Single Tunable Diode Laser Research Articles

A simple sensor for simultaneous measurements of OH, H2O, and temperature in combustion environments using a single tunable diode laser near 1.477 μm

A simple sensor for simultaneous measurements of OH, H2O, and temperature in combustion environments using a single tunable diode laser near 1.477 μm

Simultaneous and interference-free measurements of temperature and C2H4 concentration using a single tunable diode laser at 1.62 µm.

In the tunable diode laser absorption spectroscopy-based diagnostics, the absorption of the measured target species may be influenced by the interference absorption from other vapor-phase species and the extinction from particles and liquid droplets, especially at high temperatures and pressures. Here, we report the first application (to our knowledge) of a differential absorption diagnostic for interference-free, simultaneous measurement of temperature and ethylene concentration using a single distributed-feedback diode laser near 1.62 μm. According to the detailed study of the C2H4 spectra in this region, two wavelength pairs are chosen to measure the temperature based on six selection criteria. C2H4 concentration is measured by one of the selected wavelength pairs with higher differential absorption. To validate the developed system, experiments are performed in a well-controlled heated static cell at a range of temperatures (300-900 K) and pressures (1-6 atm). The measurement accuracies for temperature and ethylene concentration are 1.83% and 1.65%, respectively, over the considered ranges. The precision, stability, and detection limit are also analyzed to validate the system's performance. This system can potentially be applied in a variety of combustion applications.

Broad-Range Detection of Water Vapor using Cavity Ring-down Spectrometer

Quantitative measurement of water vapor is essential in many fields including semiconductor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy. The instrument is high-vacuum compatible, self-calibrated by using the free-spectral-range of the ring-down cavity made of low-thermal-expansion Invar. Using a single tunable diode laser working at 1.39 µm, detection of trace water vapor in vacuum and in high-purity helium gas, and also determination of humidity at ambient conditions, have been demonstrated. It indicates that the instrument can be used to detect the partial pressure of water vapor in a very broad range from 10−7 Pa to 103 Pa. Such an optical hygrometer can be potentially applied as a primary moisture standard to determine the vapor pressures of water (ice) at low temperatures.

In situ H2O and temperature detection close to burning biomass pellets using calibration-free wavelength modulation spectroscopy

The design and application of an H2O/temperature sensor based on scanned calibration-free wavelength modulation spectroscopy (CF-WMS) and a single tunable diode laser at 1.4 μm is presented. The se ...

Design of a fibre optic sequential multipoint sensor for methane detection using a single tunable diode laser near 1666 nm

The design of a fibre optic sequential multipoint sensor using a single DFB laser source for measurement of average concentration of methane has been reported. A theoretical model for sequential multipoint sensor is developed. The validation of the sensor is conducted using methane gas cells connected in series via fibre optics to form 2-Cell and 3-Cell networks. The second harmonic detection of wavelength modulation spectroscopy (2f-WMS) is employed. Normalisation of the 2f signals with respect to the laser average intensity and the detector gain is used to correct for transmission variation. The measurements are performed at four laser modulation depths to compare the 2f-WMS signals for the target test conditions. The Q(6) transition of the 2v3 band of methane near 1666nm has been selected because the transition is relatively free of interference from water vapour and absorption by other major gases in that region. The sequential multipoint sensor has some unique advantages over the single cell and multiplexed multipoint sensors. These include the average concentration measurements, the use of only a single laser source, a detector, and a fibre optic to connect series of gas cells, no need for multiplexing techniques to distribute the laser intensity among multi gas cells, and relatively simpler data analysis.

Spatial resolved temperature measurement based on absorption spectroscopy using a single tunable diode laser

A novel method based on wavelength-multiplexed line-of-sight absorption and profile fitting for non-uniform flow field measurement is reported. A wavelength scanning combing laser temperature and current modulation WMS scheme is used to implement the wavelength-multiplexed-profile fitting method. Second harmonic (2f) signal of eight H2O transitions features near 7,170 cm−1 are measured in one period using a single tunable diode laser. Spatial resolved temperature distribution upon a CH4/air premixed flat flame burner is obtained. The result validates the feasibility of strategy for non-uniform flow field diagnostics by means of WMS-2f TDLAS.

A sensor for measurements of temperature and water concentration using a single tunable diode laser near 1.4 μm

Gas temperature and water concentration are measured by a tunable diode laser sensor using a single laser near 1.4 μm. Temperature is determined from the ratio of absorption of a H 2O line pair near 7079.176 and 7079.855 cm −1, which are chosen using some selected criteria. The second harmonic detection of wavelength modulation spectroscopy (WMS-2 f) is employed to improve the sensor sensitivity and accuracy. Normalization of the 2 f signal with the 1 f signal magnitude is used to remove the need for calibration and correct for transmission variation due to beam steering, mechanical misalignments, soot, and windows fouling. An optimum laser modulation depth is selected to make the WMS-2 f signals of both lines as big as possible for the target test conditions. The influence of total pressure and water mole fraction is evaluated through theoretical simulations. The validation of the sensor is conducted in a controlled static cell, yielding an accuracy of 1.06% temperature and 1.9% for H 2O concentration. Burner experiments demonstrate the accuracy (1.2% for temperature and 3.2% for H 2O concentration) and potential utility of the system for combustion diagnosis.

Development of a fast temperature sensor for combustion gases using a single tunable diode laser

The 12 best NIR water transition line pairs for temperature measurements with a single DFB laser in flames are determined by systematic analysis of the HITRAN simulation of the water spectra in the 1–2 μm spectral region. A specific line pair near 1.4 μm was targeted for non-intrusive measurements of gas temperature in combustion systems using a scanned-wavelength technique with wavelength modulation and 2f detection. This sensor uses a single diode laser (distributed-feedback), operating near 1.4 μm and is wavelength scanned over a pair of H2O absorption transitions (7154.354 cm-1 & 7153.748 cm-1) at a 2 kHz repetition rate. The wavelength is modulated (f=500 kHz) with modulation amplitude a=0.056 cm-1. Gas temperature is inferred from the ratio of the second harmonic signals of the two selected H2O transitions. The fiber-coupled-single-laser design makes the system compact, rugged, low cost and simple to assemble. As part of the sensor development effort, design rules were applied to optimize the line selection, and fundamental spectroscopic parameters of the selected transitions were determined via laboratory measurements including the temperature-dependent line strength, self-broadening coefficients, and air-broadening coefficients. The new sensor design includes considerations of hardware and software to enable fast data acquisition and analysis; a temperature readout rate of 2 kHz was demonstrated for measurements in a laboratory flame at atmospheric pressure. The combination of scanned-wavelength and wavelength-modulation minimizes interference from emission and beam steering, resulting in a robust temperature sensor that is promising for combustion control applications.

Development of a sensor for temperature and water concentration in combustiongases using a single tunable diode laser

The water vapour spectrum in the 1–2 µmnear-infrared region is systematically analysed to find the bestabsorption transitions for sensitive measurement of H2Oconcentration and temperature in combustion environments using a single tunable diodelaser with typical distributed feedback single-mode scanning range (1 cm−1).The use of a single laser, even with relatively narrow tuning range, canoffer distinct advantages over wavelength-multiplexing techniques. Thestrategy and spectroscopic criteria for selecting optimum wavelengthregions and absorption line combinations are discussed. It should bestressed that no single figure of merit can be derived to simplify theselection process, and the optimum line pair should be chosen case bycase. Our investigation reveals that the 1.8 µmspectral region is especially promising, and we have identified 10of the best water line pairs in this spectral region for temperaturemeasurements in flames. Based on these findings, a pair of H2Otransitions near 1.8 µmwas targeted for the design and development of an initialsingle-laser sensor for simultaneously measuring H2Oconcentration and temperature in atmospheric-pressure flames. As part of thesensor development effort, fundamental spectroscopic parameters includingthe line strength, line-centre frequency and lower state energies of theprobed transitions were measured experimentally to improve the currentdatabases. We conclude with demonstration results in a steady and a forcedatmospheric-pressure laboratory combustor.