Towards simultaneous calibration-free and ultra-fast sensing of temperature and species in the intrapulse mode

Abstract

Towards simultaneous calibration-free and ultra-fast sensing of temperature and species in the intrapulse mode KAUST Repository Abstract:We report on exploiting the down-chirp phenomenon seen in quantum cascade lasers (QCLs), when modulated with long pulses, for the purpose of performing calibration-free and temporally resolved measurements. Intrapulse spectra of a native species (e.g. H 2 O), common to combustion environments, were generated near λ=7.62 µm at repetition rates as high as 3.125 MHz. Two-line absorption spectroscopy was employed to infer calibration-free temperature from the chirp-induced intrapulse spectra. In this study, such temperature measurements were limited to rates of 250 kHz due to spectral distortion at higher repetition rates. We demonstrate the ease at which accurate temperatures and H 2 O compositions can be achieved using simple and compact QCLs operated in the intrapulse mode. The sensor is also applicable to other species, and has the potential to be integrated into commercial technologies.

Ultra-fast and calibration-free temperature sensing in the intrapulse mode

“…Here, we showcase uncluttered, spectrally-pure Voigt profile fitting with accompanying peak SNRs of 150, resulting in a typical temperature precision of 0.9% (1σ) at an effective time-resolution of 1.0 MHz. Our sensor is applicable to other species, and can be integrated into commercial technologies.Accurate, precise, and noninvasive sensing obtainable by laser diagnostics is invaluable to applications such as chemistry, environmental monitoring, and combustion research [1][2][3][4]. Time-resolved diagnostics are essential to study transient phenomena, for example, as seen in explosions, internal combustion engines, gas turbines, and shock tubes.…”

Propene concentration sensing for combustion gases using quantum-cascade laser absorption near 11 μm

“…Reflected shock temperatures (T 5 ) and pressures (P 5 ) are determined from the measured incident shock speed and the standard 1D shock-jump relations. Further details of this shock tube can be found elsewhere [4,13].…”

“…The differential absorbance scheme can be summarized by Eqs. (1)(2)(3)(4). Absorption of monochromatic radiation is described by the Beer-Lambert law:…”

“…Such a laser diagnostic is a first step to experimentally determining propene in real time with sufficient time resolution, thus aiding the refinement and development of chemical kinetic models for combustion. multivariable approach through the measurement of species concentrations and temperature time profiles [3][4][5][6][7], chiefly using laser diagnostics.…”

Temperature imaging in low-pressure flames using diode laser two-line atomic fluorescence employing a novel indium seeding technique

“…Absorption based techniques benefit from experimental simplicity and straight-forward data evaluation and numerous papers present temperature measurements utilizing absorption techniques either based on near infrared diode lasers or quantum cascade lasers [11,12].…”