Hu Guoqing, Mizuguchi Tatsuya, Oe Ryo, Nitta Kazuki, Zhao Xin, Minamikawa Takeo, Li Ting, Zheng Zheng, Yasui Takeshi
Graduate School of Advanced Technology and Science, Tokushima University, 2-1, Minami-Josanjima, Tokushima, Tokushima, 770-8506, Japan.
School of Electronic and Information Engineering, Beihang University, 37 Xueyuan Rd., Beijing, 100191, China.
Sci Rep. 2018 Jul 24;8(1):11155. doi: 10.1038/s41598-018-29403-9.
Dual terahertz (THz) comb spectroscopy enables high spectral resolution, high spectral accuracy, and broad spectral coverage; however, the requirement for dual stabilized femtosecond lasers hampers its versatility. We here report the first demonstration of dual THz comb spectroscopy using a single free-running fibre laser. By tuning the cavity-loss-dependent gain profile with an intracavity Lyot filter together with precise management of the cavity length and dispersion, dual-wavelength comb light beams with slightly detuned repetition frequencies are generated in a single laser cavity. Due to sharing of the same cavity, such comb light beams suffer from common-mode fluctuation of the repetition frequency, and hence the corresponding frequency difference between them is passively stable around a few hundred hertz within millihertz fluctuation. While greatly reducing the size, complexity, and cost of the laser source by use of a single free-running fibre laser, the dual THz comb spectroscopy system maintains a spectral bandwidth and dynamic range of spectral power comparable to a system equipped with dual stabilized fibre lasers, and can be effectively applied to high-precision spectroscopy of acetonitrile gas at atmospheric pressure. The demonstrated results indicate that this system is an attractive solution for practical applications of THz spectroscopy and other applications.
双太赫兹（THz）梳状光谱能够实现高光谱分辨率、高光谱精度和宽光谱覆盖范围；然而，对双稳飞秒激光器的要求限制了其通用性。我们在此报告了首次使用单个自由运转光纤激光器进行双太赫兹梳状光谱的演示。通过使用腔内Lyot滤波器调节与腔损耗相关的增益分布，并精确控制腔长和色散，在单个激光腔内产生了重复频率略有失谐的双波长梳状光束。由于共享同一个腔，此类梳状光束会受到重复频率的共模波动影响，因此它们之间相应的频率差在毫赫兹波动范围内被动稳定在几百赫兹左右。双太赫兹梳状光谱系统在使用单个自由运转光纤激光器极大地减小了激光源的尺寸、复杂性和成本的同时，保持了与配备双稳光纤激光器的系统相当的光谱带宽和光谱功率动态范围，并且能够有效地应用于大气压下乙腈气体的高精度光谱分析。所展示的结果表明，该系统是太赫兹光谱实际应用及其他应用的一个有吸引力的解决方案。
