Highly sensitive13C16O2-laser photoacoustic detection of ammonia, phosphine and arsine in air

Highly sensitive acetylene detection based on multi-pass retro-reflection-cavity-enhanced photoacoustic spectroscopy and a fiber amplified diode laser

In this paper, a multi-pass retro-reflection-cavity-enhanced photoacoustic spectroscopy (PAS) based gas sensor is reported for the first time. The multi-pass retro-reflection-cavity consisted of two right-angle prisms and was designed to reflect the laser beam to pass through the photoacoustic (PA) cell four times, which improved the acetylene (C₂H₂)-PAS sensor signal level significantly. The optical power of a near-infrared distributed feedback (DFB) diode laser emitting a continuous wave (CW) was amplified to 1000 mW with an erbium-doped fiber amplifier. The background noise was reduced with wavelength modulation spectroscopy (WMS) and 2nd harmonic demodulation techniques. The linear optical power and concentration response of such a PAS sensor were investigated, and the experimental results showed excellent characteristics. When the integration the time of the sensor system was set to 1 s, the minimum detection limit (MDL) for C₂H₂ detection was 8.17 ppb, which corresponds to a normalized noise equivalent absorption coefficient (NNEA) of 1.84 × 10^-8 cm^-1W/√Hz. The long-term stability of such a multi-pass retro-reflection-cavity-enhanced PAS based C₂H₂ sensor was evaluated by an Allan deviation analysis. It was demonstrated that the multi-pass retro-reflection-cavity-enhanced PAS sensor had an excellent stability. An MDL of 600 ppt was achieved when the integration time was set to ~1000 s. It was verified that the method of multi-pass retro-reflection-cavity-enhanced PAS with an amplified laser source improved the sensor performance significantly. If an appropriate cavity design with increasing reflection times is used, the MDL of such a PAS-based sensor can be further improved.

A variationally computed room temperature line list for AsH3

Calculations are reported on the rotation–vibration energy levels of the arsine molecule with associated transition intensities.

Intracavity photoacoustic sensing of water vapor with a continuously tunable external-cavity quantum-cascade laser operating near 5.5 μm

A gas sensor integrating a pulsed external-cavity quantum-cascade laser and a photoacoustic (PA) cell placed inside the laser cavity is described. The laser design allows a continuously tunable and mode-hop-free operation with an estimated instrument-limited linewidth of 0.063  cm^-1 in Littrow or Littman-Metcalf cavity configurations. Due to higher intracavity power levels, the PA signal for the cell located within the laser cavity is 80-320 times stronger than the signal for the same cell placed outside the cavity. The sensor shows a good capability to identify individual absorption lines of isotopic H₂O16, H₂O8, and H₂O17 species within a narrow spectral interval from 1814 to 1821  cm^-1 at natural isotope abundances.