Research On LD Pumped Nd:YVO₄ Passively Mode-locked Laser And Intracavity Frequency-doubled

All-solid-state lasers have many advantages such as the high conversion efficiency,good beam quality and long lifetime,hence they have become a new generation of excellent coherent light sources and one of the most important research fields in laser technology.All-solid-state ultrashort-pulse lasers have wide applications in various fields of physics,biology,medicine,optical fiber communication and high-precision processing as a result of their excellent properties such as the ultra-short pulse widths,high peak power and high repetition rates.In this dissertation,picosecond pulsed lasers at 1064 nm was demonstrated by laser-diode(LD)end-pumped Nd:YV04 laser and passively mode-locked by SESAM,through intracavity frquency doubling by KTP crystals.The main contents are listed as follows:1)The history of all-solid-state laser and the development of mode-locking techniques were overviewed firstly.The mode-locked laser with high average output power,high peak power and ultra-high repetition rate was introduced.Its highlighted that ultra-short pulse laser has a superiority in the field of high-precision machining compared with the traditional machining.2)The principle of mode-locking was introduced.The formation of ultra-short laser pulse in passively mode-locked lasers was analyzed.The threshold formula for continuous mode-locked operation was obtained by deriving the rate equations.Besides,structural features of SESAM are summarized and both their advantages and disadvantages are analyzed.3)Both theoretical simulation and experimental research in 1064 nm passively mode-locked laser were performed.Before setting up the experimental system,the focal length of the crystal thermal lens under different pump spot sizes was calculated according to the crystal thermal effect theory.Then the beam transmission matrix was calculated through matlab programming,and the stable area range of the resonant cavity was obtained.The size of the spot in the cavity was optimized,and the initial parameters of the cavity were finally determined.In the experiment,a 1064 nm pulsed laser output with a maximum average power of 3.88 W,a pulse width of 8.172 ps,a repetition frequency of 147.1 MHz,and an optical-optical conversion efficiency of 32.3%was obtained.4)By using KTP as a frequency-doubling crystal,adopting an intracavity frequency multiplication structure,using the same four-mirror folded cavity and optimizing the parameters of the resonant cavity,a mode-locked green laser at 532 nm with average output power of 626 mW was obtained.The repetition is 132.3 MHz,which is in accordance with the theoretical calculations.