Experimental Study On Cr²⁺:ZnS Laser And Its Use As Saturable Absorber

As the booming of diode pumped2μm wavelength solid laser, it is widely used inlaser radar, remote sensing and medical industry etc.. This paper mainly focus on thelaser which can output continuous wave with the Cr²⁺:ZnS crystal as the gain mediumand its application in2μm lasers as saturable absorber, the study is divided intotheoretical study and practical one.Two main aspects exist in theory. First, study and analysis on the optical propertyand luminous mechanism of Cr²⁺:ZnS crystal and other materials with adulteration ofCr²⁺ionic which provides a foundation on the study of continuous light laser with theCr²⁺:ZnS crystal as the gain medium; second, a model of rate equation is got from theanalysis of the rate equation of the Cr²⁺:ZnS saturable absorber under the passively Q-switched laser which shows the formula of the peak power, pulse width, pulse energyand energy efficiency of Q-switched pulse. All the above gives instructions to the actualexperiments.Experiments covers two aspects. First is the experiment on the Cr²⁺:ZnS laser. Astudy on the Tm:YLF laser as a pump source of1.89μm is made aiming to know theimpact on the output power by different wavelength selection type and different outputcoupler transmittance, from the above an optimized output scheme and a max outputpower of30W and slope efficiency of more than40%are achieved. Then the selectedTm:YLF laser is used to pump the Cr²⁺:ZnS crystals and analyse the features of outputpower with different cavity length and get a max output power of1.06W. Second is theexperiment on the Cr²⁺:ZnS as saturable absorber, what’s more separate passively Q-switched experiments are conducted with Ho:YAG，Ho:YVO4and Ho:YLF lasers. Thewriter analysed the differences of pulse energy, pulse width and repetition frequencywhen the aturable absorber is in different positions with the pump power increasing. Asthe repetition frequency of the Ho:YAG laser is approximate10kHz, the maximumaverage power is16.6W, the min pulse width is about36ns, and the maximum energyof a single pulse reaches2.6mJ. The single pulse energy from the Ho:YVO4laser isabout0.2mJ, and min pulse width of19.5ns and average output power of4.6W can begot from the pulse signal with a maximum repetition frequency of about20kHz. TheHo:YLF laser provides a maximum pulse energy of1.74mJ and min. pulse width of13.4ns. As the repetition frequency is1.90kHz which is the maximum one, thecorresponding average power reaches4.0W.In the end, conclusion and analysis is made on the experiments and suggestions aregiven for existing problems and further study.