A study on fabrication of BaMgF 4 thin film toward frequency-conversion device in UV/VUV region

Abstract

BaMgF 4 is a novel ferroelectric fluoride which is transparent in the wavelength regions from 125 nm to 1300 nm. Recently, the trial production of the frequency conversion device with BaMgF 4 single crystal was reported for the ultraviolet (UV) and vacuum ultraviolet (VUV) wavelength regions, but there has been a few report on it. The BaMgF 4 is very attractive ferroelectric crystal because it can be used as a quasi phase matching (QPM) device such as LiNbO 3 or LiTaO 3 . Nonlinear crystals have very large nonlinear coefficients generally, but these coefficients limited wavelength regions to use due to the birefringent phase matching, which limited to the wavelength from 573 nm to 5634 nm. Thus the QPM technique is attractive to fabricate frequency-conversion device in the UV/VUV region. In this study, we have purpose to fabricate BaMgF 4 hetero-epitaxial thin films toward frequency conversion devices. The optical-grade BaMgF 4 single crystal has been fabricated by Bridgman method. Rather we focus on fabrication of BaMgF 4 thin films by the precise and careful method of ion beam sputtering. It will be possible to fabricate also its waveguide structure under the vacuum-consistent process.