Design and modeling of spectrographs with holographic gratings on freeform surfaces

Abstract

In the present paper we demonstrate the approach of using a holographic grating on a freeform surface for advanced spectrographs design. We discuss the surface and groove pattern description used for ray-tracing. Moreover, we present a general procedure of diffraction efficiency calculation, which accounts for the change of hologram recording and operation conditions across the surface. The primary application of this approach is the optical design of the POLLUX spectropolarimeter for the LUVOR mission project where a freeform holographic grating operates simultaneously as a cross-disperser and a camera with high resolution and high dispersion. The medium ultraviolet channel design of POLLUX is considered in detail as an example. Its resolving power reaches [126,000] in the region of 118.5-195 nm. Also, we show a possibility to use a similar element working in transmission to build an unobscured double-Schmidt spectrograph. The spectral resolving power reaches 4000 in the region 350-550 nm and remains stable along the slit.

Next Generation FUV Spectrographic Imaging for Heliophysics

“…In addition to increased sensitivity, GUVI+ could benefit from having a grating that produces less scattered light. There is new work being done on free form optics, including the production of free form blazed holographic gratings [16]. Such a grating could in principle be more efficient, less noisy, and more sharply focused on the detector.…”

Progress in the Preparation and Characterization of Convex Blazed Gratings for Hyper-Spectral Imaging Spectrometer: A Review

“…Yang T. et al [ 22 ] used a point-by-point design method to create a compact freeform grating reflection imaging spectrometer. Muslimov E. R. et al [ 23 ] made advanced spectrometers with holographic gratings on freeform surfaces. Moreau V. et al [ 24 ] introduced ELOIS and CHIMA [ 25 ], two new instruments made of all aluminum and based on freeform diffraction gratings (FFG: freeform grating).…”

Limiting Spectral Resolution of a Reflection Grating Made via Electron-Beam Lithography

“…Hence, a high-accuracy patterning technique flexible enough to produce (1) blazed (2) grating patterns with variable line spacing (VLS) over (3) large areas on (4) freeform optical surfaces is desirable. Several techniques promise a viable pathway towards meeting these requirements, including photolithography on freeform substrates (Muslimov et al (2018b)) and mechanical ruling using atomic force microscopy (Gleason et al (2017)). In this paper, we focus on grating manufacture via electron-beam lithography (EBL).…”