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）的第一批轻型仪器之一。它是一个积分场摄谱仪（也称为超光谱成像仪），可以同时获取天空中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能够实现ELT的最高空间分辨率。ELT的空间分辨率高，收集面积大，这意味着HARMONI可以对微弱的物体进行详细的光谱研究，例如宇宙历史早期的遥远星系。我们希望通过进一步发展衍射光栅的制造技术来提高HARMONI的能力。本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，使我们能够在一次观测中观察到更多的天文目标的发射和吸收光谱线。这提高了我们的观察效率，充分利用了宝贵的望远镜时间，但也使我们能够研究无法以连续方式观察到的时变现象。作为该提案的一部分，我们正在组装一个实验装置，以量化这些新开发的光栅的性能，测试以确保其在近红外波长下的均匀性和高吞吐量。该设置将提供给来自英国所有学科的其他研究小组的研究人员，从而提高了该国在物理学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.