Optical absorption tomography for temperature and H2O concentration imaging by a compact photoelectric detecting system combined with twice adaptive algebraic algorithm

Tunable diode laser absorption spectroscopy is a robust method for simultaneous measurements of temperature and gas species. Different from commercial detectors integrated with photodiode receivers and amplifiers as the detecting system, a custom-made photoelectric detecting system comprised of Ge detectors and separated amplifiers was designed. First, Ge detectors received optical power from laser beams and then converted it into electrical current signals. The trans-impedance amplifiers were used to convert the current signals to voltage signals. The second stage amplifiers further amplified the voltage signals. All amplifiers that integrated the electronic circuits were packed in a portable case. Finally, the amplified voltage signals were received by data acquisition card. In this way, detectors could be arranged more compact and are easier to facilitate expandability. In addition, absorption data were reconstructed using twice adaptive algebraic reconstruction technique (AART) algorithm. During the reconstruction, after obtaining the temperature distribution through AART algorithm, AART algorithm was adopted for the second time for H2O concentration distribution. This system was validated with measurements of one-dimensional average temperature in a high temperature tube furnace and the system combined with twice adaptive algebraic algorithm demonstrated in a square flow field containing McKenna burners for simultaneous measurements of temperature and H2O distribution. The results indicated the viability and potential of this system combined with twice adaptive algebraic algorithm for sensitive temperature and H2O distribution tomography. (c) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)