Skip to main content
NCBI home page
Photoacoustics logoLink to Photoacoustics
. 2025 Jan 10;42:100686. doi: 10.1016/j.pacs.2025.100686

A light-induced thermoelastic spectroscopy using surface mounted device quartz tuning fork

Shaoqiang Bi 1, Xinru Zhang 1, Zhonghai Zhang 1, Xuan Liu 1, Lu Qin 1, Jingqi Shi 1, Yiyang Zhao 1, Zongliang Wang 1,⁎
PMCID: PMC11795151  PMID: 39911776

Abstract

This paper reported on a system for the detection of trace acetylene (C2H2) gas utilizing a surface mounted device quartz tuning fork (SMD QTF) in conjunction with light-induced thermoelastic spectroscopy (LITES) and provided a comparative analysis against a conventional plug-in quartz tuning fork (P-QTF). The SMD QTF is a cost-effective standard instrument featuring a transparent glass shell and smaller size, which eliminates the need for stripping shell in LITES and effectively mitigates oxidation of the QTF as well as drift in resonance frequency. The SMD QTF has almost 2–4 times more Q factor than the conventional bare P-QTF. Experiments demonstrated that the signal amplitude of the SMD-QTF was almost 9 times higher than that of the conventional bare P-QTF. Minimum detection limits (MDLs) of 68.11 ppb@220 s (P-QTF) and 40.39 ppb@200 s (Larger SMD QTF) were obtained for both under the same experimental conditions.

Keywords: Light-induced thermoelastic spectroscopy, Quartz tuning fork, Gas sensing, Absorbing gas cell

1. Introduction

The detection of specific gases in a range of industrial, aerospace, medical and exploration scenarios has become increasingly important in recent years. Among the various detection solutions available, optical gas detection technology [1], [2], [3], [4], [5] has garnered considerable attention, due to its non-invasive and real-time detection capabilities. Tunable diode laser absorption spectroscopy (TDLAS) based on Beer Lambert's law constitutes a well-established optical detection method. It utilizes a photodetector to detect the light intensity at the wavelength of the gas absorption peak after passing through the gas cell [6], [7]. However, the photodetectors currently in service are not only expensive, limited by material constraints and limited in detection wavelengths, and prone to power saturation [8], [9]. In recent years, light-induced thermoelastic spectroscopy (LITES) has been proposed as an alternative, with the aim of using quartz tuning forks (QTF) with thermoelastic vibration effect and piezoelectric effect instead of photodetectors as light receivers [10]. The QTF with a frequency of approximately 32.7 kHz and is a component of a commercially available cylindrical quartz crystal oscillator. It is a fork-shaped quartz crystal coated with an electrically conductive layer of silver, which converts and amplifies received signals mainly by using the possessed piezoelectric and resonant effects. Furthermore, it was initially proposed as an alternative to microphones in photoacoustic spectroscopy (PAS) [11], and subsequently employed extensively in quartz enhancement photoacoustic spectroscopy (QEPAS) [12], [13], [14], [15], [16], [17], [18] for gas sensing due to its advantages of high detection sensitivity and small size.

The QTF not only has low cost and high Q factor, and possesses full wavelength response and high photoelectric sensitivity [19], but also not prone to power saturation [20], [21]. There are many reports on the trace detection of various gases and compounds using LITES [22], [23], [24], and these reports fully demonstrate the prospects and advantages of LITES in the field of gas detection. In addition, there are additional methods for enhancing detection accuracy beyond extending the optical length of the absorbing gas cell. From a laser perspective, LITES requires the laser beam to be incident on the surface of the QTF, which leads to the introduction of background noise inevitably. Consequently, the detection accuracy can be enhanced by reducing laser noise. The introduction of a phase-reversed reference light [25], [26], the use of the self-differential characteristics of the QTF [27] and the recently proposed 2f/1f wavelength modulation spectroscopy (2f/1f-WMS) technique [28] are all methods that can effectively improve detection accuracy. From the perspective of the QTF, there are two main methods to improve detection accuracy, one is to improve the absorption efficiency of the QTF for laser light, which is usually achieved by etching the electrically conductive layer of silver with high reflectivity [29] or plating a film with high absorption on the surface of the QTF [30], [31], [32]. The second is to use a custom QTF [33], [34], [35] instead of the conventional standard QTF. Meanwhile, the frequency of the custom QTF is designed to be lower than that of the standard QTF for obtaining a longer energy accumulation time, while the conductive layer coating is replaced by a gold film, which avoids oxidation and frequency drift problems. While the custom QTF has high detection sensitivity, the manufacturing process is arduous and the cost is considerably higher than that of the standard QTF.

In this paper, a commercially available surface mounted device (SMD) QTF was proposed for developing high-sensitivity trace gas detection. Compared to the conventional plug-in quartz tuning fork (P-QTF), the SMD QTF is easier to use without removing the shell and possesses smaller size and higher Q factor. Due to the protection of shell, the SMD QTF can avoid the deviation of resonance frequency in long-term operation, providing high working stability. Firstly, the dimensional appearance of several standard QTFs were shown, and Q factors of various QTFs were investigated using electrical modulation technique, a larger SMD QTF (L-SMD QTF) was chosen for the experimental demonstration due to its higher Q factor (almost 4 times more Q factor than the conventional bare P-QTF). After optimizing the incident position of the laser, gas detection experiments were carried out with acetylene (C2H2) as the sample gas. The results showed the L-SMD QTF had a higher signal amplitude and additional noise, in a comprehensive comparison, the detection effect of the L-SMD QTF was still superior to that of the P-QTF.

2. Comparison of quartz tuning forks

The physical drawing of three types of QTFs is presented in Fig. 1(a): on the left is the traditional bare P-QTF,whose shell has been removed, in the middle is the smaller SMD QTF (S-SMD QTF) (Epson FC-135, 3.2 mm × 1.5 mm × 0.8 mm), and on the right is the larger SMD QTF (L-SMD QTF) (Epson FC-225, 4.9 mm × 1.8 mm × 0.8 mm). It is important to note that the surface of both SMD QTFs feature clear glass, and that any silk-screened marking on their glass shells have been removed manually. The silkscreen markings on the top of the SMD QTF's shell were removed by gently rubbing it with metal tweezers, and then wiping off the residual powder on the surface with an alcohol swab. The detailed dimensional drawings of P-QTF, S-SMD QTF, and L-SMD QTF are provided in Fig. 1(b)–(d), respectively.

Fig. 1.

Fig. 1

Open in a new tab

(a) Physical representations of three QTFs. (b) Dimensions drawing of the P-QTF. (c) Dimensions drawing of the S-SMD QTF. (d) Dimensions drawing of the L-SMD QTF.

The traditional intact P-QTF features an impermeable shell that has to be removed for use. Stripping the shell results in a deviation of the center frequency and a significant reduction in the Q factor. Fig. 2 illustrates the resonant frequency response fitting curves of four types of QTFs measured by electrical modulation. Specifically, Fig. 2(a)–(d) corresponded to the bare P-QTF, S-SMD QTF, L-SMD QTF and the intact P-QTF, with their corresponding Q factors of 10,992, 19,893, 38,322 and 58,508, respectively. The Q factor used in this paper is calculated as:

Q=f0w/2 (1)

where f0 is the centre resonant frequency of the QTF and w is full width at half maxima (FWHM). The asymmetry of resonant frequency response curve is due to the presence of parasitic capacitance. A higher Q factor indicates lower vibration loss and greater energy utilization efficiency. To facilitate comparison with the traditional P-QTF, subsequent experiments employed the L-SMD QTF due to its superior Q factor over that of the S-SMD QTF.

Fig. 2.

Fig. 2

Open in a new tab

Fitted curves of resonant frequency response of four kinds of QTFs by electrical modulation. (a) Bare P-QTF. (b) S-SMD QTF. (c) L-SMD QTF. (d) Intact P-QTF.

3. Experimental setup

The schematic configuration of the QTF-based gas sensor system is illustrated in Fig. 3. C2H2 was utilized as the experimental sample gas, with a 1532 nm DFB laser selected as the light source. The absorption peak of C2H2 was identified at 1532.83 nm, exhibiting a line intensity of 2.3 × 10−20 cm/molecule. The laser was operated at a fixed temperature of 23 °C, with a current tuning range of 62–90 mA and a laser output power of 10.3 mW at the peak acetylene absorption wavelength. A low-frequency sawtooth wave (100 ms) and a high frequency sine wave (corresponding to half of the center frequency of the employed QTF) were generated by the signal generator and subsequently input into the laser controller (LDC501, Stanford Research Systems) after superimposition to achieve wavelength modulation. The laser beam traversed an absorbing gas cell with an optical length of 0.5 m before being directed onto the surface of the QTF via a fiber collimator (spot diameter: 0.2 mm, working distance: 20 mm). A custom-designed transimpedance amplifier circuit board converted and amplified the current output from the QTF into a voltage, which was then transmitted to a lock-in amplifier (Zurich Instruments) for second harmonic (2f) demodulation. The demodulation frequency was set equal to the center frequency of the QTF used, while the equivalent bandwidth was set to 2.55 Hz. Then the demodulated signals were sent to a computer for concentration calculation and display. The experiments were conducted on both traditional P-QTF and L-SMD QTF, respectively.

Fig. 3.

Fig. 3

Open in a new tab

Schematic configuration of the QTF-based gas sensing system.

4. Results and discussion

The surface of the QTF is coated with a highly reflective silver layer that facilitates electrical conduction, however, this coating may reduce the laser absorption efficiency. Additionally, the thermoelastic vibration effect due to temperature changes generated at different positions of the QTF also varies. Therefore, it is essential to optimize the laser incident position of the L-SMD QTF prior to conducting experimental measurements. The experiments were conducted under ambient temperature and pressure conditions, The total gas flow rate was regulated by a flow controller set at 100 mL/min, while the concentration of C2H2 in the absorption gas cell was maintained at 1000 ppm by adjusting the ratio of nitrogen (N2) and C2H2 gases flow rates. A precision displacement translator was employed to reposition the fiber collimator for modifying the laser incident position. The scanning range for the displacement was adjusted to exceed that of the L-SMD QTF dimensions due to the non-negligible laser spot diameter. Fig. 4 illustrates 3D curved depicting the amplitude of 2f signals as a function of varying laser incidence positions. Referring to the azimuthal direction of Fig. 1, a length of 1 mm was measured on the X-axis at 0.1 mm intervals and a length of 4 mm was measured on the Y-axis at 0.2 mm intervals. The coordinates yielding the highest signal coordinates were identified as (0.5 mm, 1 mm, 26,531 μV) which in combination with the coordinate definition in Fig. 1(d). Subsequent experiments were conducted in the optimal incidence position. For P-QTF measurements, no positional optimization scans were performed and we directly utilized conventional optimal incidence position at the root of the P-QTF.

Fig. 4.

Fig. 4

Open in a new tab

3D curved surface diagram of the laser incident position response for the L-SMD QTF.

In order to minimize the interference of external environmental factors on the signal, wavelength modulation spectroscopy (WMS) was employed for gas concentration sensing. Consequently, it is essential to optimize the amplitude of the modulation signal prior to the experiments in order to align with the gas absorption peak to achieve the optimal signals. At a fixed C2H2 gas concentration of 1000 ppm, Fig. 5 illustrates the normalized 2f signal amplitudes of both P-QTF and L-SMD QTF as a function of the amplitude of the high-frequency sinusoidal waveform. Both QTFs attained a maximum amplitude when the amplitude of the modulation signal was set 0.23 V. Therefore, in the subsequent experiments, the amplitude of the modulating sinusoidal waveform was established into 0.23 V.

Fig. 5.

Fig. 5

Open in a new tab

Normalized signal amplitude as a function of modulating signal amplitude.

To assess the gas sensing performance of the P-QTF and L-SMD QTF, the gas concentration in the absorbing gas cell was systematically varied from 200 to 1000 ppm. The corresponding 2f signals of the P-QTF and L-SMD QTF at different concentrations are illustrated in Fig. 6(a) and (b). At a concentration of 1000 ppm, the amplitudes of these signals were measured at 3.11 mV for the P-QTF and 27.05 mV for the L-SMD QTF, respectively. The signal amplitude of the L-SMD QTF was almost 9 times that of the P-QTF. The linearity of concentration response for both QTFs across varying concentrations is depicted in Fig. 6(c), where R2 values are recorded as 0.990 for the P-QTF and 0.994 for the L-SMD QTF, indicating strong linear relationships between signal amplitude and gas concentration. Fig. 6(d) presents noise measurements of both QTFs under pure N2 conditions over a duration for 20 s, one standard deviation (1σ) noise levels were found to be 2.10 μV for the P-QTF and 7.21 μV for the L-SMD QTF. Based on the above data, we calculated that at 1000 ppmC2H2 concentration, the signal-to-noise ratios (SNR) were approximately 1480 for the P-QTF and 3751 for the L-SMD QTF, suggesting superior performance by the L-SMD QTF. These findings indicate the while laser incidence on the L-SMD QTF generates a higher piezoelectric current, it also introduces additional noise factors. The elevated noise levels observed with the L-SMD QTF may be attributed to the reflected and scattered light from the interaction of the laser with its shell and base, which acts on the QTF to introduce additional thermal noise.

Fig. 6.

Fig. 6

Open in a new tab

(a) 2f signals based on P-QTF for C2H2 at varying concentrations. (b) 2f signals based on L-SMD QTF based for C2H2 at varying concentrations. (c) Linear fitting of C2H2 gas concentration in relation to the 2f signal amplitude based on P-QTF and L-SMD QTF. (d) Pure N2 noise of P-QTF and L-SMD QTF.

To further evaluate the stability of the system, Allan deviation analysis was employed to calculate the long-term averaging noise at pure N2, Subsequently, the data were converted into detection limits. Fig. 7 shows the result of the Allan deviation for the P-QTF and L-SMD QTF. The findings indicate that the P-QTF achieves a minimum detection limit (MDL) of 68.11 ppb with an averaging time of 222 s and the L-SMD QTF demonstrates a MDL of 40.39 ppb with an averaging time of 200 s. Additionally, the normalized noise equivalent absorption (NNEA) is a critical evaluation criterion frequently used to assess gas sensors’ performance under normalized conditions. The calculated NNEA of both P-QTF and L-SMD QTF are 2.48 × 10−9 cm−1 W/√Hz and 9.77 × 10−10 cm−1 W/√Hz, respectively.

Fig. 7.

Fig. 7

Open in a new tab

Analysis of Allan deviation for the P-QTF and L-SMD QTF.

Several QTFs were selected for measurement to record their center frequencies and Q factors under the electrical modulation techniques. This process was repeated after a period of 30 days, and the recorded data is summarized in Table 1. It can be observed that the bare P-QTFs exhibited varying degrees of frequency drift, conversely, the center frequencies of SMD QTFs remained largely stable throughout this duration.

Table 1.

Frequency response parameters of different types of QTFs measured by electrical modulation.

QTF kinds f0 (Hz) w (Hz) Q factor f0 (Hz） (30 days later) w (Hz) Q factor Δf0 (Hz)
P-QTF#1 32,756.93 4.76 9733 32,757.90 4.56 10,173 0.93
P-QTF#2 32,757.03 4.09 11,328 32,756.13 4.31 10,739 − 0.90
P-QTF#3 32,758.21 4.02 11,525 32,756.74 4.36 10,635 − 1.47
S-SMD QTF#1 32,764.65 2.34 19,804 32,764.69 2.32 19,975 0.04
S-SMD QTF#2 32,764.55 2.31 20,061 32,764.61 2.33 19,889 0.06
L-SMD QTF#1 32,765.03 1.14 40,652 32,765.03 1.13 41,012 0
L-SMD QTF#2 32,765.00 1.27 36,491 32,765.03 1.25 37,074 0.03
Open in a new tab

5. Conclusions

In this paper, we presented the application of SMD QTF for trace gas sensing. Unlike bare P-QTFs, the SMD QTF can be utilized as a photodetector directly without the need to remove its protective shell. A comparison of the Q factors among various QTFs were conducted using the electrical modulation, revealing that the SMD QTF exhibited a higher Q factor than the traditional bare P-QTF. The L-SMD QTF was selected for the subsequent experiments due to its superior Q factor within the category of SMD QTFs. Subsequently, we optimized the position of laser incidence by employing the L-SMD QTF and compared its gas sensing performance with that of traditional P-QTFs, utilizing a DFB laser and wavelength modulation technique for C2H2 detection. The data indicated the signal amplitude of the L-SMD QTF was considerably higher than that of the P-QTF, but it exhibited slightly higher noise level. However, the overall performance of the L-SMD QTF surpassed that of the P-QTF, such as SNR (1480 for the P-QTF and 3751 for the L-SMD QTF) and MDL (68.11 ppb@222 s for the P-QTF and 40.39 ppb@200 s for the L-SMD QTF).

Traditional P-QTF require frequent calibration during practical applications because they are prone to frequency drift when exposed to air. Therefore, the bare P-QTF are unsuitable for long-term sensing applications. Currently developed custom-made QTFs are coated with gold or vacuum-sealed to solve the above issues, these approaches not only increase costs but also add complexity to the over process. The SMD QTF offers a cost-effective alternative by functioning effectively in an encapsulated state and is regarded as a promising research proposal.

CRediT authorship contribution statement

Shaoqiang Bi: Writing – original draft, Validation, Methodology, Formal analysis, Data curation. Lu Qin: Supervision. Xuan Liu: Methodology, Data curation. Zhonghai Zhang: Supervision, Data curation. Xinru Zhang: Methodology, Data curation. zongliang wang: Writing – review & editing, Supervision, Resources, Methodology. Yiyang Zhao: Supervision. Jingqi Shi: Supervision.

Funding

This work was supported by National Natural Science Foundation of China (62105133).

Declaration of Competing Interest

The authors declare that there are no conflicts of interest.

Biographies

graphic file with name fx1.jpg

Shaoqiang Bi received the B.S. degree in electronic information science and technology from Qingdao Agricultural University, Qingdao, China, in 2019, and the M.S. degree in the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China, in 2023. His current research interest is optical gas sensing.

graphic file with name fx2.jpg

Xinru Zhang received the B.S. degree in electronic information science an technology from Liaocheng University, Liaocheng, China, in 2023. She is currently pursuing the M.S. degree with the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China. His current research interest is the photothermal spectrum of optical fiber gas sensing.

graphic file with name fx3.jpg

Zhonghai Zhang received the B.S. degree in electronic information engineering from Liaocheng University, Liaocheng, China, in 2022. He is currently pursuing the M.S. degree with the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China. His current research interests include optical gas sensing.

graphic file with name fx4.jpg

Xuan Liu received the B.S. degree in Electronic Science and Technology from Shandong Technology and Business University, Yantai, China, in 2024. He is currently pursuing the M.S. degree with the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China. His current research interests include optical gas sensing.

graphic file with name fx5.jpg

Lu Qin received the B.S. degree in communication engineering from Liaocheng University, Liaocheng, China, in 2022. She is currently pursuing the M.S. degree with the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China. Her current research interest is fiber optic gas sensing technology.

graphic file with name fx6.jpg

Jingqi Shi received the B.S. degree in communication engineering from Liaocheng University, Liaocheng, China, in 2022. She is currently pursuing the M.S. degree with the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China. Her current research interest is laser-induced thermoelastic spectroscopy.

graphic file with name fx7.jpg

Yiyang Zhao received the B.S. degree in electronic information science and technology from Liaocheng University, Liaocheng, China, in 2021. He is currently pursuing the M.S. degree with the School of Physical Science and Information Technology, Liaocheng University, Liaocheng, China. His current research interest is multi-component gas detection.

graphic file with name fx8.jpg

Zongliang Wang received the Ph.D. degree from the School of Information Science and Engineering, Shandong University, Jinan, China, in july 2015. He is currently with the School of Physics Science and Information Technology, Liaocheng University, Liaocheng, China. His research interests include optical fiber sensors and fiber lasers, mainly including quartz-enhanced photoacoustic spectroscopy (QEPAS) gas sensors, infrared absorption spectroscopy gas sensors,and fiber intracavity gas sensors.

Data availability

Data will be made available on request.

References

  • 1.Jin W., et al. Recent advances in spectroscopic gas sensing with micro/nano-structured optical fibers. Photon. Sens. 2021;11:141. [Google Scholar]
  • 2.Han X., et al. Fiber-optic trace gas sensing based on graphite excited photoacoustic wave. Sens. Actuators B-Chem. 2024;408 [Google Scholar]
  • 3.Pan W., Zhang J., Dai J., Song K. Tunable diode laser absorption spectroscopy system for trace ethylene detection. Spectrosc. Spect. Anal. 2012;32(10):2875. [PubMed] [Google Scholar]
  • 4.Maithani S., Pradhan M. Cavity ring-down spectroscopy and its applications to environmental, chemical and biomedical systems. J. Chem. Sci. 2020;132(1):114. [Google Scholar]
  • 5.Chen B., Li H., Yin X., et al. Trace photoacoustic SO2 gas sensor in SF6 utilizing a 266 nm UV laser and an acousto-optic power stabilizer. Opt. Express. 2023;31(4):6974. doi: 10.1364/OE.483240. [DOI] [PubMed] [Google Scholar]
  • 6.Yang H., Chen J., Luo X. Leakage detection of closed vials based on two-line water-vapor TDLAS. Measurement. 2019;135:413. [Google Scholar]
  • 7.Dong L., Tittle F.K., et al. Compact TDLAS based sensor design using interband cascade lasers for mid-IR trace gas sensing. Opt. Express. 2016;24(6):A528. doi: 10.1364/OE.24.00A528. [DOI] [PubMed] [Google Scholar]
  • 8.Ma Y. Recent advances in QEPAS and QEPTS based trace gas sensing: a review. Front. Phys. 2020;8:268. [Google Scholar]
  • 9.Ding J., He T., Zhou S., et al. Quartz tuning fork-based photodetector for mid-infrared laser spectroscopy. Appl. Phys. B-Lasers Opt. 2018;124(5):78. [Google Scholar]
  • 10.Ma Y., et al. Quartz-tuning-fork enhanced photothermal spectroscopy for ultra-high sensitive trace gas detection. Opt. Express. 2018;26(24):32103–32110. doi: 10.1364/OE.26.032103. [DOI] [PubMed] [Google Scholar]
  • 11.Kosterev A.A., et al. Quartz-enhanced photoacoustic spectroscopy. Opt. Lett. 2002;27(21):1902. doi: 10.1364/ol.27.001902. [DOI] [PubMed] [Google Scholar]
  • 12.Zhang Q., Chang J. Pptv-level intra-cavity QEPAS sensor for acetylene detection using a high power Q-switched fiber laser. IEEE Sens. J. 2019;19(15):6181–6186. [Google Scholar]
  • 13.Zhang C., Qiao S., et al. Differential quartz-enhanced photoacoustic spectroscopy. Appl. Phys. Let. 2023;122(24) [Google Scholar]
  • 14.Ayache D., Trizpil W., Rousseau R., et al. Benzene sensing by quartz enhanced photoacoustic spectroscopy at 14.85 µm. Opt. Express. 2022;30(4):55315539. doi: 10.1364/OE.447197. [DOI] [PubMed] [Google Scholar]
  • 15.Fu L., Yang M., et al. Transient tracer gas measurements: development and evaluation of a fast- response SF6 measuring system based on quartz- enhanced photoacoustic spectroscopy. Indoor Air. 2022;32(1) doi: 10.1111/ina.12952. [DOI] [PubMed] [Google Scholar]
  • 16.Wu H., Dong L., Zheng H., et al. Beat frequency quartz-enhanced photoacoustic spectroscopy for fast and calibration-free continuous trace-gas monitoring. Nat. Commun. 2017;8:15531. doi: 10.1038/ncomms15331. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Wang J., Wu H., Dong L., et al. Quartz-enhanced multiheterodyne resonant photoacoustic spectroscopy. Light Sci. Appl. 2024 doi: 10.1038/s41377-024-01425-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Yin X., Dong L., Wu H., et al. Compact QEPAS humidity sensor in SF6 buffer gas for high-voltage gas power systems. Photoacoustics. 2022;25 doi: 10.1016/j.pacs.2021.100319. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Wei T., Zifarelli A., et al. High and flat spectral responsivity of quartz tuning fork used as infrared photodetector in tunable diode laser spectroscopy. Appl. Phys. Rev. 2021;8(4) [Google Scholar]
  • 20.Liu Y., Qiao S., Fang C., et al. A highly sensitive LITES sensor based on a multi-pass cell with dense spot pattern and a novel quartz tuning fork with low frequency. Opto-Electron. Adv. 2024;7(3) [Google Scholar]
  • 21.Qiao S., Ma Y., He Y., et al. Ppt level carbon monoxide detection based on light-induced thermoelastic spectroscopy exploring custom quartz tuning forks and a mid-infrared QCL. Opt. Express. 2021;29(16):25100. doi: 10.1364/OE.434128. [DOI] [PubMed] [Google Scholar]
  • 22.Hu Y., Qiao S., He Y., et al. Quartz-enhanced photoacoustic-photothermal spectroscopy for trace gas sensing. Opt. Express. 2021;29(4):5121–5127. doi: 10.1364/OE.418256. [DOI] [PubMed] [Google Scholar]
  • 23.Hu L., Zheng C., et al. Long-distance in-situ methane detection using near-infrared light-induced thermo-elastic spectroscopy. Photoacoustics. 2021;21 doi: 10.1016/j.pacs.2020.100230. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Zifarelli A., Sampaol A., et al. Methane and ethane detection from natural gas level down to trace concentrations using a compact mid-IR LITES sensor based on univariate calibration. Photoacoustics. 2023;29 doi: 10.1016/j.pacs.2023.100448. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Cheng Y., Xu Y., et al. Differential laser-induced thermoelastic spectroscopy for dual-gas CO2/CH4 detection. Measurement. 2024;240 [Google Scholar]
  • 26.Ma Y., Sui X., et al. Optical-domain modulation cancellation method for background-suppression and dual-gas detection in light-induced thermo-elastic spectroscopy. Sens. Actuators B-Chem. 2024;404 [Google Scholar]
  • 27.Zhang Q., Chang J., et al. Quartz tuning fork enhanced photothermal spectroscopy gas detection system with a novel QTF-self-difference technique. Sens. Actuators A-Phys. 2019;299 [Google Scholar]
  • 28.Xu L., Li J., Liu N., Zhou S. Quartz crystal tuning fork based 2f/1f wavelength modulation spectroscopy. Spectrochim. Acta A. 2022;267 doi: 10.1016/j.saa.2021.120608. [DOI] [PubMed] [Google Scholar]
  • 29.Ma Y., Hu Y., Qiao S. Trace gas sensing based on multi-quartz-enhanced photothermal spectroscopy. Photoacoustics. 2020;20 doi: 10.1016/j.pacs.2020.100206. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Wang Y., Cheng T., Lou C., et al. Carbon-based light-induced thermoelastic spectroscopy for ammonia gas sensing. Microw. Opt. Technol. Let. 2023;65(5):1086. [Google Scholar]
  • 31.Lou C., Wang Y., Huang L., et al. Quartz tuning fork (QTF) coating enhanced Mid-Infrared laser Induced-Thermoacoustic spectroscopy (LITES) for human exhaled methane detection. Infrared Phys. Technol. 2023;133 [Google Scholar]
  • 32.Dai J., Wang C., Liu P., et al. Sensitive light-induced thermoelastic spectroscopy-based oxygen sensor with a perovskite-modified quartz tuning fork. IEEE Sens. J. 2023;23(19):22380. [Google Scholar]
  • 33.Qiao S., Sampaolo A., Patimisco P. Ultra-highly sensitive HCl-LITES sensor based on a low-frequency quartz tuning fork and a fiber-coupled multi-pass cell. Photoacoustics. 2022;27 doi: 10.1016/j.pacs.2022.100381. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34.Xu L., Liu K., Liang J., et al. Micro-quartz crystal tuning fork-based photodetector array for trace gas detection. Anal. Chem. 2023;95(17):6955. doi: 10.1021/acs.analchem.3c00318. [DOI] [PubMed] [Google Scholar]
  • 35.Zheng H., Liu Y., Lin H., et al. Quartz-enhanced photoacoustic spectroscopy employing pilot line manufactured custom tuning forks. Photoacoustics. 2020;17 doi: 10.1016/j.pacs.2019.100158. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

Data will be made available on request.

Articles from Photoacoustics are provided here courtesy of Elsevier

RESOURCES