Development of high photon throughput, high spectral resolution spectrometers using holographic and Echelle diffraction gratings for high temperature plasmas*

Two single channel prototype spectrometers have been developed for photon starved applications in high temperature plasmas, where high photon throughput and high spectral resolution are required. The first spectrometer follows a conventional Czerny-Turner setup using lenses instead of mirrors, while the second one is based on a novel design that incorporates an Echelle diffraction grating in Littrow configuration. Both spectrometers have the same spectral resolution and utilize the same camera but use different focal lengths. While the Echelle spectrometer, operated at high orders of diffraction, achieves a high spectral resolution at moderate focal lengths  it lacks the flexible nature of the Czerny-Turner spectrometer as Echelle diffraction gratings have to be operated at their fixed Blaze angle. However, our study shows that the Echelle spectrometer offers improved photon throughput compared to the Czerny-Turner spectrometer and considering the same f-number. This proves that the Echelle approach has a product of photon throughput and spectral resolution, which makes it a very interesting concept for applications in fusion energy science.