McPherson has released a new vacuum ultraviolet spectral test system, VUV-STS. The system measures reflectance as a function of angle of incidence. It measures optical performance 'at wavelength' and can help determine optical constants. It uses special techniques for measuring non-polarised light and works in the 30 to 160nm wavelength region. Transmission can be measured too, although it is not appropriate for many materials at these wavelengths. Options exist to extend operation up to 300nm.
This new twist from McPherson helps users test materials, multilayers and coatings 'at wavelength' in applications like attosecond spectroscopy and HHG, optical design for space applications, wavelength calibration, and thin-film/coating technique design.
Light coming from a monochromator has partial and often variable polarised content. Deep UV and vacuum UV wavelengths present challenges whenever there is polarisation. Most laboratory polariser’s rely on crystalline wavelength transmission. Air spaced Rochon prism polariser’s built from magnesium fluoride work to wavelength short as 140nm. The VUV-STS solution is to measure samples in two perpendicular planes of incidence. Then average them to negate influence of specific polarisation on reflectance (Ip-Is)/(Ip+Is). Measuring in two planes allows us to check the opposite values for each. It finally presents the reflectance for non-polarised incident radiation. This technique can be used for any reflective, diffractive or transmitting sample.
The VUV-STS is a one metre grazing incidence monochromator efficiently coupled to a windowless hollow cathode light source. The sample chamber is mechanically stiff and mounted in widely spaced and well supported bearings. Samples can rotate in two incident planes while under vacuum. Not cycling vacuum improves the quality of measurements. Other features include low noise high gain scintillated photomultiplier detector and easy to use rotation setting and data acquisition software. The McPherson software is for instrument control and does not do film analysis or other post processing – just machine control and data acquisition.