RESUMO
Although a reflective optical system can theoretically realize ideal optical designs, it is not always the optimal choice compared with a refractive one because of the difficulty in achieving high wavefront accuracy. A promising solution is to build reflective optical systems by mechanically assembling all the optical and structural components made of cordierite, which is a ceramic with a very low thermal expansion coefficient. Interferometric evaluations of an experimental product demonstrated that diffraction-limited performance in the visible wavelength was achieved and maintained even after cooling to 80 K. This new technique may be the most cost-effective method for utilizing reflective optical systems, especially for cryogenic applications.
RESUMO
An immersion grating composed of a transmissive material with a high refractive index (n>2) is a powerful device for high-resolution spectroscopy in the infrared region. Although the original idea is attributed to Fraunhofer about 200 years ago, an immersion grating with high diffraction efficiency has never been realized due to the difficulty in processing infrared crystals that are mostly brittle. While anisotropic etching is one successful method for fabricating a fine groove pattern on Si crystal, machining is necessary for realizing the ideal groove shape on any kind of infrared crystal. In this paper, we report the realization of the first, to the best of our knowledge, machined immersion grating made of single-crystal CdZnTe with a high diffraction efficiency that is almost identical to that theoretically predicted by rigorous coupled-wave analysis.
