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Journal of Undergraduate Research

Keywords

measuring frequency noise, mode hops, extended cavity diode lasers

College

Physical and Mathematical Sciences

Department

Physics and Astronomy

Abstract

Diode lasers are useful in physics because they are relatively cheap and robust, they are available in a number of wavelengths, and they are tunable. However, because diode lasers have large bandwidths compared to atomic resonances, a reflection grating is added outside the laser. This creates the extended cavity in extended cavity diode lasers (ECDLs) and forces the lasers to operate at a narrower line width, one acceptable for use in atomic physics. Unfortunately, because the ECDL has many factors trying to control the wavelength of the laser (e.g. temperature, current, grating angel and position) small changes in the lasers environment can cause it to mode hop. Passive control, such as precisely controlling the current and the temperature, can prevent changes in the environment and prevent mode hops, but ECDLs with very good passive control are expensive and even the best made lasers will eventually drift and mode hop. A better option is some form of active control. We believe we can use frequency noise to predict and prevent mode hops. I have demonstrated that the frequency noise on the laser increases before a mode hop. I have also designed and built a filtering circuit to measure the amount of frequency noise on the laser to use as error signal the move the laser to a stable environment.

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