Theoretical Study Of Upconversion Ultraviolet Laser In Pr～(3+):ZBLAN Fiber

To realize upconversion UV laser in laser medium, theoretical studies ofupconversion UV laser kinetics are necessary. In this thesis, we theoreticallystudy the feasibility of realizing upconversion UV laser in Pr³⁺: ZBLAN fiber.Firstly, by utilizing steady population rate equations and propagationequations, we investigate the kinetics of upconversion UV laser of Pr³⁺ inPr³⁺:ZBLAN。Two pump lasers input into the fiber. One laser pumps the groundstate manifold 3H4 into an intermediate manifold 1D2.And another pump laserexcites intermediate manifold 1D2 to the upper lasing manifold 1S0. And we know,there exist the population inversions between 1S0 state and the highest Stark levelof 3F4, 3F2 ,3H4 level. But we found it is possible only between 1S0 state and thehighest Stark level of 3F4 for laser oscillator, for the too small emit-cross of 3F2 or3H4 level.The threshold pump powers, output power, slope efficiency and optimumcavity length are calculated and discussed. In different Pr³⁺ concentrations, weobserved that the high concentration makes laser oscillator with low thresholdpump powers but high slope efficiency. The threshold pump powers increaselinearly with the fiber length increased. Short fiber cavity length is better for highslope efficiency, and the best slope efficiency can be more than 16.7%. Shortcavity length and low pump powers are disadvantage to the high output power.There exists a saturation pump power to obtain optimum output power when thefiber length is given. Given the characteristics of the laser, there exists anoptimum cavity length to obtain optimum output power.Secondly, we investigate the laser kinetics for upconversion UV in Pr³⁺:Ce³⁺:ZBLAN fiber. After two-step excitation for Pr³⁺ 4f5d state, energytransferring happens between Pr³⁺and Ce³⁺, then realizes laser transition fromCe³⁺ 5d state to the highest Stark level of 2F5/2 . And we studied two solutions forthe two-step excitation respectively, Ⅰis through intermediate manifold 1D2 andⅡ is through intermediate manifold 3P0 . As in model Ⅰ, it is known that , in thisfiber, the energy transferring happened,and outputted signal laser based on Ce³⁺5d state. But the threshold pump powers are high(more than 20W),slopeefficiency is low(less than 3%),and output power is low also(less than 0.2W).Because not all of the experiment parameters are come from ZBLAN fiber,itneeds further work for this research.In the same conditions, we compared these two laser system as bellow: ①Inboth system, threshold pump powers are high and more than 20W, but Ⅰis lowerthan Ⅱ;②T he optimum reflectivity R2 is about 80% in each system;③Slopeefficiency are low in these two laser system, when the fiber length and pumppowers are properly selected, slope efficiency tends to a optimum value, 3% insystemⅠ a nd 0.4% in system Ⅱ.④ The optimum cavity length is shorter than 1min each system.In conclusion, upconversion UV laser action is feasible to be realized inPr³⁺:ZBLAN fiber. But it's difficult to realize UV laser oscillator inPr³⁺:Ce³⁺:ZBLAN fiber, by energy transferring. This thesis provides theoreticalfoundation of realizing upconversion UV laser for Pr³⁺ in experiment.