Showing papers on "Photoacoustic spectroscopy published in 2021"
TL;DR: In this article, an overview on QEPAS technique, highlighting merits and drawbacks, aims at providing ready-to-use guidelines for multi-gas detection in a wide range of applications and operating conditions.
57 citations
TL;DR: In this paper, a multi-pass laser beam pattern through the prong spacing of a quartz tuning fork (QTF) is obtained by means of two right-angle prisms.
Abstract: A multi-pass quartz-enhanced photoacoustic spectroscopy (MP-QEPAS)-based trace gas sensor is reported. In MP-QEPAS, a multi-pass laser beam pattern through the prong spacing of a quartz tuning fork (QTF) is obtained by means of two right-angle prisms. A large QTF with the prong length of 17 mm and prong spacing of 0.8 mm was employed to increase the passage of multi-pass time and ease the alignment of the beam reflection pattern through the QTF. This multi-pass configuration allows the laser beam to pass through the QTF prong spacing six times. Water vapor (H2O) was chosen as target gas to investigate the performance of the MP-QEPAS sensor. Compared to a conventional QEPAS measurement, the MP-QEPAS technique provided an enhancement of signal level of ∼3.2 times.
50 citations
TL;DR: In this article, the authors demonstrated that quartzenhanced photoacoustic spectroscopy (QEPAS) is an efficient tool to measure the vibrational relaxation rate of gas species, employing quartz tuning forks (QTFs) as sound detectors.
50 citations
TL;DR: The optimized T-type longitudinal resonant PA cell features of high PA cell constant, fast response time and simple manufacturing process are presented.
49 citations
TL;DR: In this paper, a trace gas detection technique of quartzenhanced photoacoustic-photothermal spectroscopy (QEPA-PTS) is demonstrated, where water vapor (H2O) with a volume concentration of 1.01% was selected as the analyte gas to investigate the sensor performance.
Abstract: A trace gas detection technique of quartz-enhanced photoacoustic-photothermal spectroscopy (QEPA-PTS) is demonstrated. Different from quartz-enhanced photoacoustic spectroscopy (QEPAS) or quartz-enhanced photothermal spectroscopy (QEPTS), which detected only one single kind of signal, QEPA-PTS was realized by adding the photoacoustic and photothermal signals generated from two quartz tuning forks (QTFs), respectively. Water vapor (H2O) with a volume concentration of 1.01% was selected as the analyte gas to investigate the QEPA-PTS sensor performance. Compared to QEPAS and QEPTS, an enhanced signal level was achieved for this QEPA-PTS system. Further improvement of such a technique was proposed.
49 citations
TL;DR: In this paper, a single-quartzenhanced dual spectroscopy (S-QEDS)-based trace gas sensor is reported for the first time, to the best of our knowledge.
Abstract: A single-quartz-enhanced dual spectroscopy (S-QEDS)-based trace gas sensor is reported for the first time, to the best of our knowledge. In S-QEDS, a quartz tuning fork (QTF) was utilized to detect the photoacoustic and photothermal signals simultaneously and added the two signals together. The S-QEDS technique not only improved the detection performance but also avoided the issue of resonant frequency mismatching of QTFs for the multi-QTFs-based sensor systems. Water vapor (${\rm H}_2{\rm O}$) was selected as the target gas to investigate the S-QEDS sensor performance. The photoacoustic, photothermal, and composited signals were measured, respectively, under the same conditions. The experimental results verified the ideal adding of the photoacoustic and photothermal signals by using a single QTF in this S-QEDS sensor system.
46 citations
TL;DR: In this paper, a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for hydrogen sulfide (H2S) detection, exploiting a liquid-nitrogen-cooled THz quantum cascade laser (QCL) operating in pulsed mode, was presented.
42 citations
TL;DR: In this article, photoacoustic spectroscopy (PAS) is used for gas sensing, which usually uses a capacitive microphone as a signal detector, but the electric nature of the microphone limits its performance.
Abstract: Photoacoustic spectroscopy (PAS) is an ultrasensitive method for gas sensing, which usually using a capacitive microphone as a signal detector. However, the electric nature of the microphone limits...
40 citations
37 citations
TL;DR: The broadband differential photoacoustic trace gas detection was shown to be an effective approach for traceGas detection due to the suppression of background noise accomplished by the optimized wavelet domain denoising algorithm.
34 citations
TL;DR: A ppb-level H2S and CO photoac acoustic spectroscopy (PAS) gas sensor was developed by using a two-stage commercial optical fiber amplifier with a full output power of 10 W and a dual-resonator structural photoacoustic cell was theoretically simulated and designed with a finite element analysis.
Abstract: A ppb-level H2S and CO photoacoustic spectroscopy (PAS) gas sensor was developed by using a two-stage commercial optical fiber amplifier with a full output power of 10 W. Two near-infrared diode lasers with the central wavenumbers of 6320.6 cm−1 and 6377.4 cm−1 were employed as the excitation laser source. A time-division multiplexing method was used to simultaneously detect CO and H2S with an optical switch. A dual-resonator structural photoacoustic cell (PAC) was theoretically simulated and designed with a finite element analysis. A µV level background noise was achieved with the differential and symmetrical PAC. The performance of the multi-component sensor was evaluated after the optimization of frequency, pressure and modulation depth. The minimum detection limits of 31.7 ppb and 342.7 ppb were obtained for H2S and CO at atmospheric pressure.
TL;DR: In this paper, a radial cavity with (0,0,1) resonance mode was coupled with the quartz tuning fork (QTF) to greatly enhance the QEPAS signal and facilitate the optical alignment.
Abstract: Radial-cavity quartz-enhanced photoacoustic spectroscopy (RC-QEPAS) was proposed for trace gas analysis. A radial cavity with (0,0,1) resonance mode was coupled with the quartz tuning fork (QTF) to greatly enhance the QEPAS signal and facilitate the optical alignment. The coupled resonance enhancement effects of the radial cavity and QTF were analyzed theoretically and researched experimentally. With an optimized radial cavity, the detection sensitivity of QEPAS was enhanced by >1 order of magnitude. The RC-QEPAS makes the acoustic detection module more compact and optical alignment comparable with a bare QFT, benefiting the usage of light sources with poor beam quality.
20 Apr 2021
TL;DR: In this article, the authors exploit light-gas-acoustic interaction in a gas-filled anti-resonant hollow-core-fiber (AR-HCF) to demonstrate photoacoustic Brillouin spectroscopy (PABS).
Abstract: Photoacoustic spectroscopy, a powerful tool for gas analysis, typically uses bulky gas cells and discrete microphones. Here we exploit light-gas-acoustic interaction in a gas-filled anti-resonant hollow-core-fiber (AR-HCF) to demonstrate photoacoustic Brillouin spectroscopy (PABS). Pump absorption of gas molecules excites the acoustic resonances of the fiber, which modulates the phase of a probe beam propagating in the fiber. Detection of the phase modulation enables spectroscopic characterization of gas species and concentration as well as the fiber microstructure. Studying the acoustic resonances allows us to characterize the longitudinal inhomogeneity of the fiber microstructure. By tuning the pump modulation frequency to a wine-glass-like capillary mode of a 30-cm-long AR-HCF and the pump wavelength across a gas absorption line, we demonstrate detection of acetylene at the parts-per-billion level. PABS has great potential for high sensitivity gas sensing and non-invasive fiber characterization.
TL;DR: In this paper, a comparison between two optical detection techniques, one based on a Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) detection module, where a quartz tuning fork is acoustically coupled with a pair of millimeter-sized resonator tubes; and the other based on Photothermal Spectroscopic (PTS) module where a Fabry-Perot interferometer acts as transducer to probe refractive index variations.
TL;DR: In this paper, an all-optical high-sensitivity resonant photoacoustic (PA) sensor is presented to realize remote, long-distance and space-limited trace gas detection.
Abstract: This paper presents an all-optical high-sensitivity resonant photoacoustic (PA) sensor to realize remote, long-distance and space-limited trace gas detection. The sensor is an integration of a T-type resonant PA cell and a particular cantilever-based fiber-optic acoustic sensor. The finite element simulations about the cantilever vibration mode and the PA field distributions are carried out based on COMSOL. The all-optical high-sensitivity resonant PA sensor, together with a high-speed spectrometer and a DFB laser source, makes up of a photoacoustic spectroscopy (PAS) system which is employed for CH4 detection. The measured sensitivity is 0.6 pm/ppm in the case of 1000 s average time, and the minimum detection limit (MDL) reaches 15.9 parts per billion (ppb). The detective light source and the excitation light source are all transmitted by optical fibers, therefore remote and long-distance measurement of trace gas can be realized. Furthermore, the excitation light source and the acoustic sensor are designed at the same side of the PA cell, the sensor may be used for space-limited trace gas detection.
TL;DR: In this paper, a high-sensitivity N2O photoacoustic sensor using a 4.53 μm quantum cascade laser was developed, which achieved high performance with a minimum detection limit of 28 ppbv in 1 s and a measurement precision of 34ppbv, respectively.
TL;DR: In this article, an integrated spherical photoacoustic cell (SPAC) for trace methane (CH4) gas detection is presented, which can be used for remote and long-distance trace gas detection.
Abstract: This paper presents an integrated spherical photoacoustic cell (SPAC) for trace methane (CH4) gas detection. Theoretical analysis and analogue simulations are carried out to analyze the acoustic field distribution of the SPAC at resonant and non-resonant modes. The finite element simulation results based on COMSOL show that the first-order radial resonant frequency and second-order angular resonant frequency are 24,540 Hz and 18,250 Hz, respectively, which show good agreements with the formula analysis results. The integrated SPAC, together with a high-speed spectrometer and a distributed feedback (DFB) laser source, makes up a photoacoustic (PA) spectroscopy (PAS) system, which is employed for CH4 detection. The minimum detection limit (MDL) is measured to be 126.9 parts per billion (ppb) at an average time of 1000 s. The proposed SPAC has an integrated, miniaturized and all-optical structure, which can be used for remote and long-distance trace gas detection.
TL;DR: In this paper, a single-line spot pattern multi-pass cell (MPC) is designed to make a laser beam pass through a quartz tuning fork (QTF) 60 times, thus producing 60 sound sources between the two QTF prongs.
Abstract: Multiple-sound-source-excitation quartz-enhanced photoacoustic spectroscopy (MSSE-QEPAS) based on a single-line spot pattern multi-pass cell (MPC) is reported for trace gas detection. The single-line spot pattern MPC is designed to make a laser beam pass through a quartz tuning fork (QTF) 60 times, thus producing 60 sound sources between the two QTF prongs. These sound sources excite the QTF operating at fundamental resonance mode in phase, resulting in a signal gain factor of ∼20. A theoretical mode based on convolution method is proposed to explain the working mechanism of MSSE-QEPAS.
TL;DR: In this article, a new type of ellipsoid photo-acoustic cell was designed to enhance the photoacoustic effect for the first time, which was used to detect the concentration of acetylene.
TL;DR: In this paper, a method based on photoacoustic spectroscopy that can simultaneously measure the aerosol absorption characteristics of three wavelengths (404, 637 and 805 nm) is proposed.
Abstract: Aerosol optical absorption measurements are important for the prediction of climate change, as aerosols directly disturb Earth's radiation balance by absorbing or scattering solar radiation. Although photoacoustic spectroscopy is commonly recognized as one of the best candidates to measure the absorption of aerosols, multi-wavelength measurements of aerosols optical absorption remain challenging. Here, a method based on photoacoustic spectroscopy that can simultaneously measure the aerosol absorption characteristics of three wavelengths (404, 637 and 805 nm) is proposed. In the three-wavelength photoacoustic spectrometer (TW-PAS), a photoacoustic cell with three acoustic resonators operating at different resonant frequencies was designed for offering multi-laser (multi-wavelength) operation simultaneously, and only one microphone was used to measure the acoustic signals of all resonators. The performance of TW-PAS was demonstrated and evaluated by measuring and analyzing the wavelength-dependent absorption coefficients of carbonaceous aerosols, which shows good agreement with previously reported results. The developed TW-PAS exhibits high potential for classifying and quantifying different types of light-absorbing aerosols by analyzing its absorption wavelength dependence characteristics.
TL;DR: In this article, a ppb-level photoacoustic sensor for C2H2 was developed for transformer insulation status detection, and the results indicate that the detection limit of proposed system can reach ~3.4 ppb.
TL;DR: In this article, the authors compared diffuse reflectance spectroelectrochemistry (SE-DRS) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) to obtain the density of electronic states (DOS) in the vicinity of the conduction band bottom.
Abstract: The diffuse reflectance spectroelectrochemistry (SE-DRS) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) provide unique, complementary information on the density of electronic states (DOS) in the vicinity of the conduction band bottom. The measurements are performed under quite different conditions, representing the solid/liquid and solid/gas interfaces in SE-DRS and RDB-PAS, respectively. DOS profiles obtained from both types of measurements can be considered as unique "fingerprints" of the tested materials. The analysis of DOS profiles recorded for 16 different TiO2 samples confirms that both methods similarly describe the shapes of DOS profiles around the conduction band edges. The states characterized by energy higher than VBT (valence-band top) + Eg can be considered as electronic states within the conduction band. Recognition of the potential of the conduction band bottom allows one to classify the electronic states as deep or shallow electron traps or conduction band states, which play different roles in photocatalysis. The comparative analysis shows that both methods provide very useful information which can be used in understanding and predicting the photo(electro)catalytic reactivity of semiconductors.
TL;DR: In this article, the authors reported on the sub-parts-per-billion-level radiocarbon dioxide detection using cantilever-enhanced photoacoustic spectroscopy.
Abstract: In this Letter, we report on the sub-parts-per-billion-level radiocarbon dioxide detection using cantilever-enhanced photoacoustic spectroscopy. The 14C/C ratio of samples is measured by targeting a 14CO2 absorption line with minimal interference from other CO2 isotopes. Using a quantum cascade laser as a light source allows for a compact experimental setup. In addition, measurements of sample gases with 14CO2 concentrations as low as 100 parts-per-trillion (ppt) are presented. The Allan deviation demonstrates a noise equivalent concentration of 30 ppt at an averaging time of 9 min. The achieved sensitivity validates this method as a suitable alternative to more complex optical detection methods for radiocarbon dioxide detection used so far, and it can be envisioned for future in situ radiocarbon detection.
TL;DR: An analytic model to optimize the geometry of a cantilever used as a capacitive transducer in photoacoustic spectroscopy using computational methods implemented in a Python programming environment is presented.
Abstract: We propose a new concept of photoacoustic gas sensing based on capacitive transduction which allows full integration while conserving the required characteristics of the sensor. For the sensor’s performance optimization, trial and error method is not feasible due to economic and time constrains. Therefore, we focus on a theoretical optimization of the sensor reinforced by computational methods implemented in a Python programming environment. We present an analytic model to optimize the geometry of a cantilever used as a capacitive transducer in photoacoustic spectroscopy. We describe all the physical parameters which have to be considered for this optimization (photoacoustic force, damping, mechanical susceptibility, capacitive transduction, etc.). These parameters are characterized by opposite trends. They are studied and compared to obtain geometric values for which the signal output and signal-to-noise ratio are maximized.
TL;DR: In this paper, a gas detection system based on one cantilever beam sensor and a single-pass photoacoustic (PA) spectroscopy cell was proposed, where infrared light beams were coupled by the coarse wavelength division multiplexer (CWDM) and fiber coupler, the vibration of the cantilevers beam was measured by the vibration meter, and the gas detection experiment was carried out.
Abstract: Gas detection based on photoacoustic (PA) spectroscopy has attracted extensive attention due to high sensitivity and portability. Herein, to achieve the simultaneously detection of the transformer oil carbide gases, C2H2 and CO, a gas-detection system based on one cantilever beam sensor and single-pass PA cell was proposed. The infrared light beams were coupled by the coarse wavelength division multiplexer (CWDM) and fiber coupler, the vibration of the cantilever beam was measured by the vibration meter, and the gas detection experiment was carried out. The results showed that cantilever could distinguish multiple kinds of acoustic waves, in the frequency domain, the simultaneous detection of C2H2 and CO can be realized by extracting the fast Fourier transform (FFT) values at 20 and 55 Hz. The system exhibits a good repeatability, and a linear relationship between the pure PA signals and gas concentration was confirmed with the correlation coefficient greater than 0.9. In addition, the pure PA signals also show linear trend with the coupling ratio. The minimum detection limit and resolution of C2H2 are 0.27 and 0.12 per part million (ppm), respectively, when the CWDM is used to couple the light beams, whereas they are 23.42 and 14.94 ppm of CO. Especially, it was found that the PA signals have good superposition whether the modulation frequencies of the external lasers are same or not. This article provides an idea for simultaneous detection of multicomponent in gas mixture.
TL;DR: An optical system for gaseous chloroform (CHCl3) detection based on wavelength modulation photoacoustic spectroscopy (WMPAS) was proposed for the first time by using a distributed feedback (DFB) laser with a center wavelength of 1683 nm.
Abstract: An optical system for gaseous chloroform (CHCl3) detection based on wavelength modulation photoacoustic spectroscopy (WMPAS) is proposed for the first time by using a distributed feedback (DFB) laser with a center wavelength of 1683 nm where chloroform has strong and complex absorption peaks. The WMPAS sensor developed possesses the advantages of having a simple structure, high-sensitivity, and direct measurement. A resonant cavity made of stainless steel with a resonant frequency of 6390 Hz was utilized, and eight microphones were located at the middle of the resonator at uniform intervals to collect the sound signal. All of the devices were integrated into an instrument box for practical applications. The performance of the WMPAS sensor was experimentally demonstrated with the measurement of different concentrations of chloroform from 63 to 625 ppm. A linear coefficient R2 of 0.999 and a detection sensitivity of 0.28 ppm with a time period of 20 s were achieved at room temperature (around 20 °C) and atmosphere pressure. Long-time continuous monitoring for a fixed concentration of chloroform gas was carried out to demonstrate the excellent stability of the system. The performance of the system shows great practical value for the detection of chloroform gas in industrial applications.