High-resolution, high-efficiency narrowband spectroscopy with an s-p-phased holographic grating in double pass

Abstract

High-resolution spectroscopy (R>50,000) in astronomy typically uses echelle-type spectrographs, which excel for exoplanet detection via radial velocity but compromise throughput for atmospheric characterization. We propose and test a novel method to achieve very high spectral resolution with significantly higher throughput within a limited bandpass using a tuned, high fringe-density volume phase holographic (VPH) grating in double pass. Using a wavelength-tunable laser, we measured the dispersion and diffraction efficiency of this setup, finding that our tested VPH grating reaches a diffraction-limited resolving power >140,000 in double pass with a peak diffraction efficiency of 79% for unpolarized light. Based on current manufacturing capabilities, we estimate double-pass diffraction efficiencies >50% with resolving powers >200,000 are achievable from visible to near-infrared wavelengths, limited only by detector size.