Development Of SESAM Mode Locked 500KHz,30W Picosecond Laser

With the development and progress of laser processing industry,the continuous improvement of the precision of processing has put forward higher requirements for the laser.In order to obtain stable laser output with narrow pulse width,using the absorber to achieve mode locking is an effective way.In this paper,a MOPA?Master Oscillator Power Amplifier?structure of SESAM mode-locked ultrafast lasers was developed,while maintaining narrow pulse width,high power and high beam quality picosecond mode-locked laser output was obtained,which can be applied to the field of laser fine machining and cold machining.The specific research work is as follows:1.The factors affecting the output power of SESAM mode-locked laser were analyzed by empirical formula,and the theoretical formulae of SESAM seed source and amplification stage were derived.The near-linear relationship between output power and pump power was obtained through MATLAB simulation analysis.2.The basic theory of SESAM mode-locking was studied,and the macroscopic parameters of SESAM were described in detail,including saturation recovery time,modulation depth,unsaturated loss,saturated flux and saturated light intensity.3.The relationship between the temperature gradient and the incident power was studied by establishing the steady state model of laser Nd:YVO₄ crystal.The COMSOL simulation software was used to simulate the thermal distribution of Nd:YVO₄ crystal under the condition of 10W?30W?60W?120W power laser incident.The characteristics of the thermal distribution of the crystal in steady state and the transverse and longitudinal temperature distribution trend at the highest temperature point were obtained,and the influence of the temperature distribution on the laser operation was analyzed.4.The SESAM mode-locked oscillator including seed source and RTP selectivity device was designed and developed to verify the above theoretical analysis.The experimental results show that when other parameters remain unchanged,the output power of the seed source increases with the increase of the pump power.Finally,a stable and good mode-locked pulse with a wavelength of 1064nm,a mode-locked pulse width of 16.3ps,a maximum output power of 3.39W,a beam mass M² factor of 1.12 and 1.07 in the x direction and y direction respectively,and an optical-optical conversion efficiency of 38%was obtained.5.A laser amplification stage was designed and constructed to further test the amplification characteristics of SESAM mode-locked ultrafine laser output pulses.We built a three-stage power amplifier with MOPA structure,the first of which was a four-course traveling wave amplifier,at a pump power of 18.66W;the seed light power was amplified to 3.84W.The secondary amplifier was a two-pass traveling wave amplifier,and the signal optical power was further amplified.At a pump power of 31.7W,the average signal optical power was amplified to 16.19W.Finally,after the third-stage one-pass traveling wave amplifier,at a pump light power of 100.4W,the average signal light power was amplified to 35.7W,the ideal pulse width and good beam quality were obtained,a high power laser output was obtained while the pulse width was guaranteed well,which provides a reference for the design of the same type of laser.