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分别利用1kHz和200kHz两种重复频率的近红外飞秒激光,经过低数值孔径的物镜聚焦,空间选择性地辐照KCl晶体,在KCl晶体内部诱导出了一系列色心缺陷。通过飞秒激光辐照前后KCl晶体的吸收光谱分析,明确了飞秒激光照射后KCl晶体内部5种色心的归属,发现色心的浓度随着飞秒激光功率的升高而增长。对吸收光谱的分析表明,两种重复频率的飞秒激光所诱导的色心吸收带相应的峰值略有偏移。认为这是由高重复频率的飞秒激光的热累积效应引起的。理论分析表明,KCl晶体内部的点缺陷和高功率密度飞秒激光与KCl晶体相互作用所诱导的多光子吸收是色心形成的主要原因。
The near-infrared femtosecond laser with two kinds of repetition frequencies of 1kHz and 200kHz respectively was used to irradiate KCl crystal spatially selectively through low numerical aperture objective lens. A series of color center defects were induced in KCl crystal. By analyzing the absorption spectra of KCl crystals before and after femtosecond laser irradiation, the ownership of 5 kinds of color centers in KCl crystal after femtosecond laser irradiation was clarified. The concentration of color centers increased with the increase of femtosecond laser power. The analysis of the absorption spectra shows that the corresponding peak of the color center absorption band induced by the femtosecond laser of two repetition frequencies slightly shifts. This is thought to be caused by the heat accumulation effect of the high-repetition rate femtosecond laser. Theoretical analysis shows that the multi-photon absorption induced by the point defect in KCl crystal and the interaction between high power density femtosecond laser and KCl crystal is the main reason for the formation of color center.