Study On Oscillation Output Characteristics Of Pulse Timing Modulated Tunable Dye Laser

The combustion process is complex and variable,and the temperature is very high.Therefore,in order to obtain information about changes in the combustion field,non-contact measurement methods are usually employed.Planar Laser Induced Fluorescence(PLIF)is a typical non-contact measurement method and a general technology for combustion diagnosis.High-speed PLIF technology is suitable for non-steady-state fields and is a research hotspot in the field of diagnostic technology.The laser source is the core component of the high-speed PLIF diagnostic system.High-speed PLIF technology requires that the laser source possess the performance of high-frequency,high-energy,and output wavelengths in the ultraviolet range.Nowadays,the laser sources used in PLIF technology are mainly tunable dye lasers.Large energy dye laser systems typically include several parts,such as an oscillation,an amplifier stage,and a frequency conversion module.The seed light output of the oscillation directly determines the important indicators such as the output line width and tuning range of the entire tunable dye laser system.In this paper,the oscillation output characteristics of pulse timing modulation tunable dye lasers are studied.The research contents are as follows:According to the absorption line of the radical group generated during the combustion process,Rhodamine 6G methanol solution is selected as the laser system gain medium.The dispersion device in the cavity is initially selected from the fluorescent line of the dye molecule.The working principle of pulse timing modulation tunable dye laser is theoretically discussed,and the characteristics and tuning principle of the cavity are analyzed.The basic concept of beam quality factor and the measurement method used in the experiment are introduced.Under the condition that the expansion ratio in the cavity is 2 times,3 times and 4times respectively.The variation of the oscillating output energy with the grating grazing incidence angle under three conditions is studied in the experiment.The intracavity expansion ratio was determined.In the case of 4 times expansion,the output energy of the same grating grazing incidence angle is higher than the other two beam expansion ratios,and has a better line width narrowing effect.Then,the effects of diffraction efficiency of 1800 lines/mm,2400 lines/mm and3000 lines/mm grating on the oscillation output energy were studied.The grating elements in the cavity are determined.The 2400 line/mm grating blaze wavelength is closest to the peak wavelength of the dye molecule fluorescence line,the diffraction efficiency is the highest,and the oscillation output energy is large.For the 2400 line/mm grating,the influence of the grating grazing incidence angle on the tuning range and energy of the oscillating output wavelength is studied.The oscillation output wavelength tuning range and energy increase as the grating grazing incidence angle decreases.When the grazing incidence angle is about 87.0 degrees,the 2400 line/mm grating has a larger wavelength tunable range,higher output energy,and better line width narrowing.Finally,the effect of cavity length on the oscillating output energy and beam quality is studied.Increasing the length of the cavity will increase the loss and reduce the number of oscillations in the cavity.The cavity should be prevented from being too long.The beam waist radius and divergence angle of the output beam are oscillated by different cavity lengths to obtain beam quality factors at different cavity lengths.When the cavity length is short,the output beam quality is poor.Combined with two factors,the ideal cavity length of the resonant cavity is determined.Under this condition,the output energy of the amplification stage is 6mJ,and the light intensity distribution is more concentrated.