Development Of High Energy Double Wavelength Output Nano-second Pulsed Optical Parametric At 1.54 ?M And 3.4 7?m

With the rapid developments of laser technologies and laser detection technologies,the applications of high-power or large-energy lasers in the fields of space communications,laser radar,illumination and identification have attracted more and more attentions and have been widely studied.The lasers whose wavelengths are at 1.5?m or between 3-5?m have many advantages in these applications than the 1.06?m competitors.The wavelengths of about 1.5?m or between 3-5?m are located in the atmospheric propagation window.Consequently,they are suitable for long-distance detection because of the faint atmospheric absorption coefficients in these spectral ranges.Also the lasers in these spectral ranges have lower sunlight disturbance and can get higher signal to noise ratio than the 1.06?m lasers in the daytime detection.The lasers with the characteristics of low energy consumption,compact volume,easy maintenance,and high stability are required in the actual applications.The laser which can emit radiations in both 1.5?m and 3-5?m spectral ranges will have important application values.In this thesis,a high pulse energy optical parametric oscillator based on KTiOAsO4(KTA)crystal with a pulse repetition rate of 100Hz and two wavelengths at 1.54?m and 3.47?m is presented The main research contents include three parts1.Theoretical analysis for the KTA optical parametric oscillator.The threshold and output efficiency are analyzed based on the coupled wave equations.The noncritical phase matching condition is calculated.By comprehensive analysis for all the factors,the design scheme and optimization idea are determined.2.Development of the electro-optically Q-switched 1064nm Nd:YAG laser.This laser will be used as the pumping source of the KTA optical parametric oscillator.The laser cavity is a positive branch unstable cavity.It consists of a concave total-reflection mirror and a convex output coupler with variable reflectivity.The cavity length is optimized.The influences of the crystal thermal effect on the laser transversal mode and output properties are analyzed.The obtained single pulse energy,pulse repetition rate,and pulse width are 50.7mJ,100Hz,and 12.8ns,respectively The corresponding electro-optical and optical-optical conversion efficiencies are 6.7%and 13.3%,respectively.The average power is 5.07W.The line width of the pulsed laser is less than 0.2nm.The output beam is a fundamental transverse mode Gaussian beam with a waist radius of 1mm.The horizontal and vertical beam quality factors are Mx2=2.41 and My2=1.88,respectively.3.Development of the extracavity-pumped 1.54?m and 3.47?m dual-wavelength optical parametric oscillator based on KTA crystal.The ?-type noncritical phase matching method is adopted.The oscillator is a two-mirror straight cavity.The pumping beam passes through the KTA crystal in a single trip way.The conversion efficiency is maximized by optimizing the output mirror reflectance and the number of cascaded KTA crystals.According to the result of analysis,three KTA crystals with a size of 5×5×25mm3 are used.The obtained laser pulse energies at 1.54?m and 3.47?m are 18.3mJ and 3.2mJ,respectively.The corresponding pump light conversion efficiency is 43.8%.The beam divergence is less than 0.44mrad.The pump source and the parametric oscillator are integrated into a complete set of equipment by elaborate engineering design.Finally,the 100Hz dual-wavelength light source with small volume,high stability,and high energy is realized.In the measurement of stability,the energy standard deviation of the whole device is 0.7%in 300s.