Simulation of Rowland ghosts generated by recently fabricated ultraviolet reflection gratings

We report on progress evaluating errors common in the fabrication of blazed reflection gratings for use in ultraviolet astronomy. Gratings studied are produced via electron beam lithography (EBL), nanoimprint lithography (NIL), and potassium hydroxide (KOH) wet-etching and are measured interferometrically. Fabrication errors which manifest as groove discontinuities are of particular interest as they cause “Rowland Ghosts,” or the appearance of a multiplicity of a single diffracted order due to error in the grating’s periodicity. This means that, though a grating may have high spectral resolution or high total efficiency, there is a blending of light from primary and ghost orders leading to an overall loss of information. Understanding the effect of these feature placement errors is critical to the characterization of how these gratings would behave when integrated into a spectrograph. We report on progress simulating the intensity distribution and Rowland Ghosts generated by real, imperfect, gratings fabricated via EBL, NIL, and KOH and measured interferometrically in an effort to understand each technique’s limitations and characterize their performance.