Spherical VPH Gratings for Enhanced Spectrograph Design

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

Diffraction gratings are a fundamental component at the heart of many astronomical instruments that measure the distribution of light at different wavelengths. Such measurements carry tremendous diagnostic information about the chemical composition of astronomical objects, and the dynamics of their motion. A more efficient kind of grating, called the Volume Phase Holographic (VPH) grating, has recently been under development, and offers great promise for practical applications. Particularly compact and light-efficient optical designs are made possible if VPH gratings can be made on spherical surfaces. The proposal for which this award was made is a pathfinding attempt to perfect the techniques for fabricating VPH gratings on spherical surfaces. Current spectrographs typically accomplish spectral dispersion on planar wavefronts, and this drives the optical design to large and hence expensive instruments. The VPH technology promises high-quality diffraction gratings on concave or convex spherical surfaces, enabling alternative and more compact spectrograph designs such as those utilizing the well-known Offner relay. The designs enabled by VPH gratings can have fewer as well as smaller components, and in some cases less exotic material while delivering higher efficiency. With this award, a pathfinder concept spectrograph using commercial off-the-shelf optical components will be built with resolving power R~1000 over the wavelength range 380-790 nm, feeding a 2k detector. This pilot project will pave the way for more advanced spectrograph designs in the future, exploiting the power of VPH gratings. This project has substantial broader impacts in that it could enable dramatically reduced size and cost while maintaining high performance, for a wide variety of astronomical instrumentation. Students will be involved in most aspects of the work. Funding for this project is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.