External cavity diode laser with long-term frequency stabilization based on mode boundary detection

We have implemented a long-term frequency stabilization system for external cavity diode laser (ECDL) based on mode boundary detection method. In this system, the saturated absorption spectroscopy was used. The current and the grating of the ECDL were controlled by a computer-based feedback control system. By checking any mode boundaries in the spectrum, the control system determined how to adjust current to avoid mode hopping. This procedure was executed periodically to ensure the long-term stabilization of ECDL in the absence of mode hops. This laser diode system without antireflection-coating had over operated in the condition of long-term mode hopping free stabilization for almost 400 hours. Last year, we have added template matching technics to the system. The ECDL stabilization time has been extended to almost 1200 hours without any manual intervention further. This is a significant improvement of ECDL frequency stabilization system. This technique is very useful in some applications such as laser atomic cooling and atom fountain etc.