Compact Resonance Π-Shaped Photoacoustic Cell for Gas Detection

A compact resonance photoacoustic cell with a Π-shaped internal cavity and a volume of ~0.2 cm3 is developed. The design of the cell and an experimental setup for testing its operational capabilities are described. Results are presented from tests of the photoacoustic cell in experiments to detect light absorption by ammonia in nitrogen flows using a single-mode diode laser with a wavelength of ~1.53 μm. The amplitude-frequency characteristics of the photoacoustic absorption response with and without ammonia are analyzed. The operation of the cell under conditions of resonance with the second longitudinal acoustic mode of the inner cavity of the cell (resonant frequency 4.38 kHz, Q-factor 13.9) is analyzed. The measured background signal level from the cell windows corresponds to an absorption coefficient of ~2.8·10–7 cm–1. The microphone-noise limited minimum detectable absorption is ~1.44·10–9 cm–1·W·Hz1/2.