【摘要】 窄线宽激光由于其具有单色性好、稳定度高、相干长度长等优点,广泛应用于光电检测领域,包括相干通信、精密测量、光学频率标准、吸收光谱计量以及光与物质相互作用研究等。目前频率稳定的氦氖激光器线宽可以达到MHz量级,分布反馈式（DFB）光纤激光器线宽可达kHz量级, DFB半导体激光器线宽可以达到MHz量级,然而光栅反馈半导体激光器可以实现百kHz量级线宽的输出。为了进一步压窄各类激光器线宽,需要通过反馈控制技术来锁定激光到某一频率参考。该研究将自行设计的超稳腔作为频率参考,实现了632.8 nm外腔半导体激光器（ECDL）线宽的有效压窄。本窄线宽激光产生系统的研制包括超稳腔设计、光路设计、 ECDL频率控制以及系统集成。超稳腔采用两镜法布里-珀罗腔（F-P腔）结构,腔体是膨胀系数约为10^-6 K^-1的微晶玻璃,腔镜为一对反射率达99.988 5%（±0.003 5%）的平面镜和凹面镜。为进一步减小外界环境对F-P腔腔长的影响,需要对腔体进行温度控制,本系统采用四片总功率为96 W的半导体制冷片以及水冷散热设计。同时为了降低声音和空气流动对腔模频率的影响,将F-P腔置于真空度为10^-5 torr的真空室中;另外为了有效隔振,腔体与真空室用硅橡胶材料隔离。该系统采用的ECDL为德国Toptica公司的DL pro系列激光器,其具有压电陶瓷（PZT）和电流调制两个频率控制端,响应带宽分别为1 kHz和100 MHz。激光器的频率控制采用了Pound-Drever-Hall （PDH）锁频技术, 18 MHz的调制频率加载到激光器的电流调制端,通过对F-P腔的反射信号进行解调获得误差信号,通过两路反馈控制,实现了近1 MHz的锁定带宽。通过对系统的不断优化,最后将自由运转状态下约300 kHz的激光线宽压窄到了10 kHz量级,并且系统运行稳定,连续12小时锁定的频率漂移量约为30 MHz。该研究研制的632.8 nm窄线宽激光源不仅可以应用到吸收光谱计量领域,同时也可以在光学面型精密测量领域发挥重要作用。更多还原

【Abstract】 Narrow linewidth lasers are widely used in the field of optoelectronic detection due to their advantages such as good monochromaticity, high stability, and long coherence length, including coherent communication, precision measurement, optical frequency standards, absorption spectrum measurement, and research on the interaction between light and matter. At present, the linewidth of stable He-Ne lasers can reach the order of MHz. The linewidth of distributed feedback（DFB） fiber lasers can reach the order of kHz. The linewidth of DFB semiconductor lasers can also reach the order of MHz. However, grating feedback semiconductor lasers can achieve Hundreds of kHz line width output. In order to further narrow the line width of various lasers, it is necessary to lock the laser to a certain frequency reference through feedback control technology. In this paper, a self-designed ultra-stable cavity is used as the frequency reference, and the effective narrowing of the linewidth of 632.8 nm external cavity semiconductor laser（ECDL） is achieved. The narrow linewidth laser generation system includes the design of an ultra-stable cavity, the design of the optical path, the frequency control of ECDLand the integration of the system. The super-stable cavity adopts a two-mirror Fabry-Perot cavity（F-P cavity） structure, and the cavity is glass-ceramic with an expansion coefficient of about 10^-6 K^-1. The cavity mirror is a pair of flat and concave mirrors with a reflectivity of 99.988 5%±0.003 5%. In order to reduce the influence of the external environment on the cavity length of the FP cavity, the temperature of the cavity needs to be designed. This system uses four peltiers with a total power of 96 W and a water-cooled heat dissipation design. In order to reduce the influence of sound and air flow on the cavity mode frequency, the F-P cavity is placed in a vacuum chamber with a vacuum of 10^-5 torr. For effective vibration isolation, the cavity is isolated from the vacuum chamber with a silicone rubber material. The ECDL used by this system is the DL pro series laser from German Toptica Company, which has two frequency control terminals of piezoelectric（PZT） and current modulation, and the response bandwidth is 1 kHz and 100 MHz respectively. The frequency control of the laser uses Pound-Drever-Hall（PDH） frequency locking technology. The modulation frequency of 18 MHz is loaded on the current modulation terminals of the laser. The error signal is obtained by demodulating the reflected signal of the FP cavity. Through two-way feedback control, a locked bandwidth of nearly 1 MHz is achieved. Through continuous optimization of the system, we finally narrowed the laser line width of about 300 kHz in the free-running state to the order of 10 kHz, and the system operated stably, and the frequency drift locked for 12 hours was about 30 MHz. The 632.8 nm narrow linewidth laser source developed in this paper can not only be applied to the field of absorption spectrum measurement, but also play an important role in the field of optical surface precision measurement.更多还原