Modulation-free portable laser frequency and power stabilization system

Abstract

The performance of laser-based instruments heavily depends on the stability of their laser source. Some instruments, such as the Cs–4He magnetometer, even require the frequency stabilization and the power stabilization at the same time. In this work, we design a double-locking system with a fiber-coupled output on a small bread board and apply it to the pump laser of a Cs–4He magnetometer. By carefully choosing the stabilization methods, we significantly improve the long-term simultaneous stability of frequency and power of the pump laser. The laser frequency drifts in 2 h are reduced from 100 to 10 MHz. For 10 h continuous measurements, their Allan deviation obtains about two orders of magnitude improvement for the averaging time larger than 200 s and reaches σ( τ) = 1.57 × 10−9 with a 200 s averaging time. The laser power stability for 1.8 h also obtains two orders of magnitude improvement from 3.22% to 0.031%, and its power noise reaches a level that is very close to the electronic noise of the detector. Applying this stabilization system to the pump laser of a fiber-coupled Cs–4He magnetometer, its magnetic sensor noise is significantly reduced from 0.158 to 0.009 nT, which is a reasonable noise for magnetic field detection. With this on-board design of the laser stabilization system, it is more convenient to transform the magnetometer into an outdoor device.