Highly sensitive cavity-enhanced sub-Doppler spectroscopy of a molecular overtone band with a 1.66 mu m tunable diode laser

Sensitive sub-Doppler resolution molecular spectroscopy developed by Hall a nd co-workers [J. Opt. Soc. Am. B 15 (1998) 6] has been applied to the 1.66 mu m region using a widely tunable external-cavity diode laser. We have re corded saturated absorption spectra of the 2 upsilon(3) vibrational overton e band of methane with a sensitivity of 9.5 x 10(-11) cm(-1) st a time cons tant of 1.25 s and a spectral linewidth of 320 kHz (full width at half maxi mun; FWHM) over the tunable range of 1.63 to 1.68 mu m.