Ellipsometric Control of Laser Welded Materials

Abstract

The results of ellipsometric diagnostic of femtosecond laser welded fused silica-silica, fused silica-copper and fused silica-silicon samples are presented. The bonded interface of each sample is composed of numerous laser weld seams at their periphery in a closed shape pattern so as to seal the inner part due to optical contact of two species. The angular dependencies of ellipsometric parameters Δ and Ψ were obtained for the several areas of bonded interface of each sample, namely: laser weld seam at the periphery and laser sealing inner part. The parameter Δ abrupt changes in the vicinity of the Brewster’s angle ${{\upvarphi}}_{\text{B}}$ for the weld seam of the fused silica-silica sample while the dependence Δ(${{\upvarphi}}$) (${{\upvarphi}}$ is an angle of light incidence) for optical transmission window is characterized by smoother curve. The value of ${{\upvarphi}}_{\text{B}}$ for the weld seam is slightly less than the value ${{\upvarphi}}_{\text{B}}$ of optical transmission window for this sample by 0.2°. Such behavior of ellipsometric parameter Δ may be explained by the material modification inside glass due to femtosecond laser irradiation. This change is typically characterized by densification and caused by variation in the refractive index, and it may be also characterized by a strong birefringence inside the welded area.