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Influence of exciting laser sheet intensity distribution on the fluorescence intensity distribution in a Planar Laser-induced Fluorescence(PLIF) experiment was analyzed.Based on cylindrical lens array,a laser sheet shaping system was designed.According to the requirement of PLIF,several parameters were optimized with ray tracing method.The laser beam shaping experiment system was established and applied to the PLIF experiment for dye laser beam shaping and acquiring smoothing laser sheet with the nonuniformity no more than 4%.With the uniformity laser sheet beam,PLIF was applied to the measurement of fluorescence imaging of OH in alcohol flame and CH4/air premixed combustion.

A molecular Filtered Rayleigh Scattering(FRS) diagnostic system was demonstrated to measure thermodynamic properties in combustion environments.The diagnostics system was composed of a narrow line width laser,a molecular/atomic absorption filter and a collection device such as ICCD.The absorption filter was used to modify the spectra of the Rayleigh scattering signal from the flow field illuminated by a laser sheet from a Nd:YAG pulsed laser.The laser was tuned to an absorption line of iodine vapor contained in the filter.This caused Mie scattering and background scattering from solid particles and strong absorption on the surface while much of Doppler broadened Rayleigh scattering was transmitted through the filter.The thermodynamic parameters were deduced from the measured transmission of the molecular Rayleigh scattering.The FRS diagnostic system and the iodine filter cell were described.On the basis of diagnosing FRS image and measuring iodine vapor absorption spectrum,the 2D temperature and density fields of methane/air premixed flame were obtained.The measured density at 15 mm above the burner surface is 0.19 kg/m3,and temperature is(1 827±84) K,which is good agreement with the results measured by using CARS method in the same condition.The uncertainty of temperature measurement by FRS is less than 8%.Furthermore,FRS technique was used to diagnose the atomization steam and supersonic exhaust flows.The results turbulence structures on the area of laser action were obtained.These demonstrate the abilities of the FRS technique to measure temperature and density fields and to enhance flow visualization in a combustion environment.

A multi-cavity passive nanosecond laser pulse stretching system was designed.The system could reduce laser peak powers and avoid the laser induced plasma spark,so that it reduces background interference and improves the signal to noise ratio in combustion diagnostics.The theoretical model of the pulse-stretching process for an arbitrary number of optical ring cavities was introduced,and several key parameters that affect on pulse width,beam-splitter reflectivity,cavity length and total number of optical cavities were analyzed.Finally,the designed multi-cavity laser pulse stretcher was used in broadening the Nd:YAG laser harmonic pulse width.Results indicate that a 7.8 ns input laser pulse has been converted into approximately the output laser pulses in 17 ns,35 ns and 72 ns,respectively.Furthermore,the laser peak power has been reduced to 9% of the original laser peak power,meanwhile,it maintains the good beam quality.The stretcher was also used in the spontaneous Raman scattering experiments,and results show it well resolves the laser induced breakdown spectroscopy of the Raman signal and achieves good results.

For the purpose of providing a method to estimate the effect of vibration on the optical performance of a burning diagnosis optical system,a numerical calculation method for the misaligned optical system under interference vibration was proposed.Based on the finite element analysis software ANSYS,the physical model of misaligned optical system under interference vibration was developed and the transient dynamic analysis was inspired by a reflector displacement in the vibration response.Then,the dynamic response of the reflector was obtained by transient dynamic analysis.On the basis of the matrix optics,geometrical optics theory and the mechanic vibration theory,the vibration misalignment matrix of planar reflector was analyzed,and the vibration misalignment model was also built.Meanwhile,the method of simulating calculation of misaligned optical system under interference vibration was inferred.Furthermore,an experiment was carried out to validate the method.The results show the the relative error of simulating calculation and experimental data can reach 4.1% and 0.8% in the horizontal and vertical directions,respectively.