Automatic locking of a 633 nm semiconductor laser on iodine

The purpose of this paper is to develop a low-cost semiconductor laser frequency standard around 633 mm based on digital signal processing techniques. This standard sweeps the frequency of the laser by means of the injection current in order to measure some linear absorption transitions of iodine (¹²⁷I₂). It identifies those lines by using a reference table of known transitions of the iodine vapor and then automatically locks the frequency of the laser on a selected transition. A microcontroller and a digital signal processor are used to perform those functions. The effects of laser temperature, mode jumps, and transition linewidth are considered for successful operations. It is demonstrated that this system can automatically lock a 633 nm semiconductor laser on the P(33) 6-3 transition of iodine