Research On Diode-pumped High-power Kerr-lens Mode-locking All-solid-state Femtosecond Lasers

Ultrafast laser has broad application prospects in basic scientific research,information communication,biomedicine,micro-nano processing and national defense military due to it's unique advantages such as extremely short pulse duration,wide spectral bandwidth and high peak power.Laser-diode?LD?-pumped all-solid-state ultrafast lasers have been widely studied for their high efficiency,low price,compact structure and easy maintenance.This paper focuses on the research of LD pumped high power Kerr-lens mode-locked all-solid-state femtosecond lasers in near infrared band.The main contents and innovations of this paper are summarized as follows:1.The passive mode locking properties of SESAM for Nd,Y:CaF₂ disordered crystals were experimentally studied.The cavity type was a Z-folding cavity and the Nd,Y:CaF₂ crystal was pumped by LD,the maximum output power of continuous wave was 360 mW.GTI mirrors was used to compensate the intracavity dispersion,and the SESAM was used to implement mode-locking operation.The center wavelength,pulses duration and spectrum width of the mode-locked laser pulses were 1068 nm,220 fs and 5.5 nm,respectively,the maximum average output power was 195 mW,and the repetition frequency was 85 MHz.2.We demonstrate a high-power Kerr-lens mode-locked Yb:CYA oscillator pumped by multi-mode LD.A double-focus cavity was used to separate the gain medium from the Kerr medium,which overcomes the difficulty of the laser crystal in the traditional Kerr lens mode-locking as both the gain medium and the Kerr medium,the LD-pumped high-power Kerr lens mode-locking Yb:CYA laser is feasible.In the experiment,LD with a maximum output power of 50 W and an output wavelength of 976 nm was used as the pump source.2 mm thickness of quartz was used as the Kerr medium,and a 6 mm long Yb:CYA crystal doped with 5 at.%Yb³⁺was used as the gain medium.OC with a transmittance of 2.5%was used,maximum average output power of 1.5 W with pulse width of 99 fs was obtained,and the corresponding single-pulse energy and peak power were 30 nJ and 267 KW,respectively;for 5%OC,average output power of 2.5 W with pulse width of 70 fs was obtained,corresponding to a single pulse energy and peak power of 50 nJ and 0.62 MW,respectively;increasing the transmittance of OC to 15%,a high-power mode-locked laser with maximum average output power of 5.4 W and 79 fs pulses was obtained,the corresponding single-pulse energy and peak power were 108 nJ and 1.21 MW,respectively.3.In addition,CaF₂ with smaller nonlinear refractive index was used as the Kerr medium to realize high-power Kerr lens mode-locking operation.For 15%OC,the Yb:CYA laser directly produced 59 fs pulses with 6.2 W of average output power,the corresponding single pulse energy and peak power are 121 nJ.and 1.85 MW,which is the highest single-pulse energy from Yb-doped oscillators.By further optimizing the intracavity dispersion,pulse width as short as 54 fs with an average output power of 5.4 W was obtained.