| As a new type of gas laser,diode-pumped alkali vapor lasers(DPALs)possess the advantages of high quantum efficiency,low thermal effect,good beam quality,high-power CW operation,no hazardous expendable chemicals etc.,and have potential applications in laser cooling,material processing,directional energy transmission,medical,science and other fields.Therefore,in-depth study of kinetic and fluid dynamic processes,exploration of more powerful pumped configurations,prediction of the temperature distribution and output characteristics under high pump power are significant for future design of DPAL.In the dissertation,four new types of side-pumped configurations,including four-side,trapezoid,half-ring and ring LD pumping,are firstly presented.Compared to the previous pumped configurations,more pump LDAs are able to surround the cell for higher laser output.Different division methods of the cross-section of the vapor cell and the corresponding numerical approaches are proposed.According to the experimental parameters of a single,side pumped configuration,the outpt features of the four configurations are analysed.Secondly,under high power pumping,the high-energy-level transitions of alkali atoms(including energy pooling,photoexcitation,ionization and recombination etc.),amplified spontaneous emission and saturation effect should be considered,and flowing procedure should be employed.Combining the rate equations and the heat balance equation,a basic model of high-power pumped DPAL amplifier is established,and a simplified algorithm of temperature in the amplifying region is proposed.Then,the 3D temperature models of end-pumped DPAL amplifier and single-side and double-side pumped DPALs are presented.As well as the corresponding iterative algorithms of three-dimensional pump intensity,laser intensity and temperature are given.The calculation results show that under high power,the assumption that only a constant temperature or one-dimensional temperature distribution is considered is not sufficient,whereas the 3D model can achieve consistent results with the experiment Based on that,the 3D temperature distributions of the end-pumped amplifier and side-pumped laser are presented for the first time.Taking into account the radial distribution of pump and laser intensity,the axial distribution of pump and laser beam radius(together referred to as "beam distribution"),and the radial distribution of temperature,coupling the first-order ordinary differential equation(ODE)of powers and second-order ODE of temperature,the ODE models of DPAL and its amplifier is established.The calculation results show that in the gain medium the spontaneous emission area is hat-top,wider than the stimulated emission,which reduce the laser output to a certain extent.Additionally,the calculated heat production of quenching accounts for more than 50%,higher than that of relaxation.At last,comprehensively combining on the radial distribution of light intensity and the axial distribution of beam radius,as well as coupling the rate equations,power transmission equation and three-dimensional heat conduction equation,a physical model of time-dependent temperature in DPAL is established.The experimental and calculated dependences of power and temperature on time are in good agreement.And the measured average laser power and temperature rise are reproduced.For multi-pulse pumping,methods to shorter thermal relaxation time and enhance output energy are studied.The quasi-continuous-wave laser output is achieved with a laser repetition rate of more than 100 Hz,... |
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