Preparation and transmission characteristics of a mid-infrared attenuated total reflection hollow waveguide based on a stainless steel capillary tube.

Stainless steel (SUS) capillary tubes were examined as a category of structural tube for establishing a metallic attenuated total reflection (ATR) GeO₂ hollow waveguide. GeO₂ films were grown on the inner wall of SUS tubes by different liquid phase deposition (LPD) cycles. Fourier transform infrared (FTIR) spectra, scanning electronic microscope (SEM) image, and transmission loss for a CO₂ laser were measured to investigate the effects of the LPD cycles on the transmission behavior of the hollow waveguide samples. The film thickness and surface roughness increase with every LPD cycle. The two LPD cycle sample has a film thickness equivalent to the CO₂ laser wavelength, while the surface roughness is acceptable. This sample has the lowest transmission loss (0.27  dB/m) among these samples. The bending loss, output beam profile, and full divergence angle (FDA) were further studied. Higher-order modes are excited by bending the sample, inducing additional loss, decentralized beam profile, and larger FDA.