Stabilization of a 2.1 mu m diode-pumped Tm-Ho : YAG laser against linear transitions of CO2

Absolute frequency stabilization of 2.1 mum diode-pumped Tm-Ho:YAG lasers at 2.1 mum is reported. Different rotovibrational absorption lines of CO2 were used as absolute frequency references. The frequency control of a custom made, single-frequency and tunable Tm-Ho:YAG lasers was achieved by means of two linear spectroscopy methods: the fringe-side locking method and the wavelength modulation technique. Comparison between the experimental results obtained using these two methods is also reported. With both locking methods a significant improvement of the laser frequency stability was obtained. In particular a minimum value of frequency stability of 20 kHz at 1 s integration time was achieved using the wavelength modulation method, whereas for the fringe-side technique a minimum stability of 100 kHz was obtained for an integration time of 10 ms. The achieved stability levels are more than one order of magnitude better than typical Doppler-Lidar system requirements.