Broadband cantilever-enhanced photoacoustic spectroscopy in the mid-IR using a supercontinuum

Abstract

We demonstrate cantilever-enhanced photoacoustic spectroscopy in the mid-infrared using a supercontinuum source. The approach is broadband, compact, and allows for higher photoacoustic signal intensity and enhanced signal-to-noise ratio as compared to systems employing conventional back body radiation sources. Using this technique, we perform spectroscopic measurements of the full ro-vibrational band structure of water vapor at 1900 nm and methane at 3300 nm with relative signal enhancement factors of 70 and 19, respectively, when compared to measurements that use a black body radiation source. Our results offer novel perspective for photoacoustic detection opening the door to compact and sensitive broadband analyzers in the mid-infrared spectral region.

Optical frequency comb photoacoustic spectroscopy

“…In this first demonstration, we measured high resolution PA spectra of the fundamental C-H stretch band of methane, CH 4 , in nitrogen, N 2 , at different pressures, in good agreement with simulations based on the HITRAN database. 24 Spectral resolution up to 400 MHz, limited by the pressure broadening and 75 times better than the best reported using a SC source (30 GHz), 19 has been accomplished. These capabilities open up for new insights for high resolution multicomponent trace gas analysis in small sample volumes.…”

“…As shown in Table 2, the LOD is comparable for the three methods, while the resolution of OFC-PAS is more than two orders of magnitude better. Moreover, considering the lower power spectral density and the higher resolution of OFC-PAS compared to SC-PAS, 19 the attainable LOD of OFC-PAS becomes about a factor of five better than that of SC-PAS.…”

“…12,13,15 The implementation of cantilever-enhanced detectors significantly increased the detection sensitivity and FT-IR-PAS setups with detection limits of methane of 1.5 ppm (3s, 100 s, spectral resolution 4 cm À1 ), 18 and 3 ppm (2s, 168 s, spectral resolution 8 cm À1 ) 15 have been reported. In a very recent demonstration, Mikkonen et al 19 used a supercontinuum (SC) light source for broadband cantilever-enhanced PA detection and reported a limit of detection for methane of 1.4 ppm (3s, 50 s, spectral resolution 4 cm À1 ). Although the brightness of SC sources exceeds that of thermal emitters by orders of magnitude, the noise level is also increased, which is the reason for the relatively small improvement of the detection limit.…”

Cavity-enhanced cantilever-enhanced photo-acoustic spectroscopy

“…CEPAS is suitable for broadband spectroscopy, as it does not require operation in an acoustic resonance of the cell nor the cantilever to reach high sensitivity. 9,10 Moreover, CEPAS has demonstrated a large linear dynamic range of at least six orders of magnitude, and its noise performance has reached the ultimate limit of the Brownian noise from the thermal movement of gas molecules. 11 CEPAS analysers with parts-per-trillion ( ppt, volume mixing ratio) level sensitivity have been demonstrated using high-power lasers in several applications.…”

Photo-acoustic dual-frequency comb spectroscopy

“…The achievable resolution is determined by the scan range of the interferometer, which can reach several meters for high resolution instruments. In addition to temporally incoherent light sources, such as supercontinua 16 , coherent broadband spectra (unresolved optical frequency combs) have been used to improve the overall performance 17,18 . Combining frequency combs with scanning Fourier-transform spectrometers also permits using techniques for sub-nominal resolution 19 .…”