基于光学参量振荡器的可调谐红外激光的强度噪声特性

Intensity noise of tunable infrared laser based on singly resonant optical parametric oscillator

红外激光光源在微量气体、高分辨率光谱分析和量子光学研究等领域具有重要的应用.本文利用锁定单共振光学参量振荡器内腔标准具的方案获得了无跳模连续调谐的红外激光输出,理论和实验研究了红外激光的强度噪声特性,分析了影响强度噪声的因素.通过控制非线性晶体的温度和标准具调制信号实现了对红外激光强度噪声的抑制.当控制非线性晶体工作温度为60℃,内腔标准具调制信号为8 kHz时,单共振光学参量振荡器输出信号光和闲置光的强度噪声分别降低了11和8 dB.

The infrared laser sources have important applications in many fields such as real-time detection, gas sensing or tracing, high-resolution spectral analysis and quantum optics. In this paper, we develop an infrared laser source with mode-hop-free broadband tunability by using a singly optical parametric oscillator(SRO)based on the magnesium-oxide doped periodically poled lithium niobite(MgO:PPLN) crystal. A polished lithium niobite crystal with a thickness of 1 mm is used as an etalon that is inserted into the cavity of SRO to realize continuous mode-hop-free tuning. The resonant signal in SRO is frequency stabilized to the transmission peak of intracavity etalon. Owing to the high stability of the resonator, continuous mode-hop-free tuning with a bandwidth of 2063.7 GHz for both signal and idler is realized. The oscillation threshold of SRO is 7.3 W. The signal of 4.3 W over 1551.9-1568.6 nm and idler of 2.1 W over 3307.3-3384.3 nm are generated for 22 W of pump power by tuning the temperature of the crystal from 20 ℃ to 70 ℃. The slope efficiency of 42.6% and optical conversion efficiency of 29% are obtained. Then the intensity noise characteristics of generated infrared laser are further studied theoretically and experimentally. The fluctuation characteristics of the SRO emission can be computed just by using a semiclassical approach. We analyze theoretically the factors that affect the intensity noise of the signal and idler. The temperature of the MgO:PPLN crystal and the modulation frequency of the etalon are important parameters, which can affect the intensity noise characteristics of signal and idler laser. Therefore, we investigate experimentally the variation of the intensity noise characteristics by changing the temperature of the crystal and the modulation frequency of the etalon. The intensity noise of the signal and idler laser are optimized through controlling the temperature in a range of 20-60 ℃ and the modulation frequency ranging from 2 kHz to 8 kHz, respectively. The experimental data basically accord with the theoretical calculations. When the operating temperature of the MgO:PPLN crystal is controlled at 60 ℃ and the modulation frequency of the etalon is 8 kHz, the intensity noise of the signal and the idler laser are reduced by 11 dB and 8 dB, respectively. The optimized infrared laser can provide a high-quality laser source for subsequent quantum optics research.