Research On Pulsed And Multi-wavelength Characteristics Of Diode-pumped Cesium-vapor Laser

Diode-pumped alkali-vapor lasers(DPALs)have the advantages of both diode and gas lasers,such as high quantum-efficiency,large stimulated-emission cross-section,small refractive index perturbance,easy heat elimination and rich laser wavelength.DPALs can obtain near-infrared laser output with high efficiency,high power and high beam quality,which have important applications in industrial manufacturing,military,medical,scientific research and so on.In particular,high-power high-repetition-rate pulsed DPALs show wide application prospect to be used in laser communication,light detection and ranging systems(LIDARs),material processing,laser cleaning,and so on.Meanwhile,by frequency doubling or different energy level transitions,DPALs can output blue,near-infrared,mid-infrared,and even far-infrared laser,which is a novel approach to achieve high-power multi-wavelength laser synchronously and coaxially.However,compared with high-power continuous-wave(CW)DPALs,the development of pulsed and multi-wavelength DPALs are not mature.Against this backdrop,we will take Cs-vapor DPAL as the research object to study the pulsed modulation technology and multi-wavelength output characteristics.The main contents of this dissertation are as below:1.In the aspect of theoretical research,the theoretical model of DPALs is established based on rate equation and beam propagation equation.The model can be solved by finite difference method,and the CW and pulsed Cs-DPALs are simulated.For the CW Cs-DPAL,we explore how the output power,conversion efficiency,and beam quality of the Cs-DPAL are influenced by the pump power,pump wavelength and linewidth,buffer gas pressure,temperature of vapor cell,reflectivity of output mirror,window transmittance of vapor cell,waist radius and position of pump beam,and cavity length,and the optimum values of above parameters are obtained.For the pulsed Cs-DPAL,the output characteristics of pulsed pump and active modulated Cs-DPALs are analyzed.The results show that the high-peak-power pulsed laser can be obtained when the rise-time of pump light or switching time of modulated device are in the order of nanosecond.2.The characteristics of pulsed pump Cs-DPAL and the frequency doubling of Cs-DPAL are researched experimentally.Firstly,the experimental setup of laser diode(LD)end-pumped Cs-DPAL is built,and the performance of the CW Cs-DPAL is investigated with the CW pump.And then with the pulsed pump,the influence of duty cycle,pulsed width and working temperature on laser power and waveform is analyzed.The maximum average power of the pulsed laser is 1.27 W.However,due to the long rise-time of the pump pulse,the peak power of the pulse laser is only ~ 1.90 W,which is similar to the laser output power with CW pump.This result is consistent with the theoretical simulation.By adjusting the repetition rate and duty cycle of the pump,the maximum repetition rate and the minimum pulse width of the pulsed laser are 3.3 kHz and 52 ?s,respectively.On the basis of the above experiments,the experimental devices of intracavity frequency doubling of Cs-DPAL are set up to output blue laser at 447.19 nm.With the CW and pulsed pump,the CW blue laser with the highest power of 245 ?W and the pulsed blue laser with the highest power of 227 ?W are obtained.The maximum peak power of the pulsed blue laser was ~ 340 ?W,and the maximum repetition rate and the minimum pulse width are 3.3 kHz and 57 ?s,respectively.3.The performance of acousto-optically modulated pulsed Cs-DPAL is studied experimentally,and the experimental setup is firstly built.The characteristics of the CW Cs-DPAL was investigated,and the influence of linearly polarized acousto-optically modulator(AOM)and polarizing beam splitter(PBS)on laser output power and polarization ratio is analyzed.And then the rectangular signal was applied to modulate the AOM,the pulse laser was obtained with the maximum repetition rate of 1 MHz and the minimum pulse duration of 238 ns.The influence of the repetition rate and duty cycle of the rectangular signal on the average power,peak power and beam quality of the pulsed laser is studied.Because of the long switching time of AOM,the maximum peak power of the pulsed laser is ~ 1W,which is approximately the CW laser power when AOM is closed.This result accords with the theoretical simulation.Finally,the AOM is modulated by coded signal,and the coded pulsed laser characteristics of Cs-DPAL at different bit rates are researched.The maximum bit rate of the coded pulsed laser is 2 Mb/s.4.The multi-wavelength characteristics of LD pumping Cs vapor is investigated experimentally.Firstly,the energy level transition processes of cooperative up-conversion and multi-wavelength photons generation of Cs atoms are analyzed.Then,the experimental device of Cs vapor pumped by 852 nm LD is set up to realize multi-wavelength fluorescence output.The blue light at 455 nm and 459 nm,near-infrared light at 852 nm and 895 nm,mid-infrared light at 2.93 ?m,3.01 ?m,3.095 ?m,3.49 ?m and 3.61 ?m are obtained.Finally,the effects of the vapor cell operating temperature and the pump power density on the relative intensity of the blue light and the mid-infrared light are studied experimentally,and the threshold conditions of the blue light and the mid-infrared light are obtained.