2.1-microm lasers frequency stabilized against CO2 lines: comparison between fringe-side and frequency-modulation locking methods.

A comparison between the use of the fringe-side and the frequency-modulation methods to frequency stabilize diode-pumped Tm-Ho:YAG lasers against linear absorption lines of CO2 near 2.1 microm is reported. Frequency stability was evaluated by monitoring of the beat signal between two independently stabilized Tm-Ho:YAG systems. Frequency instability levels of approximately 20 and approximately 400 kHz for 1-s integration time were achieved by the frequency-modulation and fringe-side methods, respectively.