Abstract In this Letter, a multi-pass amplifier based on polycrystalline Fe:ZnSe element grown by the chemical vapor deposition (CVD) method and doped through diffusion technique is realized with output energy of more than 3 mJ at 4.5 μm. The crystal used in the experiment has external doping layers with peak Fe ions concentration of (1-2)х1019 сm−3 located on the surface and Fe ions diffusion depth of hundreds of microns. The crystal demonstrates small-signal gain per pass of 5.7 (corresponding to effective gain of 7.1 cm−1 taking into account 8 mm total length of the crystal) for short pump pulse (40-ns) under the optimal pump fluence of around 0.8 J/cm2 and upper-level lifetime of 670 ± 10 ns under moderate cooling to 7-8 °C, which makes such a crystal very attractive for mid-IR femtosecond multi-pass amplifiers and generators. Moreover, properties of the polycrystalline Fe:ZnSe elements grown by CVD and doped through diffusion and CVD methods with higher Fe ions concentration are also studied at different temperatures and compared with a single crystal element.

中文翻译：

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用于高功率飞秒中红外激光系统的多晶 Fe:ZnSe 晶体的放大特性

摘要 在本文中，基于通过化学气相沉积 (CVD) 方法生长并通过扩散技术掺杂的多晶 Fe:ZnSe 元素实现了多通道放大器，在 4.5 μm 处的输出能量超过 3 mJ。实验中使用的晶体具有外部掺杂层，其表面 Fe 离子浓度峰值为 (1-2)х1019 сm−3，Fe 离子扩散深度为数百微米。在大约 0.8 J 的最佳泵浦通量下，对于短泵浦脉冲 (40-ns)，晶体显示每次通过的小信号增益为 5.7（对应于 7.1 cm-1 的有效增益，考虑到晶体的总长度为 8 mm） /cm2 和 670 ± 10 ns 的上能级寿命在适度冷却至 7-8 °C 的情况下，这使得这种晶体对于中红外飞秒多通放大器和发生器非常有吸引力。而且，