Research On The All-solid-state Sum-frequency Lasers Based On Intracavity-pumping Technique

Laser diode pumped solid state lasers （DPSSL） has already become one of themost important research fields, with great expectations in the development of laserswith high efficiency, high power and high operating stability. Combining with thenonlinear frequency conversion technology （including the nonlinear frequencydoubleing and sum-frequency）, DPSSL’s output wavelengh and application fieldshave been greatly expanded, promoting the development of laser technology.Relatively speaking, all-solid-state frequency-doubled laser technology is moremature, but all-solid-state sum-frequency laser technology, as a more effectivetechnique, contains great potential in promoting the development of DPSSL.Taking the all-solid-state sum-frequency laser as the main research content, thisarticle designed and verified a new sum-frequency laser based onintracavity-pumping technique. A808nm laser diode is used to pump the Nd:YVO₄crystal emitting at914nm, and the Yb:YAG crystal （or the second Nd:YVO₄crystal）laser emitting at1030nm （or1064nm） intracavity pumped at914nm. Intracavitysum-frequency mixing at914and1030nm （or1064nm） was then realized in a BIBOcrystal to reach the blue laser at484nm （or491nm）.In order to reduce the threshold pump power of the quasi-three-level laser andimprove the laser’s operation stability, this paper established the quasi-three-levelrate equation of the transition of914nm spectral line, and then discussed theaffection of several factors on lasing performance of the quasi-three-level system,including model-matching, resorption losses and mode competition. We think thedistribution of pumping energy inside crystals depends on the pump-mode size ratio.Then, due to the high power density characteristics of resonant cavity, this paperdemonstrate an intracavity-pumping technique, and present a model to describe thedynamic behavior of an intracavity-pumped quasi-three-level laser. The laser systemhas been optimized with respect to the reflectivity of the output mirror, single-passtransmission of Yb:YAG crystal and two basic frequency light spot ratio. By thestudying of the theory of sum-frequency mixing, this paper discussed the smallsignal approximation, and discussed the optimum focusing condition in the processof sum-frequency.Components unit of all-solid-state sum-frequency laser have been optimized bysimulation using Matlab. Here, the crystal length and dopant concentration ofNd:YVO₄and Yb:YAG were given. The optimum phase matching angle of BIBOfor914and1030nm wavelengths was calculated. Besides, the optimum range ofcurvature radius, cavity length, and crystal position of three different resonant cavity structure （linear, V-shaped and Z-shaped） is also given in this paper.The experimental setup is designed in order to test the operation theory ofall-Solid-state sum-frequency laser. We designed LD end-pumped914nm Nd:YVO₄laser, intracavity-pumped Yb:YAG （or Nd:YVO₄） laser and all-solid-statesum-frequency laser in there different resonant cavity structure, respectively. Werealized914nm and1030nm （or1064nm） output using a LD end-pumped Nd:YVO₄laser and a intracavity-pumped Yb:YAG （or Nd:YVO₄） laser, respectively. Then, ablue laser at484nm （or491nm） is obtained by914nm and1030nm （or1064nm）intracavity sum-frequency mixing. Although these results are satisfactory, theconversion efficiency and operation stability of lasers remains to be improved.