Using our cavity-enhanced frequency modulation technique, we obtained the saturated signal of the weakly absorbing gas C2HD for the P(5) line of the (ν2 + 3ν3) overtone band at 1.064 µm. An absorption sensitivity of 1.2 × 10-10 (1.8 × 10-12/cm) has been obtained. The absolute frequency of the line center is established (within ±2.6 kHz) with respect to a doubled Nd:YAG laser/I2 frequency reference. The short-term stability, limited by the available signal-to-noise ratio, currently is 1 + 10-11 at 1 s, improving to 5 × 10-13 at 1000 s. The measured pressure-broadening rate is 34.7(0.8) kHz/mTorr (260 ± 6.1 kHz/Pa). Selection of slow molecules gave a linewidth four times narrower than the room-temperature transit-time limit.
© 1996 Optical Society of America
Jun Ye, Long-Sheng Ma, and John L. Hall, "Sub-Doppler optical frequency reference at 1.064 µm by means of ultrasensitive cavity-enhanced frequency modulation spectroscopy of a C2HD overtone transition," Opt. Lett. 21, 1000-1002 (1996)