Piezo-locking a diode laser with saturated absorption spectroscopy

We demonstrate modulation-based frequency locking of an external cavity diode laser, utilizing a piezo-electrically actuated mirror, external to the laser cavity, to create an error signal from saturated absorption spectroscopy. With this method, a laser stabilized to a rubidium hyperfine transition has a FWHM of 130 kHz over seconds, making the locked laser suitable for experiments in atomic physics, such as creating and manipulating Bose-Einstein condensates. This technique combines the advantages of low-amplitude modulation, simplicity, performance, and price, factors that are usually considered to be mutually exclusive.