A highly sensitive photoacoustic spectrometer for near infrared overtone

By optimizing the size of a photoacoustic cell for decreasing acoustic loss and noise, and using a proper multipass arrangement for increasing light power in the cell and optical coupling to the acoustic wave, a high-resolution external laser photoacoustic spectrometer with a detection sensitivity of 6.35 × 10^-9 cm^-1 (1:1 signal to noise level) has been developed. Using this apparatus, the high quality Doppler-limited overtone spectra of AsH₃ (600) and H₂Se (60) have been observed at room temperature in the wave number regions 11 500-11 650 and 12 600-12 925 cm^-1, respectively. Results are presented which highlight the applicability of this apparatus to the spectroscopy of weak optical transitions.