Study On High-energy Nanosecond Fiber Laser And Its Frequency-doubling Output Characteristics

Pulsed fiber laser has been widely used in various fields because of its excellent performance,and the green light obtained by fiber laser frequency-doubling has great potential due to its lower price and good optical properties.A study on the output characteristics of acousto-optic Qswitched nanosecond pulsed fiber laser and frequency-doubling was carried out.The main research contents are as follows:1.This thesis first introduces the key devices and their corresponding principles of acousto-optic Q-switched fiber laser.Then two producing processes are proposed for cladding power stripper(CPS).The experimental results show that the cladding laser can be stripped uniformly by gradient corrosion method,and there is no obvious hot spot in the stripping section.When stripping 125 W cladding laser,the stripping degree is about 14.1d B and the maximum temperature of the stripping section is not more than 40 ℃.2.Next,the output characteristics of acousto-optic Q-switched fiber laser are studied experimentally.The test results of the seed source show that the output power increases with the increase of repetition rate while the pulse width decreases.The research results of pulsed amplifier show that : the gain fiber has an optimal length,too short or too long will reduce the pump efficiency;when the pump power is fixed,the shorter the length of gain fiber the easier the amplify spontaneous emission(ASE)appear;the weak change of pump current of seed source has no obvious effect on the output power of pulsed amplifier,but it is easy to cause multi-peak phenomenon of pulse waveform;the damage position of gain fiber has a certain regularity,that is,the damage point is approximately 20～50 cm from the fusion point of the pump combiner and gain fiber.The pulsed laser output with repetition rate of 50 k Hz and average power of 100 W is obtained in the experiment,the single pulse energy is 2m J and the light-light efficiency reaches 67.1%.3.The frequency-doubling experiments of nonlinear crystals,KTP and LBO are carried out.The research results show that the frequency-doubling efficiency of KTP crystal is higher,reaching 9.9%,but its damage threshold is lower.The frequency-doubling results of LBO crystal show that: the fiber laser with the center wavelength of 1064 nm should adopt I type phase matching mode in the X-Y plane corresponding to phase matching angle θ=90°,φ=11.3°;the frequency-doubling efficiency does not satisfy the proportional relationship with the length of the crystal,but by adjusting the temperature of LBO crystal,the adverse effects of walking angle can be compensated when the length of crystal increases;in addition,the frequency-doubling performance can be improved obviously by increasing the polarization of fundamental laser.Finally,by using a pulsed fiber amplifier with high peak power and an average power of 32.7 W,the experiment obtains green light with output power of 12.5W and the center wavelength of 532 nm,and the conversion efficiency is 39.6%.