We report on echelle gratings produced by diamond turning with groove spacings coarser than 20 lines per mm. Increasing the groove spacing of an echelle reduces the free spectral range allowing infrared orders to be matched to the detector size. Reflection echelle gratings designed for the near-infrared have potential wide application in both ambient temperature as well as cryogenic astronomical spectrographs. Diamond turned reflection echelle gratings are currently employed in space-based high-resolution spectrographs for 2 – 4 μm planetary spectroscopy. Using a sample diamond turned grating we investigate the suitability of a 15 line/mm R3 echelle for use in ground-based 1 – 5 μm spectroscopy. We find this grating suitable for 3 – 5 μm high signal-to-noise, high-resolution applications. Controlling wavefront errors by an additional factor of two would permit use at high-resolution in the 1.5 – 2.5 μm region.
In this paper we highlight the advances we have made in applying modern diamond-turning technology and techniques to the problem of manufacturing coarse-spaced echelon and echelle gratings for infrared spectroscopy-gratings with groove profiles and coarse line spacings that could not be produced using traditional ruling techniques. Diffraction gratings have been classified into three categories: echelons, echelettes, and echelles. What distinguishes these categories from one another are the gratings': line spacing, order of use, and the methods of manufacture. For example, echelles used in the visible and UV regions are ruled gratings, their grooves being formed to a specific "sawtooth" or blazed profile by a ruling process. In comparison echelons were not ruled gratings but an assembly of plane-parallel optical flats, stacked on one another to form a series of rectangular steps. By applying diamond-turning technology, Bach Research has been able to produce diamond-machined echelons and coarse echelles for use in far and near infrared spectroscopy. These gratings have line spacings from 7.5 to 0.25 mm and groove depths of 0.75 to 0.125 mm. These grooves are intentionally large with respect to the infrared wavelength of interest and were produced by machining directly into bulk-metal substrates. This was accomplished while maintaining the precision in spacing and "blazed" groove profile, so that the resulting grating had a diffracted wavefront quality of 0.7 waves RMS, in the 702nd order of 632.8 nm.
A novel pushbroom sensor concept is introduced which incorporates a faceted field-condensing mirror to image the same ground pixel simultaneously in several spectral bands, while eliminating temporal misregistration and MTF smear due to earth rotation. This paper presents an overview of the instrument concept and the fabrication and performance details for the mirror.
Ruled diffraction gratings and even holographic ones have a `surface texture' or an `inherent roughness' that is part of the grating making process. Using the new scanning probe microscopy (SPM), we can now see the structure that has been long suspected but not revealed using scanning electron microscopy. Also using the SPM, we can review the surface structure in the film prior to ruling as well as after. Gaining this experience, we have been able to make adjustments to the diamond tool and weight to improve the final products.
A need has arisen for efficient, blazed, symmetric gratings for use as beam splitters in far and extreme ultraviolet interferometers. In particular, the development of an all-reflection, far ultraviolet spatial heterodyne interferometer can benefit tremendously from such a grating. To fulfill this need, we have manufactured a mechanically ruled grating with a V-groove profile blazed for H Lyman-alpha at 1216 A. We present the grating performance at Lyman-alpha in the context of its application to the spatial heterodyne interferometer.