Kun Liu

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (13)17.07 Total impact

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    ABSTRACT: A detailed study on the temperature dependent characteristics of a wavelength modulated diode laser based photoacoustic (PA) detection system is presented. The temperature stability of the PA system and the temperature dependence of the resonance frequency, Q-factor, and cell constant of the resonator are investigated. The variation relationship between the cell constant and the Q-factor is compared with the changes of temperatures. The measurement of the system sensitivity shows that the PA system can be used to test trace gases in the upper troposphere and lower stratosphere. It provides the theoretical and experimental basis for the design of low temperature PA system.
    Optik - International Journal for Light and Electron Optics 08/2013; 124(16):2450–2454. · 0.77 Impact Factor
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    ABSTRACT: A homemade low-temperature, T shaped photoacoustic (PA) spectrometer is well established. The temperature stability and characteristics of the PA system in the temperature range of −90 to 0 °C were evaluated experimentally. A mathematical model for calculation of resonance frequencies and end-correction are proposed. The results of numerical calculations of the temperature dependent of resonant frequencies and the Q-factor of PA cell are compared with experimental measurements. The measured results show that the PA system has high Q-factor and the theoretical value is very well consistent with the experimental results. The variation of sensitivity of the PA system is very small in temperature range of −90 to 0 °C, which illustrates that the sensitivity of the microphone has little been affected by low temperature. So the system can be used in trace gas detection at low-temperature.
    Optics Communications 01/2013; 287:180–186. · 1.54 Impact Factor
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    ABSTRACT: Off beam quartz-enhanced photoacoustic spectroscopy (OB-QEPAS) sensors are based on a recently developed approach to off-beam photoacoustic (PA) detection which employs a quartz tuning fork (QTF) as an acoustic transducer. A microresonator (mR) with a side slit in the middle is used to enhance PA signal. This paper describes a theoretical model of an OB-QEPAS-based sensor. By deriving the acoustic impedances of the mR at two ends and the side slit in the middle in the model, we obtain a formula for numerically calculating the optimal mRs' parameters of OB-QEPAS-based sensor. We use the model to calculate the optimal mRs' lengths with respect to the resonant frequency of the QTF, acoustic velocities inside mRs, inner diameters of mRs, and acoustic conductivities of the mRs' side slits, and found out that the calculated results closely match experimental data. We also investigated the relationship between the mR selected in “on beam” QEPAS, OB-QEPAS, and an acoustic resonator (AR) excited in its first longitudinal mode used in conventional photoacoustic spectroscopy (PAS).
    Optics Communications 11/2012; 285(24):5306–5312. · 1.54 Impact Factor
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    ABSTRACT: A novel spectrophone sensor prototype consisting of a T-shaped acoustic microresonator (T-mR) in off-beam quartz-enhanced photoacoustic spectroscopy (T-mR QEPAS) is introduced for the first time. Its performance was evaluated and optimized through an acoustic model and experimental investigation via detection of water vapor in the atmosphere. The present work shows that the use of T-mR in QEPAS based sensor can improve the detection sensitivity by a factor of up to ~30, compared with that using only a bare QTF. This value is as high as that obtained in a conventional "on-beam" QEPAS, while keeping the advantages of "off-beam" QEPAS configuration: it is no longer necessary to couple excitation light beam through the narrow gap between the QTF prongs. In addition, the T-mR is really suitable for mass production with high precision.
    Optics Express 04/2012; 20(8):9187-96. · 3.53 Impact Factor
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    ABSTRACT: The development and performance of a cw, TE-cooled DFB quantum cascade laser based sensor for quantitative measurements of ammonia (NH3) and nitric oxide (NO) concentrations present in exhaled breath will be reported. Human breath contains ~ 500 different chemical species, usually at ultra low concentration levels, which can serve as biomarkers for the identification and monitoring of human diseases or wellness states. By monitoring NH3 concentration levels in exhaled breath a fast, non-invasive diagnostic method for treatment of patients with liver and kidney disorders, is feasible. The NH3 concentration measurements were performed with a 2f wavelength modulation quartz enhanced photoacoustic spectroscopy (QEPAS) technique, which is suitable for real time breath measurements, due to the fast gas exchange inside a compact QEPAS gas cell. A Hamamatsu air-cooled high heat load (HHL) packaged CW DFB-QCL is operated at 17.5°C, targeting the optimum interference free NH3 absorption line at 967.35 cm-1 (λ~10.34 μm), with ~ 20 mW of optical power. The sensor architecture includes a reference cell, filled with a 2000 ppmv NH3 :N2 mixture at 130 Torr, which is used for absorption line-locking. A minimum detection limit (1σ) for the line locked NH3 sensor is ~ 6 ppbv (with a 1σ 1 sec time resolution of the control electronics). This NH3 sensor was installed in late 2010 and is being clinically tested at St. Luke's Hospital in Bethlehem, PA.
    Proc SPIE 02/2012;
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    ABSTRACT: We will present the new progress in development of new generation trace gas sensors based on TDLAS and their application, including natural gas pipeline leakage detectors and new configurations of QEPAS sensors.
    Communications and Photonics Conference (ACP), 2012 Asia; 01/2012
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    ABSTRACT: Ultra-sensitive detection of nitrogen dioxide (NO2) in the ν3 fundamental band of NO2 using Faraday Rotation Spectroscopy (FRS) based optical sensor platform is reported. The FRS technique is well suited for selective trace gas measurements of paramagnetic species including the prominent air pollutants such as NO or NO2. In this paper a widely tunable external cavity quantum cascade laser (EC-QCL) is employed as an excitation source. The available EC-QCL mode-hop free tuning range between 1600 cm-1 and 1650 cm-1 allows to access the optimum for FRS technique 441<-440 Q-branch NO2 transition at 1613.2 cm-1 with an optical power of ~135 mW. In order to improve detection sensitivity and reduce size of the sensor platform, a custom made 22.47 cm long Herriott multipass gas cell (MPC) with a total effective optical path of 10.1 m was implemented. For a MPC configured NO2 FRS sensor operating in line-scanning mode a minimum detection limit of 1.6 ppbv (1σ) and 0.15 ppb (1σ) is achieved for a 1 sec and 100 sec averaging time, respectively. Preliminary results for long term measurements of atmospheric NO2 for the FRS sensor operating at an optimal pressure of 30 Torr and magnetic field of 200 Gaussrms were demonstrated.
    Proc SPIE 01/2012;
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    ABSTRACT: The effect of speed of sound (SoS) on the performance of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor was investigated. Methods to correct QEPAS signal and to minimize effect of SoS by the carrier gas was studied.
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    ABSTRACT: We applied for the first time, to our knowledge, broadband off-beam quartz-enhanced photoacoustic spectroscopy (BB-OB-QEPAS) to trace NO2 detection using a broadband blue laser diode centered at 450 nm. A detection limit of 18 ppbv (parts in 10(9) by volume) for NO2 in N2 at atmospheric pressure was achieved with an average laser power of 7 mW at a 1 s integration time, which corresponds to a 1 σ normalized noise equivalent absorption coefficient of 4.1×10(-9)  cm(-1) W=Hz(1=2). An Allan variance analysis was performed to investigate the long-term stability of the BB-OB-QEPAS-based NO2 sensor.
    Optics Letters 02/2011; 36(4):481-3. · 3.39 Impact Factor
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    ABSTRACT: A gas sensor based on off-beam quartz enhanced photoacoustic spectroscopy was developed and optimized. Specifically, the length and diameter of the microresonator tube were optimized, and the outer tube shape is modified for enhancing the trace gas detection sensitivity. The impact of the distance between the quartz tuning fork and an acoustic microresonator on the sensor performance was experimentally investigated. The sensor performance was evaluated by determining the detection sensitivity to H(2)O vapor in ambient air at normal atmospheric pressure. A normalized noise equivalent absorption coefficient (1σ) of 6.2×10(-9) cm(-1) W/Hz(1/2) was achieved.
    The Review of scientific instruments 10/2010; 81(10):103103. · 1.58 Impact Factor
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    ABSTRACT: An off-beam (OB) detection approach is suggested and experimentally investigated and optimized for quartz-enhanced photoacoustic spectroscopy (QEPAS). This OB-QEPAS configuration, very simple in assembly, not only allows for use of larger excitation optical beams and facilitating optical alignment but also provides higher enhancement of photoacoustic signals than previously published results based on the common on-beam QEPAS under the same experimental conditions. A normalized noise equivalent absorption coefficient (1sigma) of 5.9 x 10(-9) cm(-1)W/Hz(1/2) was obtained for water vapor detection at normal atmospheric pressure.
    Optics Letters 06/2009; 34(10):1594-6. · 3.18 Impact Factor
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    ABSTRACT: The HCN absorption spectrum from 6433 to 6613 cm<sup>-1</sup> was acquired at room temperature by means of a tunable external cavity diode laser based quartz-enhanced photoacoustic spectroscopy (QEPAS) technique.
    Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008

Publication Stats

62 Citations
17.07 Total Impact Points


  • 2009–2013
    • Chinese Academy of Sciences
      • Anhui Institute of Optics and Fine Mechanics
      Peping, Beijing, China
  • 2009–2012
    • Northeast Institute of Geography and Agroecology
      • Anhui Institute of Optics and Fine Mechanics
      Beijing, Beijing Shi, China