Low line density, high efficiency, volume phase holographic gratings for the Extremely Large Telescope's HARMONI spectrograph

HARMONI 是极大望远镜 (ELT) 的首批光仪器之一。它是一种积分场摄谱仪（也称为高光谱成像仪），可同时获取天空二维视场中每个点的近红外波长光谱。与自适应光学系统相结合，HARMONI 能够通过 ELT 实现最高的空间分辨率。精致的空间分辨率，加上 ELT 巨大的收集面积，意味着 HARMONI 可以通过光谱详细研究微弱的物体，例如宇宙历史早期的遥远星系。我们希望通过进一步提高衍射光栅制造的最先进水平来增强 HARMONI 的能力。该提案的目标是扩展当前的制造技术，以生产低线密度、高吞吐量、高均匀性的体积相位全息光栅。在 HARMONI 中使用这些光栅将使仪器的瞬时波长覆盖范围增加两倍，使我们能够在单次观测中观察到更多来自天文目标的发射和吸收光谱线。这提高了我们的观测效率，充分利用了宝贵的望远镜时间，同时也使我们能够研究我们无法以连续方式观测到的时变现象。作为该提案的一部分，我们正在组装一个实验装置来量化这些新开发的光栅的性能，并进行测试以确保其在近红外波长下的均匀性和高吞吐量。该设置将可供英国所有学科的其他研究小组的研究人员使用，从而增强该国在物理和天文学方面的仪器能力。

HARMONI is one of the first-light instruments for the Extremely Large Telescope (ELT). It is an integral field spectrograph (also called hyper-spectral imager) that takes simultaneous spectra at near-infrared wavelengths of every point in a two-dimensional field of view on the sky. Coupled with an adaptive optics system, HARMONI is able to achieve the highest spatial resolution possible with the ELT. The exquisite spatial resolution, coupled with the huge collecting area of the ELT, means that HARMONI can spectroscopically study faint objects in detail, such as distant galaxies at early times in the history of the Universe.We are looking to enhance HARMONI's capability by furthering the state-of-the-art in the manufacture of diffraction gratings. The goal of this proposal is to extend current manufacturing techniques to produce low line density, high throughput, high uniformity, volume phase holographic gratings. Use of these gratings in HARMONI will increase the instantaneous wavelength coverage of the instrument by a factor of two, allowing us to observe many more emission and absorption spectral lines from astronomical targets in a single observation. This increases our observing efficiency, making best use of precious telescope time, but also allows us to study time variable phenomenon that we cannot observe in a sequential fashion. As part of this proposal, we are assembling an experimental set-up to quantify the performance of these newly developed gratings, testing to ensure their uniformity and high throughput at near-infrared wavelengths. The set-up will be available to researchers from other research groups in all disciplines across the U.K., thus enhancing the country's instrumentation capabilities for physics and astronomy.