面向空间引力波探测的毫赫兹频段低强度噪声单频激光器  

Millihertz band low-intensity-noise single-frequency laser for space gravitational wave detection

作　　者：王在渊 王洁浩 李宇航 柳强[1,2] Wang Zai-Yuan;Wang Jie-Hao;Li Yu-Hang;Liu Qiang(Department of Precision Instrument,Tsinghua University,Beijing 100084,China;Key Laboratory of Photonic Control Technology,Ministry of Education,Tsinghua University,Beijing 100084,China;Ordnance Sergeant College of Army Engineering University,Wuhan 430075,China)

机构地区：[1]清华大学精密仪器系,北京100084 [2]清华大学,光子测控技术教育部重点实验室,北京100084 [3]陆军工程大学军械士官学校,武汉430075

出　　处：《物理学报》2023年第5期142-148,共7页Acta Physica Sinica

基　　金：国家重点研发计划(批准号:2020YFC2200403)资助的课题。

摘　　要：低噪声单频激光器是空间引力波探测系统中的核心器件,其噪声性能直接影响空间引力波探测器的灵敏度.本文报道了一种面向空间引力波探测的低噪声单频激光器,利用全保偏光纤结构的功率放大器对低功率、窄线宽、低噪声的非平面环形振荡器输出激光进行放大.为降低激光的强度噪声,比较了不同泵浦源的输出特性,为光纤放大器选用波长锁定的泵浦源,降低泵浦光波长随温度漂移对输出功率的影响,利用光电负反馈控制技术抑制输出激光的强度噪声,结合主动精确控温技术抑制关键器件的热噪声,实现了毫赫兹频段强度噪声的抑制.利用自主搭建的4通道相对强度噪声测量系统,测得反馈控制后的激光器相对强度噪声在1 mHz—1 Hz频段内低于-60 dBc/Hz,在1 mHz和1 Hz处分别为-63.4 dBc/Hz和-105.8 dBc/Hz.研究结果表明,通过放大器泵浦电流的反馈控制和关键器件的温度控制可以有效地抑制激光器在毫赫兹频段的强度噪声,为进一步提高低频段强度噪声性能奠定基础.A low-noise single-frequency laser is a key component of the space-based gravitational wave detector,and the intensity noise of the laser directly affects the sensitivity of the space-based GW detector.In this work,we report a low-noise single-frequency laser designed for space-based gravitational wave detector.The laser is based on a master oscillator power amplifier(MOPA),which is designed to possess a low-power,narrow-linewidth seed laser acting as master oscillator(MO) and an all polarization-maintaining fiber amplifier acting as power amp lifier(PA).The amplifier that uses a robust mechanical design consists of an Yb-doped double-clad fiber forward pumped by wavelength-locked 976 nm pump laser diode(LD) to achieve 2.13 W of output power and 70 dB of signal-noise ratio(SNR).To suppress the relative intensity noise(RIN) in a millhertz regime(1 mHz-1 Hz),we characterize the power stabilization of a pump diode laser based on a proportional-integral-derivative(PID)feedback control loop where an in-loop photodetector is used.The power fluctuation can be converted into the fluctuation of the current signal by the photodiode,the current signal is converted into the voltage signal and amplified by a transimpedance circuit.Then,the voltage signal is compared with the voltage reference signal,and the error signal is achieved to adjust real-timely the drive current of the pump laser diode.This is a good way to significantly suppress the RIN of a laser at low frequencies,but the measured RIN below 4 mHz is still higher than-60 dBc/Hz.In order to further suppress the RIN to lower than 4 mHz,an active precise temper ature control technology is used to suppress the thermal noise from pump LD and fiber coupler.To assess the RIN milliertz regime,we design an RIN measurement system consisting of a high-precision signal acquisition card(24 bit) and a computer program based on Lab VIEW.The measurement range of the system is 2 μHz-102.4 kHz and the frequency resolution up to 2 μHz,much better than the counterparts of commercial

关 键 词：单频激光器 毫赫兹频段 相对强度噪声 光电负反馈 

分 类 号：P111[天文地球—天文学] P142.84[电子电信—物理电子学] TN248