Fe:ZnSe laser radiation transmission by hollow waveguide

A special type of Cyclic Olephin Polymer silver coated (COP/Ag) hollow waveguide was used for delivery of 4.45 μm laser radiation. This mid-infrared radiation having major signification in special lidar or spectroscopy applications was generated by new bulk Fe:ZnSe laser working at the room temperature in gain switched regime. The coherent pumping of Fe:ZnSe laser was performed by electro-optically Q-switched Er:YAG laser which wavelength (2.94 μm) corresponds to the maximum of Fe:ZnSe absorption peak. The Er:YAG laser energy and pulse-length used was 11 mJ and ~ 300 ns, respectively. The generated Fe:ZnSe laser output energy was reached 1.1 mJ with the pulse-length 240 ns. The aim of the presented project was to investigate the transmission possibility of 4.45 μm mid-infrared Fe:ZnSe radiation by the COP/Ag hollow glass waveguide. The inner waveguide diameter was 700 μm and length 103 cm. Midinfrared laser radiation was focused into the guidance protector by the CaF2 lens with the focal length 55 mm. After the coupling Fe:ZnSe radiation optimization, the maximum transmission of radiation through the waveguide reached 64%. The time evolution of the pulse was not changed by the delivery but the space structure is changing essentially. It follows from the radiation transport principle of the hollow waveguide. The bent waveguide transmission was also investigated and 60% was obtained. For the case of contact application the fused silica cap was performed. As conclude the compact delivery system for 4.45 μm mid-infrared radiation with the short 240 ns pulse length and transmitted power density 0.57 MW/cm2 was successfully investigated and it can be used for the applications.