Resonant Photoacoustic Spectroscopy Research Articles

Online Detection of Hydrogen Fluoride under Corona Discharge in Gas-Insulated Switchgear Based on Photoacoustic Spectroscopy.

Internal discharge and overheating faults in sulfur hexafluoride (SF6) gas-insulated electrical equipment will generate a series of characteristic gas products. Hydrogen fluoride (HF) is one of the main decomposition gases under discharge failure. Because of its extremely corrosive nature, it can react with other materials in gas-insulated switchgear (GIS), resulting in a short existence time, so it needs to be detected online. Resonant gas photoacoustic spectroscopy has the advantage of high sensitivity, fast response, and no sample gas consumption, and can be used for the online detection of flowing gas. In this paper, a simulated GIS corona discharge experimental platform was built, and the HF generated in the discharge was detected online by gas photoacoustic spectroscopy. The absorption peak of HF molecule near 1312.59 nm was selected as the absorption spectral line, and a resonant photoacoustic cell was designed. To improve the detection sensitivity of HF, wavelength modulation and second-harmonic detection technology were used. The online monitoring of HF in the simulated GIS corona discharge fault was successfully realized. The experimental results show that the sensitivity of the designed photoacoustic spectroscopy detection system for HF is 0.445 μV/(μL/L), and the limit of detection (LOD) is 0.611 μL/L.

Quartz-enhanced multiheterodyne resonant photoacoustic spectroscopy

The extension of dual-comb spectroscopy (DCS) to all wavelengths of light along with its ability to provide ultra-large dynamic range and ultra-high spectral resolution, renders it extremely useful for a diverse array of applications in physics, chemistry, atmospheric science, space science, as well as medical applications. In this work, we report on an innovative technique of quartz-enhanced multiheterodyne resonant photoacoustic spectroscopy (QEMR-PAS), in which the beat frequency response from a dual comb is frequency down-converted into the audio frequency domain. In this way, gas molecules act as an optical-acoustic converter through the photoacoustic effect, generating heterodyne sound waves. Unlike conventional DCS, where the light wave is detected by a wavelength-dependent photoreceiver, QEMR-PAS employs a quartz tuning fork (QTF) as a high-Q sound transducer and works in conjunction with a phase-sensitive detector to extract the resonant sound component from the multiple heterodyne acoustic tones, resulting in a straightforward and low-cost hardware configuration. This novel QEMR-PAS technique enables wavelength-independent DCS detection for gas sensing, providing an unprecedented dynamic range of 63 dB, a remarkable spectral resolution of 43 MHz (or ~0.3 pm), and a prominent noise equivalent absorption of 5.99 × 10-6 cm-1·Hz-1/2.

Parts-per-billion-level detection of hydrogen sulfide based on doubly resonant photoacoustic spectroscopy with line-locking

We report on the development of a highly sensitive hydrogen sulfide (H2S) gas sensor exploiting the doubly resonant photoacoustic spectroscopy technique and using a near-infrared laser emitting at 1578.128 nm. By targeting the R(4) transition of H2S, we achieved a minimum detection limit of 10 part per billion in concentration and a normalized noise equivalent absorption coefficient of 8.9 × 10−12 W cm−1 Hz−1/2. A laser-cavity-molecule locking strategy is proposed to enhance the sensor stability for fast measurement when dealing with external disturbances. A comparison among the state-of-the-art H2S sensors using various spectroscopic techniques confirmed the record sensitivity achieved in this work.

A sensor based on high-sensitivity multi-pass resonant photoacoustic spectroscopy for detection of hydrogen sulfide

A high-sensitive tunable diode laser sensor based on photoacoustic spectroscopy and multi-pass absorption spectroscopy is developed for hydrogen sulfide (H2S) detection using a target absorption line at 6287.005 cm−1. Two spherical concave mirrors are utilized as the reflectors to make the laser beam pass through the photoacoustic cell for 24 times. The wavelength modulation spectroscopy technique with second harmonic detection (WMS-2f) method is employed to reduce external interference and increase the detection sensitivity. With the enhancement of the effective laser power in the multi-pass PA cell, the photoacoustic 2f signal of the target H2S absorption line has a ∼ 8 times improvement compared to the sensor system without multi-pass cell. Based on the results of Allan variance analysis, the minimum detection concentration of the system could reach 0.68 ppm with a 10-s average time and it can be further lowered down to ∼ 0.1 ppm when a 1-minute averaging time is used. The linear responsivity of the multi-pass PA spectroscopy sensor is estimated to be ∼ 0.00112 mV/ppm by linear fitting for a continuous flow gas measurement results. The excellent performance validates the potential of the sensor for field application.

Miniaturized anti-interference cantilever-enhanced fiber-optic photoacoustic methane sensor

To realize all-optical passive detection of CH 4 in narrow spaces and harsh environments, a compact cantilever-enhanced fiber-optic photoacoustic sensor (CEFPS) resistant to electromagnetic and ambient noise interference is proposed. Through theoretical analysis and finite element simulation, a miniaturized photoacoustic cell (PAC) with diffusion holes has been designed and fabricated. The diffusion holes are used for the circulation of the gas to be measured and attenuate the external noise coupled into the PAC. The concentration information of CH 4 is obtained by demodulating the vibration amplitude of the built-in cantilever generated by the photoacoustic pressure. The design of the built-in cantilever structure avoids the possibility of mechanical damage and reduces the interference of external noise in the detection of photoacoustic signals. The experimental results and the Allan-Werle deviation analysis of the CH 4 signal show that the minimum detection limit (MDL) is 0.32 ppm with an integration time of 60 s. The normalized noise equivalent absorption (NNEA) coefficient is calculated as 2.44 × 10 −8 cm −1 W/Hz 1/2 . The developed CEFPS achieves performance comparable to conventional resonant photoacoustic spectroscopy CH 4 detectors, although the volume is two orders of magnitude lower. • A miniaturized all-optical anti-interference cantilever-enhanced photoacoustic methane sensor is presented. • The cantilever acoustic-sensitive element and miniaturized photoacoustic cell (PAC) adopt a built-in design. • The direct effect of environmental noise interference, wind disturbance and mechanical damage on the cantilever is avoided. • The sensitivity of the sensor reaches the traditional resonant photoacoustic spectroscopy trace gas detection technology. • At the same time, the volume of the built-in miniaturized non-resonant PAC is reduced by about two orders of magnitude.

Sub‐ppb nitrogen dioxide detection based on resonant photoacoustic spectroscopy

AbstractA photoacoustic spectroscopy sensor for nitrogen dioxide (NO2) detection was presented based on a high‐power broadband blue diode laser emitting at 446 nm. An optical chopper was replaced by a transistor transistor logic modulation signal generated by the signal generator to reduce mechanical noise. The detection limit of NO2 sensor system reached to 46 ppt by the Allan variance analysis on the benefit of reflection‐enhanced. A continuous detection of NO2 in the atmosphere for 48 h was implemented in collaboration with an adaptive Kalman filter for lessening the noise in the measurement. The experimental results were highly consistent with the data of the China National Environmental Monitoring Center, demonstrating the accuracy and reliability of our NO2 sensor system. This work provides a promising method for NO2 and other atmospheric pollution gasses.

Acoustic resonance laser calorimetry for measurements of low optical absorption.

A novel method of acoustic resonance laser calorimetry (ARLC) for the determination of low optical absorption coefficients of crystals and glasses is introduced. It is based on measurements of the kinetics of the equivalent temperature of the sample irradiated by the pulse laser radiation. The equivalent temperature of the sample is directly obtained by measuring the frequency changes of its temperature-calibrated acoustic resonances excited by the laser radiation with a corresponding pulse repetition rate. In contrast to the conventional resonant photoacoustic spectroscopy, where the resonance is used for the enhancement of the registered signal, in ARLC, the laser-excited acoustic resonance of the sample acts as a high-sensitivity temperature probe for measurements of its heating kinetics. The ARLC approach was verified by measuring the optical absorption coefficient of the potassium dihydrogen phosphate crystal (α=4.2⋅10-2cm-1) at 1064 nm wavelength.

Mass Accommodation Coefficients of Water on Organics from Complementary Photoacoustic and Light Scattering Measurements on Laser-Trapped Droplets

The mass accommodation coefficient, $\alpha_M$, describes evaporation and condensation kinetics at the liquid-vapor interface. In spite of numerous experimental efforts, reliable values of $\alpha_M$ are still not available for many substances. Here, we present a novel experimental technique, photothermal single-particle spectroscopy (PSPS), that allows for a robust retrieval of mass accommodation coefficients from three simultaneous independent measurements. PSPS combines resonant photoacoustic absorption spectroscopy with modulated Mie scattering measurements on single particles. We study the mass transport of water on organic aerosol droplets that are optically trapped using counter-propagating tweezers. We find the mass accommodation coefficient of water on a pure model organic that is fully miscible with water to be 0.021 at 296K, and to decrease by more than an order of magnitude when the temperature increases to 309K. The experimentally observed temperature dependence of $\alpha_M$ shows an Arrheni...

Resonant Photoacoustic Spectroscopy of NO₂ with a UV-LED Based Sensor.

Nitrogen dioxide (NO2) is a poisonous trace gas that requires monitoring in urban areas. Accurate measurement in sub-ppm concentrations represents a wide application field for suitable economical sensors. We present a novel approach to measure NO2 with a photoacoustic sensor using a T-shaped resonance cell. An inexpensive UV-LED with a peak wavelength of 405 nm as radiation source as well as a commercial MEMS microphone for acoustic detection were used. In this work, a cell has been developed that enables a “non-contact” feedthrough of the divergent LED beam. Thus, unwanted background noise due to absorption on the inside walls is minimized. As part of the development, an acoustic simulation has been carried out to find the resonance frequencies and to visualize the resulting standing wave patterns in various geometries. The pressure amplitude was calculated for different shapes and sizes. A model iteratively optimized in this way forms the basis of a construction that was built for gas measurement by rapid prototyping methods. The real resonance frequencies were compared to the ones found in simulation. The limit of detection was determined in a nitrogen dioxide measurement to be 200 ppb (6 σ) for a cell made of aluminum.

Numerical study of geometrical effects on the performance of an H-type cylindrical resonant photoacoustic cell

We have numerically studied the geometrical effects on the performance of an H-type cylindrical resonant photoacoustic cell, composed of one resonator and two symmetrical buffer cylinders, by performing simulations on the generation of acoustic waves in the cell. Here, the acoustic response (pressure), resonance frequency and quality factor are calculated for the cell performance, while the lengths and diameters of both resonator and buffer cylinders are considered for the geometrical parameters or dimensions. Our calculation solves linearized forms of the continuity equation, Navier-Stokes equation, energy equation, and equation of state using a finite element method under an assumption that the heat addition due to the laser passage and thus the variations in the velocity, pressure and temperature fields inside the cell are small enough. First, we performed a statistical analysis using a design of experiment method to evaluate the relative impacts of the cell dimensions on the acoustic response. Subsequently, we performed a parametric study to quantify the cell performance with the dimensional variations. Our results, along with the response surface methodology, provide guidance for a systematic design optimization of the cell for the best acoustic response. The approach in this study may be applied to the design of various types of resonant photoacoustic spectroscopy devices.

Ultra-high sensitive fiber-optic Fabry-Perot cantilever enhanced resonant photoacoustic spectroscopy

A new scheme of fiber-optic cantilever enhanced resonant photoacoustic spectroscopy (CERPAS), combining high sensitive fiber-optic Fabry-Perot cantilever microphone with resonant photoacoustic spectroscopy, is presented for trace gas detection. A fiber-optic cantilever microphone with high sensitivity at the frequency near 1.4 kHz is designed to match with a first-order longitudinal resonant photoacoustic cell, whose resonant frequency is 1402 Hz. For sensitivity improvement, an erbium-doped fiber amplified near-infrared laser, with the central wavelength of 1532.83 nm and the maximum output power of 1 W, is used as the light source for acoustic excitation. The trace acetylene detection experiment demonstrates that, with the wavelength modulation spectrum and second-harmonic detection methods, the gas detection limit is achieved to be 80 ppt, which is at least one order of magnitude improvement compared with other photoacoustic acetylene sensors reported so far.

Fiber-amplifier-enhanced resonant photoacoustic sensor for sub-ppb level acetylene detection

A near-infrared fiber-amplifier-enhanced resonant photoacoustic spectroscopy (PAS) sensor is developed for sub-ppb level acetylene (C2H2) detection. The photoacoustic excitation source is composed of a telecommunication distributed feedback (DFB) laser and an erbium-doped fiber amplifier (EDFA). The weak photoacoustic second-harmonic signal is demodulated by a field-programmable gate array (FPGA) based lock-in amplifier. For sensitivity improvement, wavelength modulation spectrum and wavelet denoising methods are employed. The PAS sensor is optimized in terms of resonant frequency and current modulation depth for C2H2 detection at the wavelength of 1532.83 nm. The linearity of the sensor response to the laser power and C2H2 concentration confirms that saturation does not occur with the excitation power less than 1 W. With 1 W excitation power and 60 s averaging time, the detection limit (1δ) is achieved to be 0.37 ppb, which is the best value compared with other photoacoustic C2H2 sensors ever reported so far.

Detection of nitrous oxide by resonant photoacoustic spectroscopy based on mid infrared quantum cascade laser

Atmospheric greenhouse gases have great influence on the climate forcing, which is important to human being and also for natural systems. Nitrous oxide (N2O), such as carbon dioxide and methane, is an important greenhouse gas. It plays an important role in the atmospheric environment. Therefore, sensitive measurement of N2O concentration is of significance for studying the atmospheric environment. In this paper, a photoacoustic spectroscopy (PAS) system based on 7.6 m mid infrared quantum cascade laser combined with resonant PAS technique is established for the sensitive detection of N2O concentration. The PAS has been regarded as a highly sensitive and selective technique to measure trace gases. Compared with laser absorption spectroscopy, the PAS offers several intrinsic attractive features including ultra-compact size and no cross-response of light scattering. In addition, the signal of PAS is recorded with low-cost wavelength-independent acoustic transducer. The performance of the developed system is optimized and improved based on the traditional photoacoustic spectroscopic detection. Dual beam enhancement method is used to increase the effective optical power which effectively improves the detection sensitivity of the system. The N2O absorption line at 1307.66 cm-1 is chosen as the target line, and an operation pressure of 50 kPa is selected for reducing cross-talking from H2O absorption line. By detecting the photoacoustic signals of a certain concentration of N2O at different modulation frequencies and modulation amplitudes, the optimal modulation frequency and modulation amplitude of the system are determined to be 800 Hz and 90 mV, respectively. Different concentrations of N2O gas are detected under the optimized parameters, and calibration curve of the system, that is, the curve of photoacoustic signal versus concentration of N2O is obtained, which shows good linearity. The experimental results show that the minimum detection limit of the system is 150 ppb at a pressure of 50 kPa with an integration time of 30 ms. The system noise can be further reduced by increasing the averaging time. A minimum detection limit of 37 ppb is achieved by averaging signals 100 times, and the signal of N2O in the atmosphere is obtained.

Acoustic Modal Analysis of Resonant Photoacoustic Spectroscopy with Dual-Wavelength Differential Detection for Noninvasive Glucose Monitoring

A theoretical study of resonant photoacoustic spectroscopy (PAS) for glucose noninvasive detection was performed by rigorously taking into account the spatial distribution of the photothermal source and the acoustic resonance mode in a cavity. The sensitivity of the dual-wavelength differential PA technique is derived when glucose with weak optical absorption is detected in solution with high optical absorption. The sensitivity dependence of acoustic resonance modes was evaluated by both analysis and experiment with pure water. The analytical results show good agreement with the experiment. The sensitivity against the concentration of the target molecules can be enhanced approximately twofold by choosing the optimum acoustic resonance mode. The results indicate that this method has the potential to detect glucose in a physiological range comparable to that of invasive blood glucose monitoring.

Theoretical analysis of a resonant quartz-enhanced photoacoustic spectroscopy sensor

In this paper, we report the first analytical model for quartz-enhanced photoacoustic spectroscopy in combination with an acoustic resonator. A generalized fundamental equation is proposed to model the photoacoustic effect, taking into account the coupling between the tuning fork and the surrounding fluid. The analytical signal-to-noise ratio is derived, yielding a direct physical insight with respect to the system design. Experimental behaviors are very well reproduced, and numerical finite elements methods are implemented to successfully confirm the relevance of our approach. We also provide a detailed explanation of the coupling dynamics between the quartz tuning fork and the acoustically resonant tube.

Photoacoustic Detection of Perfluorocarbon Tracers in Air for Application to Leak Detection in Oil-Filled Cables

The underground oil-filled cable consists of a hollow copper conductor surrounded by oiled paper which acts as electrical insulation. The oil flows along the conductor and diffuses through it to the insulating paper. A lead sheath is used as the outer retaining wall. As the deterioration of this cover may cause a loss of insulation fluid, its detection is very important since this high voltage and power cable is used in cities even under sidewalks. The method of perfluorocarbon vapor tracers, based on the injection and subsequent detection of these volatile chemical substances in the vicinity of the cable, is one of the most promising methods, so far used in combination with gas chromatography and mass spectrometry. In this study, the possibility of detecting two different tracers, \(\mathrm{C}_{6}\mathrm{F}_{12}\) and \(\mathrm{C}_{7}\mathrm{F}_{14}\), by means of resonant photoacoustic spectroscopy is studied. The beam from a tunable amplitude-modulated \(\mathrm{CO}_{2}\) laser goes through an aluminum cell with quarter wave filters at both ends of an open resonator and an electret microphone in its center, attached to the walls. The calibration of the system for either substance diluted in chromatographic air showed a higher sensitivity for \(\mathrm{C}_{7}\mathrm{F}_{14}\), so the experiment was completed checking the behavior of this substance in samples prepared with ambient air in order to analyze the application of the system to field studies.

Cavity-enhanced resonant photoacoustic spectroscopy with optical feedback cw diode lasers: A novel technique for ultratrace gas analysis and high-resolution spectroscopy

Cavity-enhanced resonant photoacoustic spectroscopy with optical feedback cw diode lasers (OF-CERPAS) is introduced as a novel technique for ultratrace gas analysis and high-resolution spectroscopy. In the scheme, a single-mode cw diode laser (3 mW, 635 nm) is coupled into a high-finesse linear cavity and stabilized to the cavity by optical feedback. Inside the cavity, a build-up of laser power to at least 2.5 W occurs. Absorbing gas phase species inside the cavity are detected with high sensitivity by the photoacoustic effect using a microphone embedded in the cavity. To increase sensitivity further, coupling into the cavity is modulated at a frequency corresponding to a longitudinal resonance of an organ pipe acoustic resonator (f=1.35 kHz and Q approximately 10). The technique has been characterized by measuring very weak water overtone transitions near 635 nm. Normalized noise-equivalent absorption coefficients are determined as alpha approximately 4.4x10(-9) cm(-1) s(1/2) (1 s integration time) and 2.6x10(-11) cm(-1) s(1/2) W (1 s integration time and 1 W laser power). These sensitivities compare favorably with existing state-of-the-art techniques. As an advantage, OF-CERPAS is a "zero-background" method which increases selectivity and sensitivity, and its sensitivity scales with laser power.

High-sensitivity detection of hazardous SO2 using 266 nm UV laser

Pulsed laser resonant photoacoustic spectroscopy was applied for detection of highly toxic SO2 with 266 nm as the excitation source. An extra-cavity longitudinal resonant cell, was designed and fabricated to enhance the sensitivity of the system, which is capable of detecting the trace amount of SO2. As a process of signal-to-noise ratio optimization, the parametric dependence of the PA signal was carried out and the sensitivity achieved with our system was as low as 4 ppb, which is considered to be a sufficient level for the detection of ambient SO2 in the atmosphere. This study could be an antecedent for the design of a portable SO2 sensor.

Highly sensitive and mobile TDL-PA spectroscopic measuring device for methane

A mobile, reliable and highly sensitive measuring system for on-line outdoor measurements of methane is described using tunable diode laser resonant photoacoustic (TDL-PA) spectroscopy. The light source is a distributed feedback laser diode for selective detection of methane in ambient conditions via the 2v 3 -band transition at 1650.957 nm. A strong influence of humidity on the photoacoustic signal was observed due to a kinetic cooling effect caused by second order collisions of methane in the presence of oxygen. The measuring device has been used successfully in various field measurements. Very good correlations have been found between TDL-PA and commercial none dispersive infrared spectroscopic as well as gas chromatographic measurements. We realized an excellent linearity (R 2 = 0.999988) over three orders of magnitude for the concentration measurements with a detection limit (triple standard deviation) of 115 ppbv methane.

Applications of quartz tuning forks in spectroscopic gas sensing

A recently introduced approach to photoacoustic detection of trace gases utilizing a quartz tuning fork (TF) as a resonant acoustic transducer is described in detail. Advantages of the technique called quartz-enhanced photoacoustic spectroscopy (QEPAS) compared to conventional resonant photoacoustic spectroscopy include QEPAS sensor immunity to environmental acoustic noise, a simple absorption detection module design, and its capability to analyze gas samples ∼1mm3 in volume. Noise sources and the TF properties as a function of the sampled gas pressure, temperature and chemical composition are analyzed. Previously published results for QEPAS based chemical gas sensing are summarized. The achieved sensitivity of 5.4×10−9cm−1W∕√Hz is compared to recent published results of photoacoustic gas sensing by other research groups. An experimental study of the long-term stability of a QEPAS-based ammonia sensor is presented. The results of this study indicate that the sensor exhibits very low drift, which allows data averaging over >3h of continuous concentration measurements. Architecture and practical implementation of autonomous QEPAS-sensor controller electronics is described. Future developments of QEPAS technique are outlined.