Ultrasensitive gas detection by quartz-enhanced photoacoustic spectroscopy in the fundamental molecular absorption bands region

Simultaneous atmospheric nitrous oxide, methane and water vapor detection with a single continuous wave quantum cascade laser

“…Therefore, QCL-based gas sensor systems [17] are widely used for high sensitivity and selectivity trace gas detection in a variety of applications including environmental monitoring [18][19][20] and medical diagnostics [21,22]. A CW DFB-QCL (Corning Inc., New York) with a wavelength of ~7.73 µm was used as an excitation source to target the absorption lines near 1297 cm −1 for simultaneous multiple species gas detection.…”

Compact QEPAS sensor for trace methane and ammonia detection in impure hydrogen

“…Recent studies reported that the optimum length of each mR tube is between λ s /4 and λ s /2 where λ s is the wavelength of sound [3,5]. [11][12][13][14][15][16]. QEPAS has also been demonstrated with larger molecules with broad, unresolved absorption spectra, such as ethanol, acetone and freon [17].…”

CO2 Laser Photoacoustic Spectroscopy: II. Instrumentation and Applications

“…Our CO 2 laser photoacoustic system with a α min value of 2.7x10 -8 cm -1 should provide interference-free minimum detectable concentrations between 0.9 ppbV and 270 ppbV for vapors with usual absorption coefficients of 30-0.1 cm -1 atm -1 . Cell sensitivity for 1 ppbV of C 2 H 4 at 1 W of unchopped laser power n , V ppb (µV at 1 ppbV) 3.0 a This quality factor value corresponds to a full bandwidth at the 0.707 amplitude points of Δf = f0/Q ≅ 35 Hz b The cell responsivity is the signal per unit power per unit absorption coefficient; in our case, the signal per unit power is 11.6 mV/4.0 W = 2.9x10 -3 V/W (rms value) or 8.2x10 -3 V/W (peak-to-peak value) for VR (several authors, e.g., (Harren et al, 1990a) used the rms value of the voltage instead of its peak-to-peak value, resulting in a limiting sensitivity of the cell and of the system and the limiting measurable concentration of ethylene lower by a factor of 2.84; other authors, e.g., (Kosterev et al, 2005), used a parameter named "sensitivity to absorption", V , P L is the laser excitation power, and Δf is the detection bandwidth). g The limiting sensitivity of the system or the microphone noise-limited minimum detectable absorption coefficient (the equivalent bulk absorption coefficient in the gas) is S sys = S cell /P L (the minimum detectable absorption strength is defined as the strength that gives a SNR at the transducer output equal to one).…”