Investigation On Several Key Technologies Of Improving Output Power Of LD Pumped Pulsed Solid State Laser

Solid state lasers are widely used in the fields of industry,medical treatment,scientific research and national defense.The absorption spectrum of Neodymium doped material matches the output wavelength of laser diode（LD）,so it is suitable to use LD as its pump source.LD pumped neodymium doped solid-state laser has the advantages of high efficiency,compact structure and long working life,and it is a four-level system with low laser threshold.Improving the output power of solid-state laser by overcoming the limitation of thermal effect and producing short pulse laser through laser pulse technology have been the focuses of researchers.This thesis focuses on the technical limitations of LD pumped Nd:glass mode-locked femtosecond laser,LD pumped acousto-optic Q-switched Nd:YAG nanosecond laser and LD pumped semiconductor saturable absorber mirror（SESAM）passively Q-switched Nd:YVO₄ picosecond microchip laser.Several key technologies are proposed to break through these limitations and experimental researches are carried out in this thesis.The main research results of this thesis include the following parts:The rotary disk laser technology is proposed to break through the limitation of average output power of LD pumped Nd:glass mode-locked femtosecond laser.A Nd:glass disk with diameter of 15mm is used to produce high power femtosecond laser pulses,with an average power of 0.49w and a pulse width of 324fs.The average output power of LD pumped Nd:glass mode-locked femtosecond laser previously reported is generally less than0.13W.It is verified that the rotary disk technology can break through the limit of average output power of LD pumped Nd:glass mode-locked femtosecond laser.A Nd:glass disk with diameter of 50mm is employed to experimentally study the power scaling of high power rotary disk mode-locked femtosecond laser.The femtosecond pulses with an average output power of 1.8W are obtained,with a pulse width of 350fs,a repetition frequency of 28MHz,a single pulse energy of 64n J,and a peak power of 183kw.As far as we know,this is the highest average output power obtained from LD pumped Nd:glass femtosecond laser.By using Nd:glass disk with a large diameter,the average output power of the high power rotary Nd:glass disk mode-locked femtosecond laser is scaled.A low-cost"quasi rotating"mechanism is proposed to realize a water-cooled high power rotary laser,and it is realized mechanically.Using LD as the pump source,the continuous-wave output characteristics of the water-cooled rotating disk Nd:YAG laser based on the"quasi rotating"mechanism are experimentally studied.When the diameter of the pump spot is 1.5mm,the average output power of 60W of continuous-wave laser is obtained,and the conversion efficiency of optical to optical is 40%.And the acousto-optic Q-switches are inserted in the resonant cavity.When the diameter of pump spot is 3mm and the repetition frequency of Q-switching is 7k Hz,high-power nanosecond pulses are output,with an average output power of 27.8W,a pulse width of 290ns,a single pulse energy of4mJ and a corresponding peak power of 14kW.The water-cooled high power rotary solid-state laser based on the"quasi rotating"structure provides a possible low-cost technology prototype for breaking through the thermal effect limitation of nanosecond laser.By using a SESAM with modulation depth up to 40%,the shortest pulse of 43ps is obtained from a LD pumped Nd:YVO₄ with a thickness of 300μm Q-switched microchip laser,with a repetition frequency of 140kHz,a single pulse energy of 19n J,and the corresponding peak power of 442W.By using a SESAM with modulation depth of 24%,the shortest pulse of 60ps is obtained.Using the SESAM with high modulation depth is a feasible technology to break through the limitation of output pulse width of passively Q-switched picosecond microchip laser.The researches of this thesis are based on the LD pumped neodymium doped solid-state lasers.In order to improve the average output power of mode-locked femtosecond laser and acousto-optic Q-switched nanosecond laser and shorten the output pulse width of picosecond microchip laser passively Q-switched by SESAM,the key technologies are explored.Significant results have been achieved,which is significant to promote the development of LD pumped pulsed solid-state lasers.