te（5mass%）时,晶体光学质量明显下降.通过fs Ti∶Sapphire激光和CO2激光泵浦下I类倍频实验发现,S掺杂晶体相位匹配曲线向短波方向移动,倍频输出功率比纯GaSe晶体有明显提高,最佳掺杂浓度为2mass%.Al和Te掺杂晶体相位匹配角与纯GaSe晶体相比没有明显变化,实验结果与理论曲线符合较好.利用非线性方法研究发现当掺杂浓度不超过5mass%时,GaSe∶Te晶体与纯GaSe同样属于六角形结构.三种掺杂方式最佳掺杂浓度分别为GaSe∶Al（0.1mass%）,GaSe∶S（2mass%）和GaSe∶Te（0.5mass%）,在CO2激光泵浦下,三者频率转换效率之比约为1∶0.6∶0.5.在所使用的晶体样本中,GaSe∶S（2mass%）晶体性能最佳,其频率转换效率可达纯GaSe晶体的3倍左右.

The transparency and second harmonic properties of Al,S and Te doped GaSe crystals were studied.Low absorption coefficients ofα≤0.1~0.2cm-1 are found in crystals with suitable doping level in transparent range which can be used in nonlinear devices.High doping level is allowed in GaSe∶S crystals whose transparency spectra shift towards to short-wavelength range.The short wavelength transparency cut-off of both Al and Te doped crystals shifts more slowly than S doped crystals towards to opposite direction. The optical quality of the crystals has declined markedly when the doping concentration up to GaSe∶Al（0.5mass%）and GaSe∶Te（5mass%）.The phase matching curves shift towards to short-wavelength and output power is significantly higher in S doped GaSe crystals than that in pure GaSe crystals with fs Ti∶Sapphire laser and CO2 laser pumping.The optimal doping concentration is ascertained as 2 mass%.No obvious differences of type I second harmonic phase matching angle between Al,Te doped and pure crystals are found.The experimental results are in good agreement with theoretical curve.GaSe∶Te crystals are found to possess the hexagonal structure likeε-GaSe when the doping concentration is no more than 5mass% with nonlinear method.The SHG efficiency ratio of the optimal doped crystals GaSe∶Al（0.1mass%）,GaSe∶S（2mass%）and GaSe∶Te（0.5mass%）isabout 1∶0.6∶0.5under CO2 laser pumping.GaSe∶S（2mass%）crystal shows the best performance whose efficiency is about 3times higher than that in pure GaSe among all used samples.