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Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser
Journal Pre-proofs Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser Qinduan Zhang, Jun Chang, Zhenhua Cong, Zongliang Wang PII: DOI: Reference:
S0263-2241(20)30138-X https://doi.org/10.1016/j.measurement.2020.107601 MEASUR 107601
To appear in:
Measurement
Received Date: Revised Date: Accepted Date:
4 July 2019 21 October 2019 9 February 2020
Please cite this article as: Q. Zhang, J. Chang, Z. Cong, Z. Wang, Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser, Measurement (2020), doi: https://doi.org/10.1016/j.measurement.2020.107601
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier Ltd.
Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser Qinduan Zhang,1,2 Jun Chang,1,* Zhenhua Cong,1 Zongliang Wang3 School of Information Science and Engineering and Shandong Provincial Key Laboratory of Laser Technology and
1
Application, Shandong University, Qingdao 266200, China Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique
2
de Louvain, Louvain-la-Neuve 1348, Belgium School of Physics Science and Information Technology and Shandong Key Laboratory of Optical Communication Science
3
and Technology, Liaocheng University, Liaocheng 252059, China *Corresponding author: [email protected]
Abstract: A long-path quartz tuning fork enhanced photothermal spectroscopy (QEPTS) gas sensor using a Q-switched fiber laser is proposed. A theoretical model is used to describe the process of the long-path QEPTS sensor and the factors that affect its performance. We can conclude that long optical path and high power are beneficial to the QEPTS sensor from the theoretical analysis. And we use our long-path QEPTS sensor for C2H2 detection at the wavelength of 1531.59 nm. With the scanning time of 4 s and the peak pulse power of 127.5 mW, an Allan deviation analysis shows that our sensor has a minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time and a good linear response (Rsquare = 0.99796). Key words: long-path, QEPTS, quartz tuning fork, Q-switched fiber laser, gas detection 1.
Introduction C2H2 is an inflammable gas formed during the combustion of hydrocarbon fuels. C2H2 monitoring is
indispensable for safety in chemical plants, gas power plants, and coal mines. Therefore, high sensitive C2H2 sensors have attracted wide attention [1-6]. And reports of different infrared absorption spectroscopy techniques for gases have increased rapidly in recent years. Photoacoustic spectroscopy [7-8], photothermal spectroscopy [9-10], and ring-down absorption spectroscopy [11], as well as intracavity absorption spectroscopy [12] were demonstrated to monitor gas concentrations. Intra-cavity fiber laser gas sensors have attracted considerable interest due to their several features: compact configuration, low noise and inherent fiber compatibility. Therefore, many researchers are devoted to the research of fiber laser in gas detection. One method is to utilize the laser generation process of the fiber laser for absorption path increase. The gas cell is directly placed within the laser cavity. In the process of laser generation, the laser passes through the gas absorption cell multiple times, which increases the efficient absorption path and improves the minimum detection limit (MDL). Plenty of research of this approach has been reported. Zhang et al. [13] proposed an intracavity sensor based on a linear cavity fiber laser for gas detection in 2004. Compared with the single pass path measurement sensor, the MDL of their sensor was enhanced 91 times. Liu et al. [14-15] applied the wavelength sweep technique (WST) to the intra-cavity fiber laser for trace gas detection. And the MDL could be limited less than 200 ppmv when this intra-cavity gas detection system was used for C2H2 detection. Stewart et al. [16] presented their progress on the investigation of intra-cavity gas detection system with the loop fiber lasers based on ring-down absorption spectroscopy. The results showed this method has a high MDL for near-infrared wavelength gas detection at the weak overtone absorption lines. Recently,
Krzempek et al [17] demonstrated the photothermal spectroscopy with a mode-locked ring cavity fiber laser for CO2 analysis. And their sensor achieved a MDL of 290 ppmv at the 1 s integration time and 10 ppmv at the 100 s integration time, respectively. Most recently, another method is to utilize the intra-cavity high power characteristics of fiber lasers. In photoacoustic spectroscopy, the PAS signal amplitude is linearly related to the laser power. So high power is beneficial to photoacoustic spectroscopy [18]. Wang et al. [19-20] proposed the fiber-ring laser intra-cavity photoacoustic spectroscopy gas sensor exploiting a fiber laser. The photoacoustic detection element was placed in the laser cavity to make full use of the intra-cavity laser power for gas detection. A minimum detectable C2H2 concentration of ppbv level was achieved. We also introduced an intracavity photoacoustic spectroscopy gas sensor with a Q-switched fiber laser in the past, the sensor achieved a MDL of 94.2 times than that of the conventional gas detection system measurement [21]. In 2018, a new technique called quartz tuning fork enhanced photothermal spectroscopy (QEPTS) was presented by Ma et al. [22-23], in which quartz tuning fork (QTF) was used as photothermal detection element. And their sensors achieved a MDL of ppbv level for C2H2 and CO detection. The experimental results showed that the QEPTS technique is a potential technique for gas detection. In this paper, we first presented a novel configuration of QEPTS gas sensor. Then, we investigated the influences of parameters on this sensor performance by the theoretical analysis. And we used this sensor to detect C2H2 at 1531.59 nm as a proof of principle. With the long optical path and high laser power, the sensor achieved a MDL of 6.1 ppbv and a good linear response (R-square = 0.99796) in concentration range from 200 ppmv to 996 ppmv. 2.
Fundamentals of QEPTS with a Q-switched fiber laser At room temperature and pressure, the transmission power of a laser beam through a uniform
absorbing gas can be descried by the well-known Beer-Lambert law [24].
I I 0 exp , 0 CL
(1)
Where α(ν, ν0) is the gas absorption coefficient at optical frequency ν. I(ν) and I0(ν) denote the measured transmitted laser power and the incident laser power, respectively. The term L is the length of absorption path. C is the concentration of gas to be measured. When α(ν, ν0)CL ≪ 1, the transmitted laser power could be expressed by:
I I 0 1 , 0 CL
(2)
The instantaneous output laser power P of the Q-switched fiber laser can be expressed as [25]:
P Sh
cT 2nD
(3)
c is speed of light in vacuum and h represents Planck constant. n is the refractive index of the active medium. D stands for the entire length of the resonant cavity. T is output coupler transmittance. S is the number of photons. It can be described as:
S N t ln
N N N in N in
(4)
ΔNin stands for population inversion in a Q-switched pulsed fiber laser at high Q state, ΔN and ΔNt are the intracavity population inversion and threshold population inversion, respectively. When ΔN = ΔNt, the peak pulse power is achieved. This condition is inserted into Equation (4), and S in Equation (3) is replaced by Equation (4), the peak pulse output power can be expressed as:
Ppeak h
cT N N N in N t ln 2nD N in
N cT N h N t in ln 1 2nD N in N
(5)
According to Equations (2) and (5), the transmitted laser intensity I(ν) can be expressed as:
I Ppeak 1 , 0 CL N in N cT 1 1 , 0 CL ln N t h N in 2nD N
(6)
The vibration amplitude of the cantilever tip due to the photothermal effect can be found from the following equation [26].
d1 d 2 l3 3 z 1 2 2 I d 2 K 1d1 2 d 2 H 4
(7)
The QTF is made by plating a Cr/Au thin layer on the surface of the quartz material. The subscripts 1 and 2 represent Cr/Au thin layer and quartz crystal material, respectively. where z is the deflection at the tip, σ1 and σ2 are the coefficients of thermal expansion for the two layers, l is the length of the QTF, d1 and d2 are the layer thicknesses, δ1 and δ2 are the thermal conductivities, H is the width of the QTF, and I is the power absorbed by the QTF. The vibration amplitude of the QTF can be described as: N in d d N l3 cT 3 1 1 , 0 CL ln N t h z 1 2 1 2 2 N in d 2 K 1d1 2 d 2 H 4 2nD N
(8) α is effective power conversion coefficient. So the current generated by piezoelectric effect of QTF can be expressed as:
N d d N l3 cT 3 N t in ln 1 1 , 0 CL i z 1 2 1 2 2 h N in d 2 K 1d1 2 d 2 H 4 2nD N (9) 3 d1 d 2 l 3 P 1 , 0 CL = 1 2 2 d 2 K 1d1 2 d 2 H 4 Here β defines the piezoelectric coefficient of quartz crystal material. As can be seen from Equation (9), the laser power P and the optical path L are directly proportional to the piezoelectric current (QEPTS signal). 3.
Experimental configuration
980 nm pump laser
Circulator WDM
QTF
EDF
Gas cell
Fiber Collimator
Preamplifier
FBG 20:80 Coupler
PZT Driver AOM
Lock-in amplifier
PZT Actuator
Signal generator
Computer
Fig. 1 Schematic of the long-path QEPTS gas sensor. QTF, quartz tuning fork; EDF, erbium doped fiber; AOM, acousto-optic modulator; PZT, piezoelectric transducer; WDM, wavelength division multiplexer; FBG, fiber Bragg grating. The system setup of long-path QEPTS gas sensor is shown in Fig. 1. A 1500 parts per million (ppm), erbium doped fiber (EDF) (EDFC-980-HP, Nufern, East Granby, CT, America) with a length of 15 m is pumped by a 980 nm pump laser (650 mW) (VLSS-976-B-650-1, Hanyu, Shanghai, China) via a 980/1550 fiber wavelength division multiplexing (WDM). A fiber Bragg grating (FBG) with a central wavelength of 1531.59 nm (Corresponding to gas absorption peak of C2H2) [27] and a bandwidth of 100 pm is used as wavelength selector. A circulator couples the FBG into the laser cavity. A gas absorption cell with a 30 cm absorption path is placed in the fiber laser cavity, the laser passes through the absorption cell repeatedly, leading an increase in the absorption path. Piezoelectric transducer (PZT) driver (PX200, PiezoDrive, Shortland, Australia) and PZT actuator (SA070742, PiezoDrive, Shortland, Australia) are used to drive the PZT actuator and stretch the FBG periodically, respectively. The acousto-optic modulator (AOM) (T-M200-0.1C2J-3-F2P, Gooch&Housego, Ilminster, UK) is used as the laser intensity modulator. The signal generator (FY2300A, Feel Tech, Zhengzhou, China) provides modulation signals to the PZT driver and the AOM. The modulation frequency of the modulation signal is 32.715 kHz (see Fig. 2 (a), the response frequency curve of the QTF was measured by photothermal effect), which is consistent with resonant frequency of QTF. 80% port of the 20:80 fiber coupler is implemented to make the laser which reflected by the FBG into the laser cavity. The laser output from the 20% port incident on the QTF surface. A small size collimator is used to output the laser, and the diagram of the laser spot incidents on the QTF is shown in Fig. 2(b). Its diameter (0.103 mm) is smaller than the width of QTF (0.6 mm). The piezoelectric current signals caused by the QTF vibration are converted into voltage signals by a preamplifier (CA3140E, Intersil, Milpitas, CA, USA) circuit. And the preamplifier circuit has a gain of 10 MΩ. Then the voltage signals are demodulated by a lock-in amplifier (Model 7230, AMETEK, Berwyn, PA, USA) and monitored by an oscilloscope.
(a)
(b)
QTF signal (a.u.)
32.715 kHz
103 um
32.55
32.60
32.65
32.70
32.75
32.80
32.85
Frequency (kHz)
Fig. 2 (a) Frequency response curve of the QTF is measured by photothermal effect. (b) The laser spot of the output laser from the fiber collimator. 4.
Experimental results and discussions As shown in Fig. 3(a), a sinusoidal wave with a scanning time of 4 s is used as the driving signal to
stretch the FBG. The tuning characteristics of the wavelength and the laser power output from the 20% port of the 20:80 fiber coupler is shown in Fig. 3(b), measured by adjusting the PZT driving voltage from 5.6 V to 77.6 V. This PZT driving range allows to contain the laser wavelength across the C2H2 absorption line. Under this driving voltage range, the output peak pulse power is approximately 127.5 mW as shown in Fig. 3(b). Fig. 3(c) depicts the output spectrum of the fiber laser when the PZT driving voltage is 28.4 V, corresponding to the gas absorption line of C2H2 at 1531.59 nm. Fig. 3 (d) shows the laser pulse sequence diagram. The modulation frequency of the laser pulse is equal to the resonance frequency of the QTF.
Laser wavelength (nm)
PZT voltage (V)
70 60 50 40 30 20 10 0 0.0
(b)
77.6 V
5.6 V
0.5
1.0
1.5
2.0
2.5
1531.8
3.5
127.0
1531.7
126.5
1531.6
126.0
1531.5 1531.4
3.0
127.5
4.0
Laser wavelength Output laser power 0
10
20
50
60
70
125.0 80
80
100
(d)
(c) c =1531.59 nm
Laser power (a.u.)
Laser intensity (a.u.)
40
PZT voltage (V)
Time (s)
1520
30
125.5
Output laser power (mW)
1531.9
80 (a)
PZT voltage=28.4 V
1524
1528
1532
Wavelength (nm)
1536
1540
32.715 kHz
0
20
40
60
Time (s )
Fig. 3 (a) The PZT driving voltage. (b) Tuning characteristics of the output laser power and laser
wavelength with different PZT driving voltage ranging from 5.6 V to 77.6 V. (c) Output spectrum with the PZT driving voltage of 28.4 V. (d) The laser pulse sequence diagram at modulation frequency of 32.715 kHz.
700
QEPTS signal (mV)
600 500 400 300 200 100 0
0
2
4
6
8
10
12
14
16
Scanning time (s) Fig. 4 Measured QEPTS signals at different scanning time. To obtain the optimum QEPTS signal amplitude, QEPTS signal was measured in different scanning periods by adjusting the scanning time of the PZT driver. The measurement was performed at the room temperature and pressure. The 996 ppmv C2H2 sample was produced by a gas distribution system. The measurement result is shown in Fig. 4. And it could be concluded that the QEPTS signals increase with the scanning times, and when the scanning time is more than 4 s, the QEPTS signal achieves the maximum value. So the scanning time was set to 4 s to maximize the QEPTS signal and ensure real-time detection. 6.0 5.8
100
(a)
Allan deviation (ppbv)
QEPTS Signal (V)
5.6 5.4 5.2 5.0 4.8
647 mV
4.6 4.4 4.2 4.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Time (s)
(b)
10 6.1
1
10
48
100
1000
Integration time (s)
Fig. 5 (a) The representative QEPTS signal of 996 ppmv concentration of C2H2. (b) Allan deviation analysis in ppbv for the long-path QEPTS gas sensor. Preliminary measurements of the long-path QEPTS gas sensor response to 996 ppmv C2H2 concentration (Fig. 5(a)) was measured at the absorption wavelength of 1531.59 nm. To evaluate the accuracy and long-term stability of the long-path QEPTS C2H2 sensor, an Allan deviation analysis was calculated when pure N2 was injected into the long-path QEPTS C2H2 sensor. Fig. 5(b) shows the Allan deviation analysis chart, the MDL of the long-path QEPTS gas sensor for C2H2 detection is 6.1 ppbv at the optimum integration time of 48 s. So our sensor has better MDL than other QEPTS C2H2 sensors [22]. And the measurement results indicate that the long-path QEPTS gas sensor has high stability and
sensitivity.
700
QEPTS signal (mV)
600
y=0.656x-6.6 R-Square=0.99796
500 400 300 200 100 0
0
200
400
600
800
1000
C2H2 concentration (ppmv) Fig. 6 The relation between the QEPTS signal amplitude and C2H2 concentration, each data point is the average of multiple measurements at the same concentration, at the room temperature and pressure of 1 bar. Finally, the C2H2 with a concentration range from 200 ppmv to 996 ppmv which produced by a gas distribution system was injected to the gas absorption cell to demonstrate the linear response of the long-path QEPTS sensor. The linear response of the long-path QEPTS gas sensor for various C2H2 concentrations is illustrated in Fig. 6. The R-square value represents the agreement between the measured data points and fitting curve, is equal to 0.99796 in this sensor system. This result shows that the long-path QEPTS sensor has a good linearity response to monitor C2H2 concentration. 5.
Conclusion In conclusion, a long-path QEPTS gas sensor using a high power Q-switched fiber laser was proposed
and experimentally demonstrated. By applying optimum scanning time, the MDL can be increased to 6.1 ppbv at the integration time of 48 s. The experimental results demonstrate a good linearity and the R-square is 0.99796. And this long-length QEPTS gas sensor has many merits, such as safety in flammable and explosive environments, the capability of long distance sensing, anti-electromagnetic interference capability, and high sensitivity. Further improvement of the system structure will be made the long-path QEPTS gas sensor more compact and miniaturized in order to make it more suitable for the actual measurement process. Funding This work was supported by National Natural Science Foundation of China (61475085), and the China Scholarship Council (201906220092). References [1] B. Bernhardt, A. Ozawa, P. Jacquet, M. Jacquey, Y. Kobayashi, T. Udem, R. Holzwarth, G. Guelachvili, T.W. Haensch, N. Picque, Cavity-enhanced dual-comb spectroscopy, NAT PHOTONICS, 4 (2010) 55-57. [2] Q. Wang, Z. Wang, J. Chang, W. Ren, Fiber-ring laser-based intracavity photoacoustic spectroscopy for trace gas sensing, OPT LETT, 42 (2017) 2114-2117. [3] Y. Ma, S. Qiao, Y. He, Y. Li, Z. Zhang, X. Yu, F.K. Tittel, Highly sensitive acetylene detection based on multi-pass retro-reflection-cavity-enhanced photoacoustic spectroscopy and a fiber amplified diode
laser, OPT EXPRESS, 27 (2019) 14163-14172. [4] J. Jiang, Z. Wang, X. Han, C. Zhang, G. Ma, C. Li, Y. Luo, Multi-Gas Detection in Power Transformer Oil Based on Tunable Diode Laser Absorption Spectrum, IEEE T DIELECT EL IN, 26 (2019) 153-161. [5] L. Dong, A.A. Kosterev, D. Thomazy, F.K. Tittel, QEPAS spectrophones: design, optimization, and performance, APPL PHYS B-LASERS O, 100 (2010) 627-635. [6] J. Li, W. Chen, B. Yu, Recent Progress on Infrared Photoacoustic Spectroscopy Techniques, APPL SPECTROSC REV, 46 (2011) 440-471. [7] H. Wu, X. Yin, L. Dong, K. Pei, A. Sampaolo, P. Patimisco, H. Zheng, W. Ma, L. Zhang, W. Yin, L. Xiao, V. Spagnolo, S. Jia, F.K. Tittel, Simultaneous dual-gas QEPAS detection based on a fundamental and overtone combined vibration of quartz tuning fork, APPL PHYS LETT, 110 (2017). [8] H. Wu, L. Dong, H. Zheng, Y. Yu, W. Ma, L. Zhang, W. Yin, L. Xiao, S. Jia, F.K. Tittel, Beat frequency quartz-enhanced photoacoustic spectroscopy for fast and calibration-free continuous trace-gas monitoring, NAT COMMUN, 8 (2017). [9] W. Jin, Y. Cao, F. Yang, H.L. Ho, Ultra-sensitive all-fibre photothermal spectroscopy with large dynamic range, NAT COMMUN, 6 (2015). [10] F. Yang, Y. Tan, W. Jin, Y. Lin, Y. Qi, H.L. Ho, Hollow-core fiber Fabry-Perot photothermal gas sensor, OPT LETT, 41 (2016) 3025-3028. [11] G. Stewart, G. Whitenett, K. Vijayraghavan, S. Sridaran, Investigation of the dynamic response of erbium fiber lasers with potential application for sensors, J LIGHTWAVE TECHNOL, 25 (2007) 1786-1796. [12] H. Zhang, K. Liu, D. Jia, T. Xu, T. Liu, G. Peng, W. Jing, Y. Zhang, Improved low concentration gas detection system based on intracavity fiber laser, REV SCI INSTRUM, 82 (2011). [13] Y. Zhang, M. Zhang, W. Jin, H.L. Ho, M.S. Demokan, B. Culshaw, G. Stewart, Investigation of erbiumdoped fiber laser intra-cavity absorption sensor for gas detection, OPT COMMUN, 232 (2004) 295-301. [14] K. Liu, W. Jing, G. Peng, J. Zhang, Y. Wang, T. Liu, D. Jia, H. Zhang, Y. Zhang, Wavelength Sweep of Intracavity Fiber Laser for Low Concentration Gas Detection, IEEE PHOTONIC TECH L, 20 (2008) 15151517. [15] K. Liu, T. Liu, J. Jiang, G. Peng, H. Zhang, D. Jia, Y. Wang, W. Jing, Y. Zhang, Investigation of Wavelength Modulation and Wavelength Sweep Techniques in Intracavity Fiber Laser for Gas Detection, J LIGHTWAVE TECHNOL, 29 (2011) 15-21. [16] G. Stewart, P. Shields, B. Culshaw, Development of fibre laser systems for ring-down and intracavity gas spectroscopy in the near-IR, MEAS SCI TECHNOL, 15 (2004) 1621-1628. [17] K. Krzempek, G. Dudzik, K. Abramski, Photothermal spectroscopy of CO2 in an intracavity modelocked fiber laser configuration, OPT EXPRESS, 26 (2018) 28861-28871. [18] Y. Ma, Y. He, L. Zhang, X. Yu, J. Zhang, R. Sun, F.K. Tittel, Ultra-high sensitive acetylene detection using quartz-enhanced photoacoustic spectroscopy with a fiber amplified diode laser and a 30.72 kHz quartz tuning fork, APPL PHYS LETT, 110 (2017). [19] Q. Wang, Z. Wang, W. Ren, Theoretical and Experimental Investigation of Fiber-Ring Laser Intracavity Photoacoustic Spectroscopy (FLI-PAS) for Acetylene Detection, J LIGHTWAVE TECHNOL, 35 (2017) 4519-4525. [20] Q. Wang, Z. Wang, W. Ren, P. Patimisco, A. Sampaolo, V. Spagnolo, Fiber-ring laser intracavity QEPAS gas sensor using a 7.2 kHz quartz tuning fork, SENSOR ACTUAT B-CHEM, 268 (2018) 512-518. [21] Q. Zhang, J. Chang, Q. Wang, Z. Wang, F. Wang, Z. Qin, Acousto-Optic Q-Switched Fiber Laser-Based Intra-Cavity Photoacoustic Spectroscopy for Trace Gas Detection, SENSORS-BASEL, 18 (2018). [22] Y. Ma, Y. He, Y. Tong, X. Yu, F.K. Tittel, Quartz-tuning-fork enhanced photothermal spectroscopy
for ultra-high sensitive trace gas detection, OPT EXPRESS, 26 (2018) 32103-32110. [23] Y. He, Y. Ma, Y. Tong, X. Yu, F.K. Tittel, Ultra-high sensitive light-induced thermoelastic spectroscopy sensor with a high Q-factor quartz tuning fork and a multipass cell, OPT LETT, 44 (2019) 1904-1907. [24] Z. Wu, Y. Zhang, H. Zhang, N. Gai, A photoacoustic spectroscopy measurement of near-infrared low-mass multi-component gas at room temperature and atmospheric pressure, MEASUREMENT, 139 (2019) 411-420. [25] C.J. Gaeta, M. Digonnet, H.J. Shaw, Pulse characteristics of Q-switched fiber lasers, J LIGHTWAVE TECHNOL, 5 (1987) 1645-1651. [26] C.W. Van Neste, L.R. Senesac, D. Yi, T. Thundat, Standoff detection of explosive residues using photothermal microcantilevers, APPL PHYS LETT, 92 (2008). [27] I.E. Gordon, L.S. Rothman, C. Hill, R.V. Kochanov, Y. Tan, P.F. Bernath, M. Birk, V. Boudon, A. Campargue, K.V. Chance, B.J. Drouin, J.M. Flaud, R.R. Gamache, J.T. Hodges, D. Jacquemart, V.I. Perevalov, A. Perrin, K.P. Shine, M.A.H. Smith, J. Tennyson, G.C. Toon, H. Tran, V.G. Tyuterev, A. Barbe, A.G. Csaszar, V.M. Devi, T. Furtenbacher, J.J. Harrison, J.M. Hartmann, A. Jolly, T.J. Johnson, T. Karman, I. Kleiner, A.A. Kyuberis, J. Loos, O.M. Lyulin, S.T. Massie, S.N. Mikhailenko, N. Moazzen-Ahmadi, H.S.P. Mueller, O.V. Naumenko, A.V. Nikitin, O.L. Polyansky, M. Rey, M. Rotger, S.W. Sharpe, K. Sung, E. Starikova, S.A. Tashkun, J. Vander Auwera, G. Wagner, J. Wilzewski, P. Wcislo, S. Yu, E.J. Zak, The HITRAN2016 molecular spectroscopic database, J QUANT SPECTROSC RA, 203 (2017) 3-69.
Highlights 1. A long-path QEPTS gas sensor using a high power Q-switched fiber laser was proposed. 2. Long optical path and high power are beneficial to the QEPTS sensor. 3. A minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time was achieved.
Declaration of Interest Statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser”
Jun Chang
S0263-2241(20)30138-X https://doi.org/10.1016/j.measurement.2020.107601 MEASUR 107601
To appear in:
Measurement
Received Date: Revised Date: Accepted Date:
4 July 2019 21 October 2019 9 February 2020
Please cite this article as: Q. Zhang, J. Chang, Z. Cong, Z. Wang, Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser, Measurement (2020), doi: https://doi.org/10.1016/j.measurement.2020.107601
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier Ltd.
Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser Qinduan Zhang,1,2 Jun Chang,1,* Zhenhua Cong,1 Zongliang Wang3 School of Information Science and Engineering and Shandong Provincial Key Laboratory of Laser Technology and
1
Application, Shandong University, Qingdao 266200, China Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique
2
de Louvain, Louvain-la-Neuve 1348, Belgium School of Physics Science and Information Technology and Shandong Key Laboratory of Optical Communication Science
3
and Technology, Liaocheng University, Liaocheng 252059, China *Corresponding author: [email protected]
Abstract: A long-path quartz tuning fork enhanced photothermal spectroscopy (QEPTS) gas sensor using a Q-switched fiber laser is proposed. A theoretical model is used to describe the process of the long-path QEPTS sensor and the factors that affect its performance. We can conclude that long optical path and high power are beneficial to the QEPTS sensor from the theoretical analysis. And we use our long-path QEPTS sensor for C2H2 detection at the wavelength of 1531.59 nm. With the scanning time of 4 s and the peak pulse power of 127.5 mW, an Allan deviation analysis shows that our sensor has a minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time and a good linear response (Rsquare = 0.99796). Key words: long-path, QEPTS, quartz tuning fork, Q-switched fiber laser, gas detection 1.
Introduction C2H2 is an inflammable gas formed during the combustion of hydrocarbon fuels. C2H2 monitoring is
indispensable for safety in chemical plants, gas power plants, and coal mines. Therefore, high sensitive C2H2 sensors have attracted wide attention [1-6]. And reports of different infrared absorption spectroscopy techniques for gases have increased rapidly in recent years. Photoacoustic spectroscopy [7-8], photothermal spectroscopy [9-10], and ring-down absorption spectroscopy [11], as well as intracavity absorption spectroscopy [12] were demonstrated to monitor gas concentrations. Intra-cavity fiber laser gas sensors have attracted considerable interest due to their several features: compact configuration, low noise and inherent fiber compatibility. Therefore, many researchers are devoted to the research of fiber laser in gas detection. One method is to utilize the laser generation process of the fiber laser for absorption path increase. The gas cell is directly placed within the laser cavity. In the process of laser generation, the laser passes through the gas absorption cell multiple times, which increases the efficient absorption path and improves the minimum detection limit (MDL). Plenty of research of this approach has been reported. Zhang et al. [13] proposed an intracavity sensor based on a linear cavity fiber laser for gas detection in 2004. Compared with the single pass path measurement sensor, the MDL of their sensor was enhanced 91 times. Liu et al. [14-15] applied the wavelength sweep technique (WST) to the intra-cavity fiber laser for trace gas detection. And the MDL could be limited less than 200 ppmv when this intra-cavity gas detection system was used for C2H2 detection. Stewart et al. [16] presented their progress on the investigation of intra-cavity gas detection system with the loop fiber lasers based on ring-down absorption spectroscopy. The results showed this method has a high MDL for near-infrared wavelength gas detection at the weak overtone absorption lines. Recently,
Krzempek et al [17] demonstrated the photothermal spectroscopy with a mode-locked ring cavity fiber laser for CO2 analysis. And their sensor achieved a MDL of 290 ppmv at the 1 s integration time and 10 ppmv at the 100 s integration time, respectively. Most recently, another method is to utilize the intra-cavity high power characteristics of fiber lasers. In photoacoustic spectroscopy, the PAS signal amplitude is linearly related to the laser power. So high power is beneficial to photoacoustic spectroscopy [18]. Wang et al. [19-20] proposed the fiber-ring laser intra-cavity photoacoustic spectroscopy gas sensor exploiting a fiber laser. The photoacoustic detection element was placed in the laser cavity to make full use of the intra-cavity laser power for gas detection. A minimum detectable C2H2 concentration of ppbv level was achieved. We also introduced an intracavity photoacoustic spectroscopy gas sensor with a Q-switched fiber laser in the past, the sensor achieved a MDL of 94.2 times than that of the conventional gas detection system measurement [21]. In 2018, a new technique called quartz tuning fork enhanced photothermal spectroscopy (QEPTS) was presented by Ma et al. [22-23], in which quartz tuning fork (QTF) was used as photothermal detection element. And their sensors achieved a MDL of ppbv level for C2H2 and CO detection. The experimental results showed that the QEPTS technique is a potential technique for gas detection. In this paper, we first presented a novel configuration of QEPTS gas sensor. Then, we investigated the influences of parameters on this sensor performance by the theoretical analysis. And we used this sensor to detect C2H2 at 1531.59 nm as a proof of principle. With the long optical path and high laser power, the sensor achieved a MDL of 6.1 ppbv and a good linear response (R-square = 0.99796) in concentration range from 200 ppmv to 996 ppmv. 2.
Fundamentals of QEPTS with a Q-switched fiber laser At room temperature and pressure, the transmission power of a laser beam through a uniform
absorbing gas can be descried by the well-known Beer-Lambert law [24].
I I 0 exp , 0 CL
(1)
Where α(ν, ν0) is the gas absorption coefficient at optical frequency ν. I(ν) and I0(ν) denote the measured transmitted laser power and the incident laser power, respectively. The term L is the length of absorption path. C is the concentration of gas to be measured. When α(ν, ν0)CL ≪ 1, the transmitted laser power could be expressed by:
I I 0 1 , 0 CL
(2)
The instantaneous output laser power P of the Q-switched fiber laser can be expressed as [25]:
P Sh
cT 2nD
(3)
c is speed of light in vacuum and h represents Planck constant. n is the refractive index of the active medium. D stands for the entire length of the resonant cavity. T is output coupler transmittance. S is the number of photons. It can be described as:
S N t ln
N N N in N in
(4)
ΔNin stands for population inversion in a Q-switched pulsed fiber laser at high Q state, ΔN and ΔNt are the intracavity population inversion and threshold population inversion, respectively. When ΔN = ΔNt, the peak pulse power is achieved. This condition is inserted into Equation (4), and S in Equation (3) is replaced by Equation (4), the peak pulse output power can be expressed as:
Ppeak h
cT N N N in N t ln 2nD N in
N cT N h N t in ln 1 2nD N in N
(5)
According to Equations (2) and (5), the transmitted laser intensity I(ν) can be expressed as:
I Ppeak 1 , 0 CL N in N cT 1 1 , 0 CL ln N t h N in 2nD N
(6)
The vibration amplitude of the cantilever tip due to the photothermal effect can be found from the following equation [26].
d1 d 2 l3 3 z 1 2 2 I d 2 K 1d1 2 d 2 H 4
(7)
The QTF is made by plating a Cr/Au thin layer on the surface of the quartz material. The subscripts 1 and 2 represent Cr/Au thin layer and quartz crystal material, respectively. where z is the deflection at the tip, σ1 and σ2 are the coefficients of thermal expansion for the two layers, l is the length of the QTF, d1 and d2 are the layer thicknesses, δ1 and δ2 are the thermal conductivities, H is the width of the QTF, and I is the power absorbed by the QTF. The vibration amplitude of the QTF can be described as: N in d d N l3 cT 3 1 1 , 0 CL ln N t h z 1 2 1 2 2 N in d 2 K 1d1 2 d 2 H 4 2nD N
(8) α is effective power conversion coefficient. So the current generated by piezoelectric effect of QTF can be expressed as:
N d d N l3 cT 3 N t in ln 1 1 , 0 CL i z 1 2 1 2 2 h N in d 2 K 1d1 2 d 2 H 4 2nD N (9) 3 d1 d 2 l 3 P 1 , 0 CL = 1 2 2 d 2 K 1d1 2 d 2 H 4 Here β defines the piezoelectric coefficient of quartz crystal material. As can be seen from Equation (9), the laser power P and the optical path L are directly proportional to the piezoelectric current (QEPTS signal). 3.
Experimental configuration
980 nm pump laser
Circulator WDM
QTF
EDF
Gas cell
Fiber Collimator
Preamplifier
FBG 20:80 Coupler
PZT Driver AOM
Lock-in amplifier
PZT Actuator
Signal generator
Computer
Fig. 1 Schematic of the long-path QEPTS gas sensor. QTF, quartz tuning fork; EDF, erbium doped fiber; AOM, acousto-optic modulator; PZT, piezoelectric transducer; WDM, wavelength division multiplexer; FBG, fiber Bragg grating. The system setup of long-path QEPTS gas sensor is shown in Fig. 1. A 1500 parts per million (ppm), erbium doped fiber (EDF) (EDFC-980-HP, Nufern, East Granby, CT, America) with a length of 15 m is pumped by a 980 nm pump laser (650 mW) (VLSS-976-B-650-1, Hanyu, Shanghai, China) via a 980/1550 fiber wavelength division multiplexing (WDM). A fiber Bragg grating (FBG) with a central wavelength of 1531.59 nm (Corresponding to gas absorption peak of C2H2) [27] and a bandwidth of 100 pm is used as wavelength selector. A circulator couples the FBG into the laser cavity. A gas absorption cell with a 30 cm absorption path is placed in the fiber laser cavity, the laser passes through the absorption cell repeatedly, leading an increase in the absorption path. Piezoelectric transducer (PZT) driver (PX200, PiezoDrive, Shortland, Australia) and PZT actuator (SA070742, PiezoDrive, Shortland, Australia) are used to drive the PZT actuator and stretch the FBG periodically, respectively. The acousto-optic modulator (AOM) (T-M200-0.1C2J-3-F2P, Gooch&Housego, Ilminster, UK) is used as the laser intensity modulator. The signal generator (FY2300A, Feel Tech, Zhengzhou, China) provides modulation signals to the PZT driver and the AOM. The modulation frequency of the modulation signal is 32.715 kHz (see Fig. 2 (a), the response frequency curve of the QTF was measured by photothermal effect), which is consistent with resonant frequency of QTF. 80% port of the 20:80 fiber coupler is implemented to make the laser which reflected by the FBG into the laser cavity. The laser output from the 20% port incident on the QTF surface. A small size collimator is used to output the laser, and the diagram of the laser spot incidents on the QTF is shown in Fig. 2(b). Its diameter (0.103 mm) is smaller than the width of QTF (0.6 mm). The piezoelectric current signals caused by the QTF vibration are converted into voltage signals by a preamplifier (CA3140E, Intersil, Milpitas, CA, USA) circuit. And the preamplifier circuit has a gain of 10 MΩ. Then the voltage signals are demodulated by a lock-in amplifier (Model 7230, AMETEK, Berwyn, PA, USA) and monitored by an oscilloscope.
(a)
(b)
QTF signal (a.u.)
32.715 kHz
103 um
32.55
32.60
32.65
32.70
32.75
32.80
32.85
Frequency (kHz)
Fig. 2 (a) Frequency response curve of the QTF is measured by photothermal effect. (b) The laser spot of the output laser from the fiber collimator. 4.
Experimental results and discussions As shown in Fig. 3(a), a sinusoidal wave with a scanning time of 4 s is used as the driving signal to
stretch the FBG. The tuning characteristics of the wavelength and the laser power output from the 20% port of the 20:80 fiber coupler is shown in Fig. 3(b), measured by adjusting the PZT driving voltage from 5.6 V to 77.6 V. This PZT driving range allows to contain the laser wavelength across the C2H2 absorption line. Under this driving voltage range, the output peak pulse power is approximately 127.5 mW as shown in Fig. 3(b). Fig. 3(c) depicts the output spectrum of the fiber laser when the PZT driving voltage is 28.4 V, corresponding to the gas absorption line of C2H2 at 1531.59 nm. Fig. 3 (d) shows the laser pulse sequence diagram. The modulation frequency of the laser pulse is equal to the resonance frequency of the QTF.
Laser wavelength (nm)
PZT voltage (V)
70 60 50 40 30 20 10 0 0.0
(b)
77.6 V
5.6 V
0.5
1.0
1.5
2.0
2.5
1531.8
3.5
127.0
1531.7
126.5
1531.6
126.0
1531.5 1531.4
3.0
127.5
4.0
Laser wavelength Output laser power 0
10
20
50
60
70
125.0 80
80
100
(d)
(c) c =1531.59 nm
Laser power (a.u.)
Laser intensity (a.u.)
40
PZT voltage (V)
Time (s)
1520
30
125.5
Output laser power (mW)
1531.9
80 (a)
PZT voltage=28.4 V
1524
1528
1532
Wavelength (nm)
1536
1540
32.715 kHz
0
20
40
60
Time (s )
Fig. 3 (a) The PZT driving voltage. (b) Tuning characteristics of the output laser power and laser
wavelength with different PZT driving voltage ranging from 5.6 V to 77.6 V. (c) Output spectrum with the PZT driving voltage of 28.4 V. (d) The laser pulse sequence diagram at modulation frequency of 32.715 kHz.
700
QEPTS signal (mV)
600 500 400 300 200 100 0
0
2
4
6
8
10
12
14
16
Scanning time (s) Fig. 4 Measured QEPTS signals at different scanning time. To obtain the optimum QEPTS signal amplitude, QEPTS signal was measured in different scanning periods by adjusting the scanning time of the PZT driver. The measurement was performed at the room temperature and pressure. The 996 ppmv C2H2 sample was produced by a gas distribution system. The measurement result is shown in Fig. 4. And it could be concluded that the QEPTS signals increase with the scanning times, and when the scanning time is more than 4 s, the QEPTS signal achieves the maximum value. So the scanning time was set to 4 s to maximize the QEPTS signal and ensure real-time detection. 6.0 5.8
100
(a)
Allan deviation (ppbv)
QEPTS Signal (V)
5.6 5.4 5.2 5.0 4.8
647 mV
4.6 4.4 4.2 4.0 0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Time (s)
(b)
10 6.1
1
10
48
100
1000
Integration time (s)
Fig. 5 (a) The representative QEPTS signal of 996 ppmv concentration of C2H2. (b) Allan deviation analysis in ppbv for the long-path QEPTS gas sensor. Preliminary measurements of the long-path QEPTS gas sensor response to 996 ppmv C2H2 concentration (Fig. 5(a)) was measured at the absorption wavelength of 1531.59 nm. To evaluate the accuracy and long-term stability of the long-path QEPTS C2H2 sensor, an Allan deviation analysis was calculated when pure N2 was injected into the long-path QEPTS C2H2 sensor. Fig. 5(b) shows the Allan deviation analysis chart, the MDL of the long-path QEPTS gas sensor for C2H2 detection is 6.1 ppbv at the optimum integration time of 48 s. So our sensor has better MDL than other QEPTS C2H2 sensors [22]. And the measurement results indicate that the long-path QEPTS gas sensor has high stability and
sensitivity.
700
QEPTS signal (mV)
600
y=0.656x-6.6 R-Square=0.99796
500 400 300 200 100 0
0
200
400
600
800
1000
C2H2 concentration (ppmv) Fig. 6 The relation between the QEPTS signal amplitude and C2H2 concentration, each data point is the average of multiple measurements at the same concentration, at the room temperature and pressure of 1 bar. Finally, the C2H2 with a concentration range from 200 ppmv to 996 ppmv which produced by a gas distribution system was injected to the gas absorption cell to demonstrate the linear response of the long-path QEPTS sensor. The linear response of the long-path QEPTS gas sensor for various C2H2 concentrations is illustrated in Fig. 6. The R-square value represents the agreement between the measured data points and fitting curve, is equal to 0.99796 in this sensor system. This result shows that the long-path QEPTS sensor has a good linearity response to monitor C2H2 concentration. 5.
Conclusion In conclusion, a long-path QEPTS gas sensor using a high power Q-switched fiber laser was proposed
and experimentally demonstrated. By applying optimum scanning time, the MDL can be increased to 6.1 ppbv at the integration time of 48 s. The experimental results demonstrate a good linearity and the R-square is 0.99796. And this long-length QEPTS gas sensor has many merits, such as safety in flammable and explosive environments, the capability of long distance sensing, anti-electromagnetic interference capability, and high sensitivity. Further improvement of the system structure will be made the long-path QEPTS gas sensor more compact and miniaturized in order to make it more suitable for the actual measurement process. Funding This work was supported by National Natural Science Foundation of China (61475085), and the China Scholarship Council (201906220092). References [1] B. Bernhardt, A. Ozawa, P. Jacquet, M. Jacquey, Y. Kobayashi, T. Udem, R. Holzwarth, G. Guelachvili, T.W. Haensch, N. Picque, Cavity-enhanced dual-comb spectroscopy, NAT PHOTONICS, 4 (2010) 55-57. [2] Q. Wang, Z. Wang, J. Chang, W. Ren, Fiber-ring laser-based intracavity photoacoustic spectroscopy for trace gas sensing, OPT LETT, 42 (2017) 2114-2117. [3] Y. Ma, S. Qiao, Y. He, Y. Li, Z. Zhang, X. Yu, F.K. Tittel, Highly sensitive acetylene detection based on multi-pass retro-reflection-cavity-enhanced photoacoustic spectroscopy and a fiber amplified diode
laser, OPT EXPRESS, 27 (2019) 14163-14172. [4] J. Jiang, Z. Wang, X. Han, C. Zhang, G. Ma, C. Li, Y. Luo, Multi-Gas Detection in Power Transformer Oil Based on Tunable Diode Laser Absorption Spectrum, IEEE T DIELECT EL IN, 26 (2019) 153-161. [5] L. Dong, A.A. Kosterev, D. Thomazy, F.K. Tittel, QEPAS spectrophones: design, optimization, and performance, APPL PHYS B-LASERS O, 100 (2010) 627-635. [6] J. Li, W. Chen, B. Yu, Recent Progress on Infrared Photoacoustic Spectroscopy Techniques, APPL SPECTROSC REV, 46 (2011) 440-471. [7] H. Wu, X. Yin, L. Dong, K. Pei, A. Sampaolo, P. Patimisco, H. Zheng, W. Ma, L. Zhang, W. Yin, L. Xiao, V. Spagnolo, S. Jia, F.K. Tittel, Simultaneous dual-gas QEPAS detection based on a fundamental and overtone combined vibration of quartz tuning fork, APPL PHYS LETT, 110 (2017). [8] H. Wu, L. Dong, H. Zheng, Y. Yu, W. Ma, L. Zhang, W. Yin, L. Xiao, S. Jia, F.K. Tittel, Beat frequency quartz-enhanced photoacoustic spectroscopy for fast and calibration-free continuous trace-gas monitoring, NAT COMMUN, 8 (2017). [9] W. Jin, Y. Cao, F. Yang, H.L. Ho, Ultra-sensitive all-fibre photothermal spectroscopy with large dynamic range, NAT COMMUN, 6 (2015). [10] F. Yang, Y. Tan, W. Jin, Y. Lin, Y. Qi, H.L. Ho, Hollow-core fiber Fabry-Perot photothermal gas sensor, OPT LETT, 41 (2016) 3025-3028. [11] G. Stewart, G. Whitenett, K. Vijayraghavan, S. Sridaran, Investigation of the dynamic response of erbium fiber lasers with potential application for sensors, J LIGHTWAVE TECHNOL, 25 (2007) 1786-1796. [12] H. Zhang, K. Liu, D. Jia, T. Xu, T. Liu, G. Peng, W. Jing, Y. Zhang, Improved low concentration gas detection system based on intracavity fiber laser, REV SCI INSTRUM, 82 (2011). [13] Y. Zhang, M. Zhang, W. Jin, H.L. Ho, M.S. Demokan, B. Culshaw, G. Stewart, Investigation of erbiumdoped fiber laser intra-cavity absorption sensor for gas detection, OPT COMMUN, 232 (2004) 295-301. [14] K. Liu, W. Jing, G. Peng, J. Zhang, Y. Wang, T. Liu, D. Jia, H. Zhang, Y. Zhang, Wavelength Sweep of Intracavity Fiber Laser for Low Concentration Gas Detection, IEEE PHOTONIC TECH L, 20 (2008) 15151517. [15] K. Liu, T. Liu, J. Jiang, G. Peng, H. Zhang, D. Jia, Y. Wang, W. Jing, Y. Zhang, Investigation of Wavelength Modulation and Wavelength Sweep Techniques in Intracavity Fiber Laser for Gas Detection, J LIGHTWAVE TECHNOL, 29 (2011) 15-21. [16] G. Stewart, P. Shields, B. Culshaw, Development of fibre laser systems for ring-down and intracavity gas spectroscopy in the near-IR, MEAS SCI TECHNOL, 15 (2004) 1621-1628. [17] K. Krzempek, G. Dudzik, K. Abramski, Photothermal spectroscopy of CO2 in an intracavity modelocked fiber laser configuration, OPT EXPRESS, 26 (2018) 28861-28871. [18] Y. Ma, Y. He, L. Zhang, X. Yu, J. Zhang, R. Sun, F.K. Tittel, Ultra-high sensitive acetylene detection using quartz-enhanced photoacoustic spectroscopy with a fiber amplified diode laser and a 30.72 kHz quartz tuning fork, APPL PHYS LETT, 110 (2017). [19] Q. Wang, Z. Wang, W. Ren, Theoretical and Experimental Investigation of Fiber-Ring Laser Intracavity Photoacoustic Spectroscopy (FLI-PAS) for Acetylene Detection, J LIGHTWAVE TECHNOL, 35 (2017) 4519-4525. [20] Q. Wang, Z. Wang, W. Ren, P. Patimisco, A. Sampaolo, V. Spagnolo, Fiber-ring laser intracavity QEPAS gas sensor using a 7.2 kHz quartz tuning fork, SENSOR ACTUAT B-CHEM, 268 (2018) 512-518. [21] Q. Zhang, J. Chang, Q. Wang, Z. Wang, F. Wang, Z. Qin, Acousto-Optic Q-Switched Fiber Laser-Based Intra-Cavity Photoacoustic Spectroscopy for Trace Gas Detection, SENSORS-BASEL, 18 (2018). [22] Y. Ma, Y. He, Y. Tong, X. Yu, F.K. Tittel, Quartz-tuning-fork enhanced photothermal spectroscopy
for ultra-high sensitive trace gas detection, OPT EXPRESS, 26 (2018) 32103-32110. [23] Y. He, Y. Ma, Y. Tong, X. Yu, F.K. Tittel, Ultra-high sensitive light-induced thermoelastic spectroscopy sensor with a high Q-factor quartz tuning fork and a multipass cell, OPT LETT, 44 (2019) 1904-1907. [24] Z. Wu, Y. Zhang, H. Zhang, N. Gai, A photoacoustic spectroscopy measurement of near-infrared low-mass multi-component gas at room temperature and atmospheric pressure, MEASUREMENT, 139 (2019) 411-420. [25] C.J. Gaeta, M. Digonnet, H.J. Shaw, Pulse characteristics of Q-switched fiber lasers, J LIGHTWAVE TECHNOL, 5 (1987) 1645-1651. [26] C.W. Van Neste, L.R. Senesac, D. Yi, T. Thundat, Standoff detection of explosive residues using photothermal microcantilevers, APPL PHYS LETT, 92 (2008). [27] I.E. Gordon, L.S. Rothman, C. Hill, R.V. Kochanov, Y. Tan, P.F. Bernath, M. Birk, V. Boudon, A. Campargue, K.V. Chance, B.J. Drouin, J.M. Flaud, R.R. Gamache, J.T. Hodges, D. Jacquemart, V.I. Perevalov, A. Perrin, K.P. Shine, M.A.H. Smith, J. Tennyson, G.C. Toon, H. Tran, V.G. Tyuterev, A. Barbe, A.G. Csaszar, V.M. Devi, T. Furtenbacher, J.J. Harrison, J.M. Hartmann, A. Jolly, T.J. Johnson, T. Karman, I. Kleiner, A.A. Kyuberis, J. Loos, O.M. Lyulin, S.T. Massie, S.N. Mikhailenko, N. Moazzen-Ahmadi, H.S.P. Mueller, O.V. Naumenko, A.V. Nikitin, O.L. Polyansky, M. Rey, M. Rotger, S.W. Sharpe, K. Sung, E. Starikova, S.A. Tashkun, J. Vander Auwera, G. Wagner, J. Wilzewski, P. Wcislo, S. Yu, E.J. Zak, The HITRAN2016 molecular spectroscopic database, J QUANT SPECTROSC RA, 203 (2017) 3-69.
Highlights 1. A long-path QEPTS gas sensor using a high power Q-switched fiber laser was proposed. 2. Long optical path and high power are beneficial to the QEPTS sensor. 3. A minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time was achieved.
Declaration of Interest Statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser”
Jun Chang