Sensitive Spectroscopy of Acetone Using a Widely Tunable External-Cavity Quantum Cascade Laser

Abstract

We employed a single-mode, widely tunable (~300 cm−1) external-cavity quantum cascade laser operating around 8 µm for broadband direct absorption spectroscopy and wavelength modulation spectroscopy where a modulation frequency of 50 kHz was employed with high modulation amplitudes of up to 10 GHz. Using a compact multipass cell, we measured the entire molecular absorption band of acetone at ~7.4 µm with a spectral resolution of ~1 cm−1. In addition, to demonstrate the high modulation dynamic range of the laser, we performed direct absorption (DAS) and second harmonic wavelength modulation spectroscopy (WMS-2f) of the Q-branch peak of acetone molecular absorption band (HWHM ~10 GHz) near 1365 cm−1. With WMS-2f, a minimum detection limit of 15 ppbv in less than 10 s is achieved, which yields a noise equivalent absorption sensitivity of 1.9 × 10−8 cm−1 Hz−1/2.

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

“…Now, many commercial providers offer cw-and RT-operated QCLs in different configurations ranging from Fabry-Perot devices, to DFB resonators, to external cavities-based (EC-) QCLs, as well as high-power devices (with watts) in the infrared to terahertz spectral region. QCLs are attractive for infrared countermeasure, metrology, high-resolution spectroscopy, and chemical sensing applications [7,[47][48][49][50][51][52][53].…”

Experimental-based comparison between off-axis integrated cavity output spectroscopy and multipass-assisted wavelength modulation spectroscopy at 77 µm

“…For our experiments a homemade EC-QC laser was developed, as described elsewhere in detail [21,39]. The EC-QC laser supports single mode operation and wide spectral tunability for broadband emission.…”

“…1(b)). Although the QCL chip is fabricated based on the same design as the one that we used in [39], the output power is improved by a factor two and the threshold current is reduced by ∼50%. These enhancements are attributed to an optimized alignment within the external cavity.…”

Экспериментальная установка на базе перестраиваемого в диапазоне волн 5.3-12.8 μm квантово-каскадного лазера для спектрального анализа выдыхаемого человеком воздуха

“…Так, например, лазер с длиной волны 8.2 µm используется для исследования линий ацетона и метана [39], 5.2 µm -линии NO [40], 10.3 µm -аммиака [41]. В работе [42] используется лазер с перестройкой порядка 300 cm −1 для спектрального анализа нескольких линий поглощения ацетона.…”