We report the measurement of the frequency noise power spectral density (PSD) of a Terahertz (THz) molecular laser (ML) pumped by a mid-infrared (MIR) quantum cascade laser (QCL), and emitting 1 mW at 1.1THz in continuous wave. This is achieved by beating the ML frequency with the 1080th harmonic of the repetition rate of a 1560 nm frequency comb (FC). We find a frequency noise PSD < 10Hz2/Hz (-95dBc/Hz) at 100kHz from the carrier. To demonstrate the effect of the stability of the pump laser on the spectral purity of the THz emission we also measure the frequency noise PSD of a CO2-laser-pumped 2.5THz ML, reaching 0.1Hz2/Hz (-105dBc/Hz) at 40kHz from the carrier, limited by the frequency noise of the FC harmonic. Finally, we show that it is possible to actively phase-lock the QCL-pumped molecular laser to the FC repetition rate harmonic by controlling the QCL current, demonstrating a sub-Hz linewidth.

中文翻译：

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量子级联激光泵浦太赫兹分子激光器：频率噪声和使用1560 nm频率梳的锁相。

我们报告了由中红外（MIR）量子级联激光器（QCL）泵浦并在1.1THz连续发射1 mW的太赫兹（THz）分子激光器（ML）的频率噪声功率谱密度（PSD）的测量结果波。这是通过以1560 nm频率梳（FC）的重复频率的1080次谐波击败ML频率来实现的。我们发现距载波100kHz处的频率噪声PSD <10Hz2 / Hz（-95dBc / Hz）。为了证明泵浦激光器的稳定性对THz发射光谱纯度的影响，我们还测量了CO2激光泵浦的2.5THz ML的频率噪声PSD，在40kHz时达到0.1Hz2 / Hz（-105dBc / Hz）来自载波的信号受到FC谐波频率噪声的限制。最后，