Cantilever-enhanced Photoacoustic Spectroscopy Research Articles

Noncontact Fiber-Optic Cantilever-Enhanced Photoacoustic Spectroscopy.

Conventional cantilever-enhanced photoacoustic spectroscopy (CEPAS) usually requires the cantilever to be in contact with the gas, which limits its application in dusty and corrosive gas sensing. To overcome this challenge, this paper proposes noncontact fiber-optic cantilever-enhanced photoacoustic spectroscopy (NCFO-CEPAS) for high-sensitivity trace gas analysis. A polyethylene film with corrosion-resistant properties is affixed to the end of the cantilever acoustic sensor, and the effect of the distance between the polyethylene film and the cantilever acoustic sensor on the sensitivity of the system is analyzed by finite element analysis. Compared to the conventional CEPAS, NCFO-CEPAS has a lower background noise deviation. Besides, the potential damage to the silicon cantilever beam by corrosive gases can be avoided as the gas to be measured is not in contact with the silicon cantilever beam, and the gap of the cantilever beam will not be blocked in a high dust environment. Experimental results show that the detection limit of C2H2 gas is 0.5 ppm, and the normalized noise equivalent absorption coefficient reaches 5.93 × 10-9 cm-1 W Hz-1/2. The NCFO-CEPAS technique has the advantages of noncontact remote gas monitoring, not being corroded by gases, and high resistance to electromagnetic interference.

Photoacoustic phase-controlled Fourier-transform infrared spectroscopy

We demonstrate a 13-fold speed improvement in broadband cantilever-enhanced photoacoustic spectroscopy (CEPAS) by combining it with phase-controlled Fourier-transform spectroscopy (PC-FTS) instead of traditional Fourier-transform infrared spectroscopy (FTIR). PC-FTS is a modification of FTIR and capable of fundamentally faster interferogram acquisitions. The speed-improvement is beneficial for CEPAS, which is an especially sensitive version of the background-free photoacoustic spectroscopy technique. We used the PC-FTS-CEPAS technique to measure the absorption spectrum of methane in the mid-infrared region (3.3–3.5 µm) with an optical frequency comb as the light source.

Cantilever-enhanced photoacoustic measurement of HTO in water vapor

A photoacoustic detection of tritiated water (HTO) is presented. The method uses cantilever-enhanced photoacoustic spectroscopy (CEPAS) to reach sub-ppb sensitivity for HTO in the gas phase. A noise equivalent concentration of 0.88 ppb is reached with a sampling time of 1 min. The high performance and small sample volume of CEPAS allows sensitive detection of HTO from a sample with low total activity.

Enhancement of photoacoustic spectroscopy with sorption enrichment for ppt-level benzene detection.

A real-time trace gas detector for benzene is demonstrated. The measurement system takes advantage of modest enrichment through short adsorption periods to reach a ppt-level detection limit with a sampling cycle of 90 s, which includes sample adsorption, desorption, and a spectroscopic measurement. Benzene is collected on Tenax TA sorbent for 30 s and then detected from the enriched samples with photoacoustic spectroscopy. High sensitivity is achieved using cantilever-enhanced photoacoustic spectroscopy and a continuous-wave quantum cascade laser emitting at 14.8 µm wavelength, which corresponds to the absorption wavelength of the strongest benzene infrared band. We reach a detection limit of 150 ppt of benzene, over one sampling cycle. Interference from humidity and other common petrochemicals is evaluated.

High-Sensitivity Silicon Cantilever-Enhanced Photoacoustic Spectroscopy Analyzer with Low Gas Consumption.

A silicon cantilever-enhanced photoacoustic spectroscopy (PAS)-based trace gas analyzer with low gas consumption is presented. A silicon cantilever-based fiber-optic Fabry-Perot (F-P) interferometric acoustic sensor with a compact structure and high sensitivity is designed for photoacoustic signal detection. The non-resonant photoacoustic cell (PAC) is a cylindrical copper tube with a volume of 0.56 mL. A near-infrared laser with a center wavelength of 1532.83 nm amplified using an erbium-doped fiber application amplifier is used as the excitation light. The wavelength modulation spectroscopy (WMS) technique is employed in the present work for second-harmonic photoacoustic signal detection. The experimental results show that the minimum detection limit of C2H2 is 199.8 parts per trillion (ppt) with an average time of 60 s. The normalized noise equivalent absorption coefficient is calculated as 1.72 × 10-9 cm-1 W/Hz1/2. Furthermore, the proposed silicon cantilever-enhanced non-resonant PAS-based gas analyzer can not only analyze the gas concentration in a closed small-capacity PAC with low gas consumption but also detect target gas leakage in real time at a long distance.

Radiocarbon dioxide detection using cantilever-enhanced photoacoustic spectroscopy.

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.

Quantification of Proton Radiation Damage in Polyimide Aerogel by Cantilever-Enhanced Photoacoustic Spectroscopy

Charged particles radiation induces the performances degradation of space polyimide (PI) aerogel, which puts forward the requirement for the accurate quantification of the radiation-induced damage. Photoacoustic spectroscopy (PAS) was proposed with a cantilever for the sensitive resonance detection of the photoacoustic (PA) pressure based on the analysis of cantilever-air dynamic coupling theory and finite element simulation. Wavelength scan PAS inspection of the proton irradiated PI aerogel verified the sensitivity of PA signals to the radiation fluence. Dual-wavelength PAS was first theoretically investigated and performed by measuring the PA signals alternately induced by the 405- and 532-nm lasers. Based on the presented theoretical relation between the PA signals and the radiation characteristics, the derived normalized damage fraction ( $f_{a}$ ) revealed distinct reliance on the proton fluence ( $\phi$ ). The experimental results and the theoretical relations fit well on the goodness of $\chi ^{2} = 8.2 \times 10^{-4}$ , and the fit value of the single-proton damage area ( $\sigma$ ) was $1.4\times 10^{-16}$ cm2. The relative error for the measurement of fluence ( $\phi$ ) was 5%. The research indicates that the presented cantilever-enhanced PAS method is an efficient tool for rapid and accurate quantification of the proton radiation-induced damage in PI aerogel.

Simultaneous Detection of C₂H₂ and CO Based on Cantilever-Enhanced Photoacoustic Spectroscopy

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.

Sub-ppb detection of benzene using cantilever-enhanced photoacoustic spectroscopy with a long-wavelength infrared quantum cascade laser.

We report a novel, to the best of our knowledge, photoacoustic spectrometer for trace gas sensing of benzene. A quantum cascade laser emitting at the wavelength 14.8 µm is used as the light source in the spectroscopic detection. This wavelength region contains the strongest vibrational band of benzene, which is free of spectral overlap from common trace gases, making it a strong candidate for sensitive benzene detection. Cantilever-enhanced photoacoustic spectroscopy is used for detection. This simple and robust measurement setup can reach a benzene detection limit below 1 ppb.

Broadband Laser-Based Infrared Detector for Gas Chromatography.

Cantilever-enhanced photoacoustic spectroscopy coupled with gas chromatography is used to quantitatively analyze a mixture of alcohols in a quasi-online manner. A full identification and quantification of all analytes are achieved based on their spectral fingerprints using a widely tunable continuous-wave laser as a light source. This can be done even in the case of interfering column/septum bleed or simultaneously eluted peaks. The combination of photoacoustic spectroscopy and gas chromatography offers a viable solution for compact and portable instruments in applications that require straightforward analyses with no consumables.

Trace Ammonia Detection Based on Near-Infrared Fiber-Optic Cantilever-Enhanced Photoacoustic Spectroscopy

A trace ammonia (NH3) detection system based on the near-infrared fiber-optic cantilever-enhanced photoacoustic spectroscopy (CEPAS) is proposed. A fiber-optic extrinsic Fabry-Perot interferometer (EFPI) based cantilever microphone has been designed to detect the photoacoustic pressure signal. The microphone has many advantages, such as small size and high sensitivity. A near-infrared tunable erbium-doped fiber laser (EDFL) amplified by an erbium-doped fiber amplifier (EDFA) is used as a photoacoustic excitation light source. To improve the sensitivity, the photoacoustic signal is enhanced by a photoacoustic cell with a resonant frequency of 1624 Hz. When the wavelength modulation spectroscopy (WMS) technique is applied, the weak photoacoustic signal is detected by the second-harmonic detection technique. Trace NH3 measurement experiments demonstrate that the designed fiber-optic CEPAS system has a linear response to concentrations in the range of 0 ppm – 20 ppm at the wavelength of 1522.448 nm. Moreover, the detection limit is estimated to be 3.2 ppb for a lock-in integration time of 30 s.

Cavity-enhanced cantilever-enhanced photo-acoustic spectroscopy.

We have improved the sensitivity of a state-of-the-art cantilever-enhanced photo-acoustic trace gas sensor by combining it with an optical power build-up cavity. The build-up cavity enhances the photo-acoustic signal by a factor of ∼100, resulting in an exceptionally good normalised noise equivalent absorption (NNEA) value of 1.75 × 10-12 W cm-1 Hz-1/2. We demonstrate the sensor platform in the 1530 nm wavelength range with a simple distributed feedback diode laser, achieving 75 ppt sensitivity for C2H2 with a 10 s integration time.

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

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

A novel photoacoustic spectroscopy gas sensor using a low cost polyvinylidene fluoride film

A proof-of-concept gas sensor based on innovative photoacoustic spectrophone was introduced for purpose of developing a low cost and simple configuration photoacoustic spectroscopy gas sensor and demonstrated, in which the photoacoustic signal was detected with a low cost polyvinylidene fluoride (PVDF) film being used as transducer, instead of using conventional microphone or quartz tuning fork. In such a PVDF-based photoacoustic spectroscopy (PVDF-PAS) approach, the PVDF film plays a role both as a cantilever used in cantilever-enhanced photoacoustic spectroscopy and as a piezoelectric quartz tuning fork used in quartz-enhanced photo-acoustic spectroscopy. Feasibility of the introduced PVDF-PAS for trace gas sensing was demonstrated by measuring H2O vapor with a minimum detection limit of 40 ppmv using a lock-in time constant of 30 ms, this corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 2.4 × 10−7 cm-1W/Hz1/2. The use of polyvinylidene fluoride film as transducer for photoacoustic signal sensing offers good flexibility, water resistance, chemical stability and low cost for applications under harsh or/and specific environmental conditions.

Cantilever-Enhanced Photoacoustic Detection and Infrared Spectroscopy of Trace Species Produced by Biomass Burning

The applicability of cantilever-enhanced photoacoustic spectroscopy (CEPAS), which exploits the unique properties of a micromechanical lever sensor (cantilever) in combination with tunable quantum ...

Sub-parts-per-trillion level sensitivity in trace gas detection by cantilever-enhanced photo-acoustic spectroscopy

An exceptional property of photo-acoustic spectroscopy is the zero-background in wavelength modulation configuration while the signal varies linearly as a function of absorbed laser power. Here, we make use of this property by combining a highly sensitive cantilever-enhanced photo-acoustic detector, a particularly stable high-power narrow-linewidth mid-infrared continuous-wave optical parametric oscillator, and a strong absorption cross-section of hydrogen fluoride to demonstrate the ability of cantilever-enhanced photo-acoustic spectroscopy to reach sub-parts-per-trillion level sensitivity in trace gas detection. The high stability of the experimental setup allows long averaging times. A noise equivalent concentration of 650 parts-per-quadrillion is reached in 32 minutes.

Cantilever-enhanced photoacoustic spectroscopy applied in the research of natural and synthetic calcium phosphate

This study demonstrates the significant potential of cantilever-enhanced Fourier transform infrared photoacoustic spectroscopy (FTIR PAS) principles. The improved sensitivity and reproducibility of this method presents a potent tool in the study of biomaterials. The article discusses aspects of the application of cantilever-enhanced FTIR PAS in the research of natural and biological calcium phosphate and the statistical evaluation of the FTIR PAS sampling method. The improved constructions of the FTIR PAS accessory reduce limitations of the conventional capacitive microphone and provide a sensitive tool for samples or processes unreachable by more traditional transmittance methods, or ATR sampling technique. The most common and important applications have been discussed in-depth to show the wide range of problems solved by FTIR PAS.

Parts-per-trillion-level detection of nitrogen dioxide by cantilever-enhanced photo-acoustic spectroscopy.

We present a simple and highly sensitive cantilever-enhanced photo-acoustic sensor for detection of nitrogen dioxide. A noise equivalent detection limit of 50 parts-per-trillion in 1 s is demonstrated. The limit was reached with an average optical power of 4.7 W using a continuous-wave laser at 532 nm. The achieved normalized noise equivalent absorption coefficient was 2.6×10(-10) W cm(-1) Hz(-1/2).

All-Optical Cantilever-Enhanced Photoacoustic Spectroscopy in the Open Environment

A novel all-optical cantilever-enhanced photoacoustic spectroscopy technique for trace gas detection in the open environment is proposed. A cantilever is set off-beam to “listen to” the photoacoustic signal, and an improved quadrature-point stabilization Fabry–Perot demodulation unit is used to pick up the vibration signal of the acoustic transducer instead of a complicated Michelson interferometer. The structure parameters of the cantilever are optimized to make the sensing system work more stably and reliably using a finite element method, which is then fabricated by surface micro-machining technology. Finally, related experiments are carried out to detect the absorption of water vapor at one atmosphere in the open environment. It was found that the normalized noise-equivalent absorption coefficient obtained by a traditional Fabry–Perot demodulation unit is \(3.38 \times 10^{-7}\,\hbox {cm}^{-1}\cdot \hbox {W}\cdot \hbox {Hz}^{-1/2}\), while that by a quadrature- point stabilization Fabry–Perot demodulation unit is \(1.08 \times 10^{-7}\,\hbox {cm}^{-1}\cdot \hbox {W}\cdot \hbox {Hz}^{-1/2}\), which indicates that the sensitivity is increased by a factor of 3.1 using improved cantilever-enhanced photoacoustic spectroscopy.

Broadly tunable quantum cascade laser in cantilever-enhanced photoacoustic infrared spectroscopy of solids

An external cavity quantum cascade laser (EC-QCL) is applied in the photoacoustic detection of solid samples. The EC-QCL used has a broad tuning range of 676 cm−1 (970–1,646 cm−1) in the mid-infrared region, which enables accurate broadband spectroscopy of large molecules. The high spectral power density of the EC-QCL is combined with an extremely sensitive optical cantilever microphone of the photoacoustic detector to achieve an ultimate sensitivity. The carbon black, polyethylene, and hair fiber samples were measured with the EC-QCL photoacoustic detection using electrical amplitude modulation to demonstrate the possibilities of the setup. The same measurements were repeated with a Fourier transform infrared (FTIR) spectrometer combined with a photoacoustic detector for a comparison. The EC-QCL photoacoustic setup yielded roughly a decade better signal-to-noise ratios than the FTIR setup with the same measurement time.