An Optical Ray Tracing Method for Analyzing Beam-Steering Effects During Laser Diagnostics in Turbulent Media Conference Paper uri icon

abstract

  • © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Nonintrusive, laser-based diagnostic methods can provide valuable information of chemical species, temperature and other flow parameters in reacting flow systems such as flames and plasmas. When employing nonlinear laser spectroscopic schemes necessitating multiple laser beams to focus and cross at a particular spatial location to form the probe volume, beam steering effects resulting from refractive index gradients in the medium can introduce significant measurement uncertainties. Large density gradients present across turbulent reaction zones in laboratory-scale flames as well as practical devices such as gas turbine combustors and internal combustion engines. Resulting refractive index variations can cause beam steering effects when applying optical diagnostics and can introduce significant measurement uncertainties. The objective of this study is to characterize beam steering effects resulting from temperature and pressure gradients in the medium using an optical ray tracing approach. The ZEMAX OpticStudio® software package is used to analyze beam crossing, uncrossing effects in the presence of temperature and pressure gradients in the medium in selected experimental configurations. The model formulation, analysis of pressure and temperature gradients, and resulting beam-steering effects are discussed. While thermal gradients in the range of 300–3000 K are found to have minimal effects, pressure gradients in the range of 1–50 atm can cause significant beam steering and results in fluctuations of nonlinear signal generation. However, at elevated pressures, the temperature fluctuations can also have a noticeable effect on the resultant single levels.

author list (cited authors)

  • Kulatilaka, W. D., & Wang, Y.

publication date

  • January 1, 2016 11:11 AM