| The Fe:ZnSe laser can generate high-energy and long-pulse,also repetitionfrequency and short-pulse mid-infrared coherent light for electro-optical countermeasure.However,there are a few reports on pulsed Fe:ZnSe laser under different pump wavelengths,pump repetition frequencies,pump pulse durations and working temperatures.Based on this,the long-pulse Fe:ZnSe laser with hundredmillijoule-level energy and hundred-microsecond-level pulse duration,and the gainswitched Fe:ZnSe laser with nanosecond-level pulse duration are studied theoretically and experimentally in this paper.In theory,the spectral characteristics and the variation of the upper level lifetime with temperature of the Fe:ZnSe crystal are analyzed,and the appropriate wavelength and pulse duration of the pump are hence determined.The thermal model of the endpumped Fe:ZnSe crystal is established.In the simulation of the single pulse pumping,the temperature distribution of the crystal at the end of the pump pulse is studied,and the influences of pump parameters on temperature distribution are also analyzed;In the simulation calculation of repetition-frequency-pulse pumping,the crystal temperatures in the ascending and descending processes under low repetition frequency and small duty cycle,also the crystal temperature distribution under high repetition frequency are studied.Based on the theory of energy level transition and the operation mechanism of the Fe:ZnSe laser,the four-energy-level rate equations for the long pulse and short pulse of gain switching are established.In the study of long-pulse rate equation,the photon density versus time is studied,and the factors affecting it are analyzed.In the study of the gain-switching rate equation,the build-up process of the laser pulse is studied,and the characteristics of population inversion density,maximum photon density,laser pulse build-up time and pulse duration are analysed.In the experiment,the long-pulse Fe:ZnSe laser pumped by the Cr,Er:YAG laser is studied.Based on the absorption spectrum of the Er:YAG and Cr,Er:YAG crystals,the power supply for xenon lamp is designed,and the single-shot Er:YAG,Cr,Er:YAG lasers pumped by xenon lamp are compared.Under the same experimental conditions,the threshold of the latter is reduced by 29.3%,and the slope efficiency is increased by 52.2%.The maximum single pulse energy,central wavelength and pulse duration of the Cr,Er:YAG laser are 1.41 J,2931.2 nm and hundred-microsecond level,respectively.Using the Cr,Er:YAG laser as the pump,the maximum output energy of the Fe:ZnSe laser is 197.6 m J with the optical-to-optical efficiency of 14.3% at liquid nitrogen temperature of 77 K.The laser pulse shape is similar to the pump,and the central wavelenth is 4037.4 nm with the linewidth of 122.0 nm.At room temperature of 298 K,the maximum output energy of the laser is only 3.5 m J with the optical-tooptical efficiency of 0.25%,and the pulse duration is 7.8 ?s.The central wavelength is 4509.6 nm with the linewidth of 171.5 nm.The experimental study of repetition-frequency gain-switched Fe:ZnSe laser is also carried out.To solve the problem of pump shortage near 3 ?m,the 1 k Hz ZGP OPO and 1 Hz Ho,Pr:LLF laser are designed.At room temperature,using ZGP OPO as the pump,the maximum output power of the Fe:ZnSe laser is 58 m W with the optical-to-optical efficiency of 20.7%.The spectral range is 4030.2?4593.6 nm,and the pulse duration at maximum output power is 2.7 ns,which is the shortest pulse duration of the Fe:ZnSe laser reported so far.The effects of the pump energy and cavity length on the pulse build-up time and pulse duration of the Fe:ZnSe laser are also studied.At 77 K,the maximum output power is 63 m W with the optical-to-optical efficiency of 25.2%.The spectral range is 3686.6?4088.6 nm,and the shortest pulse width is 34.4 ns.Using the Ho,Pr:LLF laser as the pump,the maximum single pulse energy of the Fe:ZnSe laser is 16.4 ?J with the optical-to-optical efficiency of 16.5%at 77 K,the central wavelength is 3957.4 nm and the shortest pulse width is 13.9 ns. |
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