Multiple Wavelength Infrared Emission Measurements to Determine Temperature, CO_2, H_2O, and CO Through Use of an Acousto Optic Tunable Filter

摘要

This paper presents the design of a system utilizing an acousto-optic tunable filter (AOTF) used in conjunction with infrared detection tools and fiber optics to determine the temperatures and column densities of H_2O, CO_2 and CO in a combustion effluent. An AOTF is a novel device that allows rapid narrow bandpass filter tuning in the UV, visible, and mid infrared spectral regions. The system under study uses a non-collinear TeO_2 crystal to measure irradiance in the mid infrared region in which spectral lines of high temperature H_2O, CO_2, and CO exist. Irradiance measurements are the convolution of the bandpass response of the AOTF and high temperature spectral emission species. Careful instrument calibration and construction of recursive algorithms is required to produce temperature and column density profiles. The AOTF is controlled electronically and can be rapidly tuned to wavelengths from 2 to 4.5 microns. The rapid tuning ability of the AOTF (about 15 ms per point) and hands free operation of the device makes it an attractive option for species profile characterization. Past system results and system performance using a scanning monochromator to simulate AOTF interaction will be discussed including column density and temperature profile measurements for various premixed flame concentrations. Initial results indicate that temperature and column densities of H_2O and CO_2 can be determined. Measurements of CO are more difficult but the spectral region near 2.325 μm shows promise for this measurement.