Prism coupling refractometry, a versatile and well-characterized technique, is a valuable tool for measuring the refractive index of transparent media in film or bulk forms. It offers distinct advantages over other refractometry methods as it does not require the same level of fabrication or user modeling of optical response. Our method, presented in combination with an infrared prism coupler, further enhances this technique. It not only allows for the measurement of optical constants but also significantly reduces the standard deviation previously found in this measurement. Furthermore, it enables the refractive index of these materials to be certified to the third decimal point or more, demonstrating the value and potential of this technique.
Prism coupling refractometry is an often-overlooked refractive index measurement technique. It is significantly different from other common refractometry techniques, as it does not require the complex geometry and costly sample fabrication associated with the minimum deviation method or interferometry, nor any assumptions about the material properties as in spectroscopic ellipsometry. Lastly, with proper calibration, it can be used to measure the index to the third or even fourth decimal place, out-performing most Kramers-Krönig-based methods. Here, we report on the design, construction, operating procedure, and data analysis for an infrared prism coupling refractometer and its implications on both work in the lab and as a common device for optical shop testing.
Advanced ceramics require well defined stoichiometries to exhibit their optimal electronic and optical behaviors. The CaS-La2S3 solid solution exhibits promising optical and thermoelectric properties but is also venerable to sulfur loss during processing. The characterization of this sulfur loss is difficult using traditional methods due to sample preparation, long acquisition times, and error bars which limit the usefulness of the measurement. In this paper, we show that our material system undergoes sulfur loss during processing and that this sulfur loss goes on to impact material physical properties. We access sulfur loss through the use of Raman spectroscopy and the evaluation of the full width at half maximum (FWHM) of the A1 peak of the system. We then correlate this Raman analysis and XRD to trends in the material properties as a function of sulfur loss.
Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF2, or AlF3) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF2 coupons made by ash evaporation of aluminum followed by resistive evaporation of MgF2. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV re ectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF2 mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.
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