scholarly journals A Dual-Laser Sensor Based on Off-Axis Integrated Cavity Output Spectroscopy and Time-Division Multiplexing Method

Sensors ◽  
2020 ◽  
Vol 20 (21) ◽  
pp. 6192
Author(s):  
Kunyang Wang ◽  
Ligang Shao ◽  
Jiajin Chen ◽  
Guishi Wang ◽  
Kun Liu ◽  
...  
Keyword(s):  
Limit Of Detection ◽  
Moving Average ◽  
Optical Cavity ◽  
Ambient Air ◽  
Laser Sensor ◽  
Time Division Multiplexing ◽  
Dual Channel ◽  
Cavity Output ◽  
Time Division ◽  
Dual Laser

In this article, a compact dual-laser sensor based on an off-axis integrated-cavity output spectroscopy and time-division multiplexing method is reported. A complete dual-channel optical structure is developed and integrated on an optical cavity, which allows two distributed feedback (DFB) lasers operating at wavelengths of 1603 nm and 1651 nm to measure the concentration of CO2 and CH4, simultaneously. Performances of the dual-laser sensor are experimentally evaluated by using standard air (with a mixture of CO2 and CH4). The limit of detection (LoD) is 0.271 ppm and 1.743 ppb at a 20 s for CO2 and CH4, respectively, and the noise equivalent absorption sensitivities are 2.68 × 10−10 cm−1 Hz−1/2 and 3.88 × 10−10 cm−1 Hz−1/2, respectively. Together with a commercial instrument, the dual-laser sensor is used to measure CO2 and CH4 concentration over 120 h and verify the regular operation of the sensor for the detection of ambient air. Furthermore, a first-order exponential moving average algorithm is implemented as an effective digital filtering method to estimate the gas concentration.

scholarly journals Validation of a new cavity ring-down spectrometer for measuring tropospheric gaseous hydrogen chloride

2021 ◽  
Author(s):  
Teles C. Furlani ◽  
Patrick R. Veres ◽  
Kathryn E. R. Dawe ◽  
J. Andrew Neuman ◽  
Steven S. Brown ◽  
...  
Keyword(s):  
Response Time ◽  
Hydrogen Chloride ◽  
Limit Of Detection ◽  
Optical Cavity ◽  
Ambient Air ◽  
Detection Methods ◽  
Ambient Atmosphere ◽  
Integration Interval ◽  
Mixing Ratios ◽  
Cavity Ring Down

Abstract. Reliable, sensitive, and widely available hydrogen chloride (HCl) measurements are important for understanding oxidation in many regions of the troposphere. We configured a commercial HCl cavity ring-down spectrometer (CRDS) for sampling HCl in the ambient atmosphere and developed calibration and validation techniques to characterize the measurement uncertainties. The CRDS makes fast, sensitive, and robust measurements of HCl in a high finesse optical cavity coupled to a laser centered at 5739 cm−1. The accuracy was determined to reside between 5–10 %, calculated from laboratory calibrations and an ambient air intercomparison with annular denuders. The precision and limit of detection (3σ) in the 0.5 Hz measurement were below 6 pptv and 18 pptv, respectively for a 30 second integration interval in zero air. The response time of this method is primarily characterized by fitting decay curves to a double exponential equation and is impacted by inlet adsorption/desorption, with these surface effects increasing with RH and decreasing with decreasing HCl mixing ratios. The response time for the tested inlet was 2–6 minutes under the most and least optimal conditions, respectively. An intercomparison with the EPA compendium method for quantification of acidic atmospheric gases showed good agreement, yielding a linear relationship statistically equivalent to unity (slope of 0.97 ± 0.15). The CRDS from this study can detect HCl at atmospherically relevant mixing ratios, often performing comparable or better in sensitivity, selectivity, and response-time from previously reported HCl detection methods.

Measurement of OH radicals using off-axis integrated output spectroscopy (OA-ICOS) at 2.8 µm

2021 ◽  
Author(s):  
Minh N. Ngo ◽  
Tong N. Ba ◽  
Denis Petitprez ◽  
Fabrice Cazier ◽  
Weixiong Zhao ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Near Infrared ◽  
Limit Of Detection ◽  
Optical Cavity ◽  
High Reactivity ◽  
Oh Radicals ◽  
Wavelength Modulation ◽  
Double Line ◽  
Trace Species ◽  
Cavity Output

<p>The hydroxyl (OH) free radical plays an important role in atmospheric chemistry due to its high reactivity with volatile organic compounds (VOCs) and trace species (CH<sub>4, </sub>CO, SO<sub>2</sub>, etc) [1]. Due to its very short lifetime (~1 s or less) and very low concentration in the atmosphere (in the order of 10<sup>6</sup> cm<sup>-</sup><sup>3</sup>), in situ and direct measurement of OH concentration in the atmosphere is challenging [2].</p><p>We report in this paper our recent work on developing a compact spectroscopic instrument based on off-axis integrated cavity output spectroscopy (OA-ICOS) [3] for optical monitoring of OH radicals. In the present work, OH radicals of ~10<sup>12</sup> OH radicals/cm<sup>3</sup> were generated from continue micro-wave discharge at 2.45 GHz of water vapor at low pressure (0.2-1 mbar), and were used as sample for validation of the developed OA-ICOS approaches. Two experimental approaches are designed for the measurements of OH radicals: (1) OA-ICOS [4] and wavelength modulation enhanced OA-ICOS (WM OA-ICOS) [5]. A distributed feedback (DFB) laser operating at 2.8 µm was employed for probing the Q (1.5e) and Q (1.5f) double-line transitions of the <sup>2</sup>Π<sub>3/2</sub><sub></sub>state at 3568.52382 and 3568.41693 cm<sup>-</sup><sup>1</sup>, respectively. A 1s detection limit of ~2.7×10<sup>10</sup> cm<sup>-3</sup>  was obtained for an averaging time of 125 s using a simple OA-ICOS scheme. This limit of detection is further improved by a factor of 3.4 using a WM OA-ICOS approach.</p><p>The experimental detail and the preliminary results will be presented and discussed.</p><p><strong> </strong><strong>Acknowledgments. </strong>The authors thank the financial supports from the CPER CLIMIBIO program and the Labex CaPPA project (ANR-10-LABX005).</p><p><strong>References</strong></p><p>[1]  U. Platt, M. Rateike, W. Junkermann, J. Rudolph, and D. H. Ehhalt, New tropospheric OH measurements, J. Geophys. Res. <strong>93</strong> (1988) 5159-5166.</p><p>[2]  D. E. Heard and M. J. Pilling, Measurement of OH and HO<sub>2</sub> in the Troposphere, Chem. Rev. <strong>103</strong> (2003) 5163-5198.</p><p>[3]  J. B. Paul, L. Lapson, J. G. Anderson, Ultrasensitive absorption spectroscopy with a high-finesse optical cavity and off-axis alignment, Appl. Opt. 40 (2001) 4904-4910.</p><p>[4]  W. Chen, A. A. Kosterev, F. K. Tittel, X. Gao, W. Zhao, "H<sub>2</sub>S trace concentration measurements using Off-Axis Integrated Cavity Output Spectroscopy in the near-infrared", Appl. Phys. B 90 (2008) 311-315</p><p>[5] W. Zhao, X. Gao, W. Chen, W. Zhang, T. Huang, T. Wu, H. Cha, Wavelength modulation off-axis integrated cavity output spectroscopy in the near infrared, Appl. Phys. B 86 (2007) 353-359</p>

scholarly journals Validation of a new cavity ring-down spectrometer for measuring tropospheric gaseous hydrogen chloride

2021 ◽  
Vol 14 (8) ◽  
pp. 5859-5871
Author(s):  
Teles C. Furlani ◽  
Patrick R. Veres ◽  
Kathryn E. R. Dawe ◽  
J. Andrew Neuman ◽  
Steven S. Brown ◽  
...  
Keyword(s):  
Response Time ◽  
Hydrogen Chloride ◽  
Limit Of Detection ◽  
Optical Cavity ◽  
Ambient Air ◽  
Detection Methods ◽  
Ambient Atmosphere ◽  
Integration Interval ◽  
Mixing Ratios ◽  
Cavity Ring Down

Abstract. Reliable, sensitive, and widely available hydrogen chloride (HCl) measurements are important for understanding oxidation in many regions of the troposphere. We configured a commercial HCl cavity ring-down spectrometer (CRDS) for sampling HCl in the ambient atmosphere and developed validation techniques to characterize the measurement uncertainties. The CRDS makes fast, sensitive, and robust measurements of HCl in a high-finesse optical cavity coupled to a laser centred at 5739 cm−1. The accuracy was determined to reside between 5 %–10 %, calculated from laboratory and ambient air intercomparisons with annular denuders. The precision and limit of detection (3σ) in the 0.5 Hz measurement were below 6 and 18 pptv, respectively, for a 30 s integration interval in zero air. The response time of this method is primarily characterized by fitting decay curves to a double exponential equation and is impacted by inlet adsorption/desorption, with these surface effects increasing with relative humidity and decreasing with decreasing HCl mixing ratios. The minimum 90 % response time was 10 s and the equilibrated response time for the tested inlet was 2–6 min under the most and least optimal conditions, respectively. An intercomparison with the EPA compendium method for quantification of acidic atmospheric gases showed good agreement, yielding a linear relationship statistically equivalent to unity (slope of 0.97 ± 0.15). The CRDS from this study can detect HCl at atmospherically relevant mixing ratios, often performing comparably or better in sensitivity, selectivity, and response time than previously reported HCl detection methods.

Full-parallax 3D display using time-multiplexing projection technology

2020 ◽  
Vol 2020 (2) ◽  
pp. 100-1-100-6
Author(s):  
Takuya Omura ◽  
Hayato Watanabe ◽  
Naoto Okaichi ◽  
Hisayuki Sasaki ◽  
Masahiro Kawakita
Keyword(s):  
Incident Light ◽  
Polarization State ◽  
3D Image ◽  
3D Display ◽  
Time Division Multiplexing ◽  
3D Images ◽  
Polarization Gratings ◽  
Light Rays ◽  
Time Division

We enhanced the resolution characteristics of a threedimensional (3D) image using time-division multiplexing methods in a full-parallax multi-view 3D display. A time-division light-ray shifting (TDLS) method is proposed that uses two polarization gratings (PGs). As PG changes the diffraction direction of light rays according to the polarization state of the incident light, this method can shift light rays approximately 7 mm in a diagonal direction by switching the polarization state of incident light and adjusting the distance between the PGs. We verified the effect on the characteristics of 3D images based on the extent of the shift. As a result, the resolution of a 3D image with depth is improved by shifting half a pitch of a multi-view image using the TDLS method, and the resolution of the image displayed near the screen is improved by shifting half a pixel of each viewpoint image with a wobbling method. These methods can easily enhance 3D characteristics with a small number of projectors.

Skin exposure: requirements to methods determining active ingredient of pesticides in washings

2019 ◽  
pp. 43-48
Author(s):  
V. N. Rakitskii ◽  
N. E. Fedorova ◽  
I. V. Bereznyak ◽  
N. G. Zavolokina ◽  
L. P. Muhina
Keyword(s):  
Lower Limit ◽  
Limit Of Detection ◽  
Solid Phase ◽  
Absorbed Dose ◽  
Ambient Air ◽  
Safety Coefficient ◽  
Limit Value ◽  
Calculated Risk ◽  
Nature Studies ◽  
Active Substances

The article presents results of studies exemplified by diquat on analysis concerning influence of lower limit value of quantitative assessment in washing sample for safety coefficient in exposure and in absorbed dose, if acting substance is absent in workplace ambient air samples and in dermal washings of workers. To control diquat in dermal washings, there is a method based on ion-pair liquid chromatography with ultraviolet detection (working wavelength 310 nm). To concentrate sample, cartridges for solid-phase extraction, containing ion exchange sorbent (Oasis MCX 6cc/500 mg), are used. Lower limit of assessment in washing sample — 0,15 micrograms. Experimentally set washing completeness is within range of 80–92%, standard deviation of repetition is 7,0% at most. The method created was tested in nature studies determining dermal exposure in workers subjected to 5 various preparations based on diquat dibromide when used for surface spraying from tractor and from aircraft. For lower limit of detection in washing sample (0,15 micrograms/washing), calculated risk value of exposure varied within 0,26–0,36; risk of absorbed dose was low — 0,23 (the allowable one ≤1). Findings are that present measuring methods which provide lower limit of detection 1 and 5 micrograms in washing sample could result in unallowable risk establishment even with absence of the substance in all samples of workplace air and dermal washings. The calculation formula suggested enables to give theoretic basis for requirements to lower limit of detecting active substances in dermal washing samples for evaluating risk of pesticides use in agriculture.

scholarly journals Demonstration of a Label-Free and Low-Cost Optical Cavity-Based Biosensor Using Streptavidin and C-Reactive Protein

Biosensors ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 4
Author(s):  
Donggee Rho ◽  
Seunghyun Kim
Keyword(s):  
Limit Of Detection ◽  
Point Of Care ◽  
Low Cost ◽  
Optical Cavity ◽  
Sample Volume ◽  
Small Sample ◽  
Label Free ◽  
C Reactive Protein ◽  
Reactive Protein ◽  
Cavity Structure

An optical cavity-based biosensor (OCB) has been developed for point-of-care (POC) applications. This label-free biosensor employs low-cost components and simple fabrication processes to lower the overall cost while achieving high sensitivity using a differential detection method. To experimentally demonstrate its limit of detection (LOD), we conducted biosensing experiments with streptavidin and C-reactive protein (CRP). The optical cavity structure was optimized further for better sensitivity and easier fluid control. We utilized the polymer swelling property to fine-tune the optical cavity width, which significantly improved the success rate to produce measurable samples. Four different concentrations of streptavidin were tested in triplicate, and the LOD of the OCB was determined to be 1.35 nM. The OCB also successfully detected three different concentrations of human CRP using biotinylated CRP antibody. The LOD for CRP detection was 377 pM. All measurements were done using a small sample volume of 15 µL within 30 min. By reducing the sensing area, improving the functionalization and passivation processes, and increasing the sample volume, the LOD of the OCB are estimated to be reduced further to the femto-molar range. Overall, the demonstrated capability of the OCB in the present work shows great potential to be used as a promising POC biosensor.

A Novel Multichannel Inductive Wear Debris Sensor Based on Time Division Multiplexing

2021 ◽  
Vol 21 (9) ◽  
pp. 11131-11139
Author(s):  
Sen Wu ◽  
Zhijian Liu ◽  
Kezhen Yu ◽  
Zixiao Fan ◽  
Ziyi Yuan ◽  
...  
Keyword(s):  
Wear Debris ◽  
Time Division Multiplexing ◽  
Time Division
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