Portable broadband photoacoustic spectroscopy for trace gas detection by quantum cascade laser arrays

Abstract

We report a portable broadband photoacoustic spectroscopic system for trace gas detection using distributed feedback quantum cascade laser arrays. By sequentially firing 128 lasers, our system acquires a photoacoustic spectrum covering 565 c m − 1 ( 935 − 1500 c m − 1 ) with a normalized-noise-equivalent-absorption coefficient of 2.5 × 10 − 9 c m − 1 W H z − 1 / 2 . The firing sequence that determines when and which laser to activate is programmable, which enables frequency-multiplexing excitation. For demonstration, 12 lasers are modulated simultaneously at distinct frequencies, and a photoacoustic spectrum is acquired within 13 ms. The compactness ( 28 c m × 17 c m × 13 c m , 3.5 kg) and low power consumption enable convenient installation for on-site monitoring.

Fluorescence-Detected Mid-Infrared Photothermal Microscopy

“…The average power of the green laser was around 0.2 mW on the sample plane for rhodamine-6G (R6G) associated samples and 30 mW for samples associated with Nile red as the fluorescent reporter. The monolithic QCL included 32 independently addressable wavelength channels in the range of wavenumbers from 1190 to 1330 cm –1 . In typical operation, the QCL array was operated in a burst mode, in which a rapid series of 300 ns laser pulses was sequentially activated firing every 8 μs for “on” cycles ranging from 20 to 250 μs, followed by quiescent “off” periods of equal duration, with an average power of ≤0.8 mW on the sample plane.…”

“…The monolithic QCL included 32 independently addressable wavelength channels in the range of wavenumbers from 1190 to 1330 cm −1 . 30 In typical operation, the QCL array was operated in a burst mode, in which a rapid series of 300 ns laser pulses was sequentially activated firing every 8 μs for "on" cycles ranging from 20 to 250 μs, followed by quiescent "off" periods of equal duration, with an average power of ≤0.8 mW on the sample plane. Timing details are described in greater detail in the Supporting Information.…”

Small-volume highly-sensitive all-optical gas sensor using non-resonant photoacoustic spectroscopy with dual silicon cantilever optical microphones

“…The mid-infrared (MIR) region lasers may be used, with over two orders of magnitude stronger gas absorption than the visible and near-infrared (NIR) region [17] . With the development of laser technology, various kinds of higher power MIR lasers are applied to increase photoacoustic signal, such as quantum cascade lasers [18] , [19] , interband cascade lasers [20] , [21] and optical parametric oscillators [22] . However, the high cost and maturity of MIR lasers limit their applications.…”

Modeling of a cylindrical resonant photoacoustic cell for high sensitive gas detection

“…Vafaie et al 25 used finite element method to solve the coupled photoacoustic equation in gas environment, and analyzed the influence of various effective parameters such as frequency response, quality factor, sound pressure and heat. Liao et al 26 reported a portable broadband PAS detection system for trace gas detection using distributed feedback quantum cascade laser arrays with a noise‐cancel‐absorption coefficient of . Dong et al 27 developed a sensitive photoacoustic sensor system for the detection of ppb‐level sulfur dioxide (SO 2 ) using a continuous‐wave room‐temperature high‐power quantum cascade laser (QCL) with an external diffraction grating cavity structure.…”