Diode Laser Absorption Spectroscopy Method Research Articles

Identification of ground spilled oil of buried pipeline based on laser absorption spectroscopy: Numerical investigation and experimental verification

The ground diffusion characteristics of buried oil pipeline after leakage and the laser optical transmission mechanism of surface oil film are the basis of spectral detection technology. Based on the computational fluid dynamics to solve the diffusion equation of multiphase flow in porous media, the leakage law of oil under different soil porosity is analyzed in two dimensions: surface diffusion diameter and oil film thickness. TracePro optical simulation is used to study the absorption and reflection patterns of laser at the oil-gas interface, and validation experiments are carried out based on the tunable diode laser absorption spectroscopy method. The results show that oil is easily accumulated on the ground surface with larger soil porosity and in the depressions of the ground surface. When the oil film thickness is greater than 2 mm, the laser cannot transmit the oil layer and the received light intensity is only provided by the mirror reflection at the oil-gas interface. The mechanism of laser detection of oil leaks is the spectral absorption of volatile alkane gases in the upper layer of the oil film by a laser of a specific wavelength.

Highly sensitive measurement of trace methane gas using mid‐infrared tunable diode laser absorption spectroscopy method

AbstractTo monitor the concentration of harmful gas methane (CH4) in the tunnel in real time, a high‐sensitivity measurement method for CH4 trace gas based on tunable diode laser absorption spectroscopy (TDLAS) is designed in this paper. An interband cascade laser with the emission wavelength of 3.29 μm was used to target noninterference CH4 lines at 3038.5 cm−1. To diminish the background noise of the sensor system, wavelength modulation spectroscopy combined with a second harmonic measurement technique was used in this work. Finally, 1.83 parts per billion in volume (ppbv) minimum measurement limit (MML) was obtained with a 4 s integration time based on an Allan‐Werle variance analysis, and the MML can be further improvedto ∼0.4 ppbv by increasing the integration time up to 104 s. Indoor and outdoor environmental data of CH4 acquired using the TDLAS sensor system are also reported.

Design of an electronic system for laser methane gas detectors using the tunable diode laser absorption spectroscopy method

In this paper, a new electronic system is designed for methane gas laser analyzers using the tunable diode laser absorption spectroscopy (TDLAS) technique. This electronic system is presented in such a way that, based on this technique, optical wavelength and stability confirm the power of the laser light source. The proposed design includes current and temperature control circuits, amplifier circuits, and laser sensor circuits. This system leads to the control of laser light power. Due to the high cost of a laser sensor distributed feedback diode (DFB) and the impossibility of purchasing it for the actual implementation of the proposed electronic system, the design and simulation stage of this system was performed in the proteus simulator environment at normal atmospheric temperature and constant control flow conditions. The simulation results show that the proposed new electronic system based on the TDLAS technique detected the amount of leaking methane gas by generating a wavelength of 1653.72 nm related to the DFB laser sensor and displaying it on display during calculation. The test of optical wavelength stability, optical power, and methane gas wavelength generation by the laser sensor in the proteus simulator environment at different distances is excellent and remarkable. These results show that if we buy a laser sensor and build a gas analyzer device, we can achieve perfect results by using the device with the provided technique.

Experimental measurement of collision broadening of vibrational-rotational spectral lines 12C16O2 and 13C16O2 in the 4860–4880 cm−1 region by diode laser absorption spectroscopy

The experimental measurement of the R(18), R(20), R(22), R(24), R(26), R(28), R(30), R(34), R(36) absorption lines collision broadening for the 12C16O2 molecule vibrational band 20013–00001 and P(10), P(12), P(14), P(16), P(18), P(20), P(22) absorption lines for the 13C16O2 molecule 20012–00001 vibrational band have been reported in this paper. The research has been first carried out by the diode laser absorption spectroscopy method using a single-frequency diode laser emitting in the 4860–4880 cm−1 region. The dependences of the absorption constants and cross-sections of these lines on the 13C16O2 and 12C16O2 molecules mixture concentrations in the ratio of 1:140 have been studied. The obtained results have been compared with the HITRAN spectroscopic database data.

Experimental observation of the vibration-rotation radiation curves of 12C16O2 and 13C16O2 absorption constants ranging from 4860 to 4880 sm−1 by the tunable diode laser absorption spectroscopy method

We report the experimental observation of the absorption constant values of 12C16О2 and 13C16О2 using the tunable diode laser absorption spectroscopy method ranging from 4860 to 4880 sm−1 within the pressure limits of 8–240 mbar for the absorption curves (lines) R(18), R(20), R(22), R(24), R(26), R(28), R(30), R(32), R(34) and R(36) of the 20013–00001 molecule 12C16О2 vibration band, and within the pressure limits of 0.06–1.7 mbar for the absorption curves P(10), P(12), P(14), P(16), P(18), P(20) and P(22) of the 20012–00001 molecule 13C16О2 vibration band. In the work, as a mixture under analysis, a mixture of the isotopes 13C16О2 and 12C16О2 at the ratio of 1:140 was used. The results have been compared with the data of the HITRAN spectroscopic database.

Application of the least square method for processing the signal obtained by the tuneable diode laser absorption spectroscopy method in the range 4860–4880 cm−1 for the problem of measuring 13CO2 content in exhaled air

The 1st, 2nd and 3rd order least square method (LSM-1, LSM-2 and LSM-3) is applied to smooth the experimental absorption signal of 13CO2 and 12CO2 obtained by the tuneable diode laser absorption spectroscopy method in the 4860–4880 cm−1 frequency range of a tuneable diode laser. It has been shown clearly that using LSM-2 with a filter window N ~ 100 allows the 13CO2 content in exhaled air to be measured at an error level of 0.28%, which meets breathing tests requirements.

Improving the 13CO2 content measurement accuracy in exhaled air using the Kalman technique for filtering the experimental signal obtained by the tunable diode laser absorption spectroscopy method with the frequency modulation of the diode laser pump current

This paper reports on the application of the Kalman method for processing the signal obtained by the tunable diode laser absorption spectroscopy method in an experimental circuit, which includes the frequency modulation of a diode laser pump current in combination with the synchronous detection technique. It has established that the implementing of this approach makes it possible to improve the measurement accuracy of the 13CO 2 content, as well as the measurement accuracy of the 13CO2 and 12CO2 concentrations ratio in exhaled air to a level not exceeding 0.1%.

Application of adaptive filters to improve online detection sensitivity of 13CO2 in a mixture with 12CO2 in expiratory air

The use of adaptive Kalman and Wiener filters and the empirical mode decomposition algorithm for processing the experimental signal obtained by the tunable diode laser absorption spectroscopy method has been reported to improve the sensitivity of the measurement of 13CO2 content in human expiratory air. A laser diode, tunable in the range 4860–4880 cm−1 near the wavelength of 2 µm, is used as a source. It has shown that the application of these filters ensures a detection sensitivity of 13CO2 at the level of 1015 cm−3, while the minimum detectable fraction of 13CO2 in a mixture with the 12CO2 is 3.8 · 10−5.

Improving the accuracy and sensitivity of 13C online detection in expiratory air using the TDLAS method in the spectral range of 4860–4880 cm−1

Implementing Kalman and Savitzky–Golay adaptive filters to process experimental signals and improve the sensitivity and accuracy of the measurements of the content of 13CO2 in human expiratory air with the tunable diode laser absorption spectroscopy method while using a laser diode as a tunable source in the range of 4860–4880 cm−1 near a wavelength of 2 µm has been reported. It is established that using these filters makes it possible to provide a detection sensitivity of 13CO2 at 5.5 · 1014 cm−3 with a minimum detectable fraction of 13CO2 in a mixture with 12CO2 of the order 2.1 · 10−5.

Flame Structure of Ammonium-Dinitramide-Based Liquid Propellant in a Small Thruster

In this paper, the flame structure of a liquid propellant ammonium dinitramide–methanol aqueous solution in a small model thruster is investigated. The thruster is composed of an injector and a combustion chamber (including a catalyst bed) with optical windows, through which the combustion process in the atmosphere is inspected, and the temperature distribution along the flame is measured by the tunable diode laser absorption spectroscopy method. Obvious fluctuations in temperature and flickering yellowish flame downstream of the combustion chamber are observed, indicating that the combustion is not stable. The mean temperature distribution has a significant peak where a yellowish flame appears. To explain the experimental observations, a detailed gas-phase ammonium dinitramide–methanol reaction model is used to establish the flame structure of an ideal liquid propellant, which can be divided into several different regions, including the liquid phase, aerosol zone, and two flame zones. The decomposition of ammonium dinitramide and the evaporation of methanol take place in the liquid phase and aerosol zone, whereas the gas phase reactions of methanol and the decomposition products of ammonium dinitramide take place in the two flame zones. Based on the proposed theory of flame structure, it is seen that, in our experiment, the physical and chemical processes in the liquid phase and aerosol zone are completed upstream of the catalyst bed, and the unstable yellowish flame appearing in the combustion chamber is caused by competitive influence between the two flame zones.

Investigation on liquid film of urea–water solutions with diode laser absorption spectroscopy

Measurement of multiparameter of liquid films (e.g., film thickness and concentration) is very important to understand the film formation processes in industrial applications. Here, a novel diode laser absorption spectroscopy (DLAS) sensor was developed to simultaneously measure the liquid film thickness and concentration of urea–water solutions by forming the transmittance ratio at two wavenumber positions. The performance of the sensor employed two diode lasers (6613.25 and 7187.50 cm−1) was first validated using a calibration tool providing liquid film of urea–water solutions with known film thickness (100–1000 μm) and mass fractions (5–50 wt%), and then, the sensor was applied to study a free-falling film of urea–water solutions on a vertical transparent quartz plate. Shadowgraph images were simultaneously taken as a means to obtain falling film thickness, and it was observed that measured film thickness was in good agreement with DLAS method and shadowgraph technique, and the deviation between these two techniques was 4.1 % when the falling film was stable.

Development of diode laser absorption spectroscopy method for determining temperature and concentration of molecules in remote object

We develop a method of diode laser absorption spectroscopy for noncontact measurements of the temperature and pressure of a gas mixture under unsteady-state conditions at low signal-to-noise ratios. The method is based on the measurement of the absorption spectra of water molecules and approximation of experimental spectra by spectra simulated based on spectroscopic databases. Different approximation algorithms of experimental spectra are tested, such as fitting by individual contours and fitting by a part of the simulated spectrum. We reveal that, at small signal-to-noise ratios, the approximation of experimental data by a simulated spectrum yields more correct data on the temperature of the mixture compared to the fitting by individual contours. For the examined temperature range of 300–1300 K, the determination error of the gas temperature in the test cell proved to be approximately three times lower than upon fitting by individual contours. The developed method of recording and processing spectra is used to measure the temperature, water vapor concentration, and total pressure under the unsteady-state combustion conditions of an air-hydrogen mixture in a supersonic flow.

Tunable diode laser absorption spectroscopy of argon metastable atoms in Ar/C2H2 dusty plasmas

The tunable diode laser absorption spectroscopy method was used to measure Ar metastable density in order to study the dust growth process in hydrocarbon-containing plasmas. A simple model was proposed that successfully interprets the experimental results of pristine plasmas. The model is also suitable for explaining the influence of dust particle size on metastable density and for examining the dust growth process. The metastable density responded strictly to the formation of dust particles and their growth in processing plasmas. Using metastable density as an indicator is, therefore, a non-intrusive and effective method for the study of the dust growth process in hydrocarbon-containing plasmas.

Atmospheric measurements of nitrogen dioxide with a sensitive luminol instrument

A highly sensitive, lightweight, portable instrument has been developed for continuous monitoring of N02 in air. It operates by detecting the chemiluminescence produced when N02 encounters a surface wetted with a specially formulated solution containing luminol. Unlike other chemiluminescent instruments it measures N02 directly and does not require prior conversion of N02 to NO. It does not respond to H202, NO, HNO3, NH3, CO, C02, S02 or organic nitrates. The only interferences encountered to date are from 03 and PAN with the response to 03 being less than 0.2% of its response to N02. The response time of the instrument is less than 1 s and its sensitivity is better than 5 pptv. The instrument shows a negative temperature dependence of about 2% °C−1 which is compensated electronically. Measurements have been made with the instrument during a number of field missions in polluted urban and relatively clean rural air. The relative influences of photochemistry and transport from local sources has been observed. Simultaneous measurements made with this instrument and the unequivocal tunable diode laser absorption spectroscopy method have shown excellent agreement.