scholarly journals A Laser-Based Multipass Absorption Sensor for Sub-ppm Detection of Methane, Acetylene and Ammonia

Sensors ◽  
2022 ◽  
Vol 22 (2) ◽  
pp. 556
Author(s):  
Wei Duan ◽  
Fuwu Yan ◽  
Yu Wang ◽  
Hui Zhang ◽  
Liuhao Ma ◽  
...  
Keyword(s):  
Detection Limit ◽  
Second Harmonic ◽  
Beam Steering ◽  
Optical Path Length ◽  
Integration Time ◽  
Gas Cell ◽  
Long Term Stability ◽  
Deviation Analysis ◽  
Time Flow ◽  
Sampling Volume

A compact, sensitive laser-based absorption sensor for multispecies monitoring of methane (CH4), acetylene (C2H2) and ammonia (NH3) was developed using a compact multipass gas cell. The gas cell is 8.8 cm long and has an effective optical path length of 3.0 m with a sampling volume of 75 mL. The sensor is composed of three fiber-coupled distributed feedback lasers operating near 1512 nm, 1532 nm and 1654 nm, an InGaAs photodetector and a custom-designed software for data acquisition, signal processing and display. The lasers were scanned over the target absorption features at 1 Hz. First-harmonic-normalized wavelength modulation spectroscopy (f = 3 kHz) with the second harmonic detection (WMS-2f/1f) is employed to eliminate the unwanted power fluctuations of the transmitted laser caused by aerosol/particles scattering, absorption and beam-steering. The multispecies sensor has excellent linear responses (R2 > 0.997) within the gas concentration range of 1–1000 ppm and shows a detection limit of 0.32 ppm for CH4, 0.16 ppm for C2H2 and 0.23 ppm for NH3 at 1 s response time. The Allan–Werle deviation analysis verifies the long-term stability of the sensor, indicating a minimal detection limit of 20–34 ppb were achieved after 60–148 s integration time. Flow test of the portable multispecies sensor is also demonstrated in this work.

Hollow waveguide-enhanced mid-infrared sensor for fast and sensitive ethylene detection

Sensor Review ◽  
2017 ◽  
Vol 37 (1) ◽  
pp. 82-87 ◽  
Author(s):  
Jinyi Li ◽  
Zhenhui Du ◽  
Zheyuan Zhang ◽  
Limei Song ◽  
Qinghua Guo
Keyword(s):  
Second Harmonic ◽  
Tunable Laser ◽  
Infrared Region ◽  
Integration Time ◽  
Hollow Waveguide ◽  
Gas Cell ◽  
Optical Source ◽  
Mid Infrared ◽  
Content Type ◽  
Sensor Platform

Purpose This paper aims to provide a sensor for fast, sensitive and selective ethylene (C2H4) concentration measurements. Design/methodology/approach The paper developed a sensor platform based on tunable laser absorption spectroscopy with a 3,266-nm interband cascade laser (ICL) as an optical source and a hollow waveguide (HWG) as a gas cell. The ICL wavelength was scanned across a C2H4 strong fundamental absorption band, and an interference-free C2H4 absorption line located at 3,060.76 cm−1 was selected. Wavelength modulation spectroscopy with the second harmonic detection (WMS-2f) technique was used to improve the sensitivity. Furthermore, the HWG gas cell can achieve a long optical path in a very small volume to improve the time response. Findings The results show excellent linearity of the measured 2f signal and the C2H4 concentration with a correlation coefficient of 0.9997. Also, the response time is as short as about 10 s. The Allan variance analysis indicates that the detection limit can achieve 53 ppb with an integration time of 24 s. Practical implications The ethylene sensor has many meaningful applications in environmental monitoring, industrial production, national security and the biomedicine field. Originality/value The paper provides a novel sensor architecture which can be a versatile sensor platform for fast and sensitive trace-gas detection in the mid-infrared region.

Interchangeable Range of Ozone Concentration Simulation for Low Cost Reconfigurable Brass Gas Cell

2014 ◽  
Vol 69 (8) ◽  
Author(s):  
Tay Ching En Marcus ◽  
Michael David ◽  
Maslina Yaacob ◽  
Mohd Rashidi Salim ◽  
Mohd Haniff Ibrahim ◽  
...  
Keyword(s):  
Theoretical Calculation ◽  
Ozone Concentration ◽  
Path Length ◽  
Low Cost ◽  
Cell Structure ◽  
Optical Path Length ◽  
Optical Path ◽  
Concentration Measurement ◽  
Gas Cell ◽  
Wide Range

Ultraviolet absorption spectroscopy is reliable for ozone concentration measurement. Concentration range and optical path length are inversely related based on theoretical calculation and observation of previous work. However, gas cells for ozone application are typically not expandable. In addition, they incur cost for custom fabrication. Here we design a reconfigurable brass gas cell that may interchange optical path length between 5.6 cm and 10.8 cm. Components are available at low cost, easy to joint and ready to use. Theoretical background and gas cell structure are discussed. Practical transmittance values between e-0.65 and e-0.05 are proposed for theoretical calculation of concentration via Beer-Lambert law. The concentration values are used in SpectralCalc.com gas cell simulation to obtain transmittance. Both approaches yield comparable result. Simulation result shows concentration range of 5.6 cm optical path length gas cell (31.82 ppm to 413.67 ppm) is wider than concentration range of 10.8 cm optical path length gas cell (16.50 ppm to 214.49 ppm). Simulation condition is at transmittance from 0.5291 to 0.9522, sampling wavelength 253.65 nm, temperature 300 K and pressure 1 atm. Thus, we strongly recommend short optical path length gas cell (5.6 cm) for wide range of concentration measurement (31.82 ppm to 413.67 ppm).

scholarly journals A Remote Raman System and Its Applications for Planetary Material Studies

Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 6973
Author(s):  
Hongkun Qu ◽  
Zongcheng Ling ◽  
Xiaobin Qi ◽  
Yanqing Xin ◽  
Changqing Liu ◽  
...  
Keyword(s):  
Raman Spectra ◽  
Second Harmonic ◽  
Signal To Noise Ratio ◽  
High Energy ◽  
Integration Time ◽  
Raman Signal ◽  
Charge Coupled Device ◽  
Water Ice ◽  
Good Signal ◽  
Material Studies

A remote Raman prototype with a function of excitation energy adjusting for the purpose of obtaining a Raman signal with good signal-to-noise ratio (SNR), saving power consumption, and possibly avoiding destroying a target by high energy pulses, which may have applications for Chinese planetary explorations, has been setup and demonstrated for detecting different minerals. The system consists of a spectrograph equipped with a thermoelectrically cooled charge-coupled device (CCD) detector, a telescope with 150 mm diameter and 1500 mm focus length, and a compact 1064 nm Nd:YAG Q-switched laser with an electrical adjusted pulse energy from 0 to 200 mJ/pulse. A KTP crystal was used for second harmonic generation in a 1064 nm laser to generate a 532 nm laser, which is the source of Raman scatting. Different laser pulse energies and integration time were used to obtain distinguishable remote Raman spectra of various samples. Results show that observed remote Raman spectra at a distance of 4 m enable us to identify silicates, carbonates, sulfates, perchlorates, water/water ice, and organics that have been found or may exist on extraterrestrial planets. Detailed Raman spectral assignments of the measured planetary materials and the feasible applications of remote Raman system for planetary explorations are discussed.

scholarly journals Application of Micro Quartz Tuning Fork in Trace Gas Sensing by Use of Quartz-Enhanced Photoacoustic Spectroscopy

Sensors ◽  
2019 ◽  
Vol 19 (23) ◽  
pp. 5240 ◽  
Author(s):  
Haoyang Lin ◽  
Zhao Huang ◽  
Ruifeng Kan ◽  
Huadan Zheng ◽  
Yihua Liu ◽  
...  
Keyword(s):  
Photoacoustic Spectroscopy ◽  
Tuning Fork ◽  
Gas Sensing ◽  
Modulation Depth ◽  
Quartz Tuning Fork ◽  
Acoustic Resonance ◽  
Photoacoustic Signal ◽  
Integration Time ◽  
Sampling Volume ◽  
Qepas Sensor

A novel quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a micro quartz tuning fork (QTF) is reported. As a photoacoustic transducer, a novel micro QTF was 3.7 times smaller than the usually used standard QTF, resulting in a gas sampling volume of ~0.1 mm3. As a proof of concept, water vapor in the air was detected by using 1.39 μm distributed feedback (DFB) laser. A detailed analysis of the performance of a QEPAS sensor based on the micro QTF was performed by detecting atmosphere H2O. The laser focus position and the laser modulation depth were optimized to improve the QEPAS excitation efficiency. A pair of acoustic micro resonators (AmRs) was assembled with the micro QTF in an on-beam configuration to enhance the photoacoustic signal. The AmRs geometry was optimized to amplify the acoustic resonance. With a 1 s integration time, a normalized noise equivalent absorption coefficient (NNEA) of 1.97 × 10−8 W·cm−1·Hz−1/2 was achieved when detecting H2O at less than 1 atm.

Doubled Optical Path Length for Photonic Bandgap Fiber Gas Cell Using Micromirror

2011 ◽  
Vol 50 (6) ◽  
pp. 06GM01 ◽  
Author(s):  
Xuefeng Li ◽  
Jinxing Liang ◽  
Hiroshi Oigawa ◽  
Toshitsugu Ueda
Keyword(s):  
Path Length ◽  
Photonic Bandgap ◽  
Optical Path Length ◽  
Optical Path ◽  
Gas Cell ◽  
Photonic Bandgap Fiber

scholarly journals A Trace C2H2 Sensor Based on an Absorption Spectrum Technique Using a Mid-Infrared Interband Cascade Laser

Micromachines ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 530 ◽  
Author(s):  
Ye Mu ◽  
Tianli Hu ◽  
He Gong ◽  
Ruiwen Ni ◽  
Shijun Li
Keyword(s):  
Absorption Spectroscopy ◽  
Second Harmonic ◽  
Harmonic Signal ◽  
Gas Absorption ◽  
Tunable Diode Laser ◽  
Integration Time ◽  
Detection Accuracy ◽  
Laser Absorption ◽  
Interband Cascade Laser ◽  
Diode Laser Absorption

In this study, tunable diode laser absorption spectroscopy (TDLAS) combined with wavelength modulation spectroscopy (WMS) was used to develop a trace C2H2 sensor based on the principle of gas absorption spectroscopy. The core of this sensor is an interband cascade laser that releases wavelength locks to the best absorption line of C2H2 at 3305 cm−1 (3026 nm) using a driving current and a working temperature control. As the detected result was influenced by 1/f noise caused by the laser or external environmental factors, the TDLAS-WMS technology was used to suppress the 1/f noise effectively, to obtain a better minimum detection limit (MDL) performance. The experimental results using C2H2 gas with five different concentrations show a good linear relationship between the peak value of the second harmonic signal and the gas concentration, with a linearity of 0.9987 and detection accuracy of 0.4%. In total, 1 ppmv of C2H2 gas sample was used for a 2 h observation experiment. The data show that the MDL is low as 1 ppbv at an integration time of 63 s. In addition, the sensor can be realized by changing the wavelength of the laser to detect a variety of gases, which shows the flexibility and practicability of the proposed sensor.

Detection of Anthracene in Real Water Samples with a Label-Free Amperometric Immunosenor

2011 ◽  
Vol 183-185 ◽  
pp. 547-551 ◽  
Author(s):  
Yan Zhang ◽  
Ping Ge Dian ◽  
Hui Sheng Zhuang
Keyword(s):  
Detection Limit ◽  
Prussian Blue ◽  
Water Samples ◽  
Gold Film ◽  
Polyclonal Antibodies ◽  
Current Response ◽  
Label Free ◽  
Long Term Stability

A label-free amperometric immunosenor for determination of anthracene was developed. Prussian blue was electrodeposited on the glassy carbon electrode and then modified with nanometer-size gold film to protect Prussian blue layer and immobilized anthracene polyclonal antibodies. The characteristics of the modified electrode at different stages of modification were studied by cyclic voltammetry. The performances of the amperometric immunosensor were studied in detail. At the optimal experimental condition, the current response of the immunosensor was proportional to the concentration of anthracene in the range of 1.8~90 ng•mL-1with a detection limit of 0.82 ng•mL-1(S/N=3). The studied immunosensor exhibited low detection limit, long-term stability and easy regenerated. This mothod was applied to the anthracene detection in river water samples with satisfied results.

Diphasic and Polyphasic Temporal Modulations Multiply Apparent Spatial Frequency

Perception ◽  
1974 ◽  
Vol 3 (3) ◽  
pp. 323-336 ◽  
Author(s):  
V Virsu ◽  
G Nyman ◽  
P K Lehtiö
Keyword(s):  
Spatial Frequency ◽  
High Frequency ◽  
Light Adaptation ◽  
Second Harmonic ◽  
Temporal Integration ◽  
Low Frequency ◽  
Integration Time ◽  
Sinusoidal Grating ◽  
Spatial Effects ◽  
Spatial Integration

The effects of diphasic and polyphasic flicker on apparent spatial frequency were studied in several experiments through simultaneous spatial-frequency matches. In diphasic flicker the spatial phase of a sinusoidal grating alternated between two values in a counterphase fashion, and in polyphasic flicker the spatial phases of gratings were varied discretely in time in a variable number of steps. Both forms of flicker increased the apparent spatial frequency at low temporal frequencies, in the same manner as low-frequency monophasic flicker has been found to do. At high temporal frequencies, diphasic flicker doubled the apparent spatial frequency, as reported by Kelly (1966). We found that through high-frequency polyphasic flicker the spatial effect that Kelly mentions can be generalised to spatial frequency multiplication: polyphasic flicker produces not only the apparent second harmonic but also the third and the fourth harmonic, depending on the phase parameters. A numerical analysis showed that the spatial high-frequency effects can be explained through temporal integration of nonlinearly filtered input signals if a value of 200 td(1) is assumed for the nonlinearity constant in [Formula: see text] where B( I) is the brightness, I is the retinal illuminance, K is a scale constant, and I½ is the constant of nonlinearity. A minimum value of 60 ms had to be estimated for integration time. An investigation of the integration time with diphasic flicker indicated that spatial integration time decreases when the level of light adaptation increases, and that the integration time for spatial effects is longer than for flicker fusion. The spatial effects of low-frequency and high-frequency flicker differ in so many respects that different neural processes have to be postulated for their explanation.

scholarly journals Investigation and Optimization of a Line-Locked Quartz Enhanced Spectrophone for Rapid Carbon Dioxide Measurement

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5225
Author(s):  
Hui Zhang ◽  
Wenling Jin ◽  
Mengpeng Hu ◽  
Mai Hu ◽  
Jingqiu Liang ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Detection Limit ◽  
Response Time ◽  
Co2 Concentration ◽  
Quartz Tuning Fork ◽  
Fast Response ◽  
Laser Wavelength ◽  
System Stability ◽  
Integration Time ◽  
Co2 Absorption

We have developed a rapid quartz enhanced spectrophone for carbon dioxide (CO2) measurement, in which the laser wavelength was tightly locked to a CO2 absorption line and a custom quartz tuning fork (QTF) operating at 12.5 kHz was employed. The intrinsic QTF oscillation-limited response time, as well as the optimal feedback interval, was experimentally investigated. By tightly locking the laser to the R(16) transition of CO2, we obtained a stable laser operation with its center wavelength variation kept within 0.0002 cm−1, merely three times the laser linewidth. The reported CO2 sensor achieved a detection limit of 7 ppm, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 4.7 × 10−9 W·cm−1·Hz−1/2, at a response time of 0.5 s. The detection limit can be further improved to 0.45 ppm at an integration time of 270 s, illustrating a good system stability. This spectrophone enables the realization of compact and fast-response gas sensors for many scenarios, where CO2 concentration from sub-ppm to hundreds of thousands of ppm is expected.

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