Uchida Hirohisa, Kawauchi Tetsuya, Otake Gemma, Koyama Chisa, Takeya Kei, Tripathi Saroj R
ARKRAY Inc., Kamigyo-ku, Kyoto, 602-0008, Japan.
Department of Electronics, Nagoya University, Nagoya, Aichi, 464-8603, Japan.
Sci Rep. 2022 Sep 5;12(1):15082. doi: 10.1038/s41598-022-17893-7.
In the process of terahertz (THz) wave generation via optical rectification of infrared femtosecond pulses in a non-linear optical crystal, the power of terahertz wave is directly proportional to the square of the optical pump power. Therefore, high power terahertz wave can be generated using a high power femtosecond laser provided that the crystal has both high laser induced damage threshold and optical non-linear coefficient. However, a significant amount of pump power is lost in this process due to the Fresnel's reflection at the air-crystal boundary. In this paper, we numerically and experimentally demonstrate that the coat of optical thin film called Cytop on the 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) crystal effectively reduces the reflection loss of pump power, thereby increasing the THz wave emission efficiency of the DAST crystal. We found that the average power of THz wave emitted by the thin film coated crystal is about 28% higher than the THz power emitted by the uncoated crystal when an equal amount of laser power is used. The thin film coated DAST crystals can be used not only in terahertz measurement systems but also in optical devices such as modulators and waveguides.
在通过非线性光学晶体中红外飞秒脉冲的光学整流产生太赫兹（THz）波的过程中，太赫兹波的功率与光泵浦功率的平方成正比。因此，只要晶体具有高激光损伤阈值和光学非线性系数，就可以使用高功率飞秒激光产生高功率太赫兹波。然而，由于在空气 - 晶体边界处的菲涅尔反射，在此过程中会损失大量的泵浦功率。在本文中，我们通过数值和实验证明，在4 - N，N - 二甲基氨基 - 4'- N'- 甲基 - 二苯乙烯基甲苯磺酸盐（DAST）晶体上涂覆名为 Cytop 的光学薄膜，可有效降低泵浦功率的反射损耗，从而提高 DAST 晶体的太赫兹波发射效率。我们发现，当使用等量激光功率时，涂覆薄膜的晶体发射的太赫兹波平均功率比未涂覆晶体发射的太赫兹功率高约28％。涂覆薄膜的 DAST 晶体不仅可用于太赫兹测量系统，还可用于调制器和波导等光学器件。
