Direct Comb-Line Measurement: A New Calibration Concept for Astronomical Spectrographs

直接梳线测量：天文摄谱仪的新校准概念

• 批准号: ST/X002845/1
• 负责人: Derryck Reid
• 金额: $ 4.69万
• 依托单位: Heriot-Watt University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FX002845%2F1
• 关键词: Direct; Comb; Line; Measurement; New

For decades, astronomers have used hollow-cathode lamps as calibration sources for the spectrographs in optical telescopes, but their limitations mean that the community is now turning to laser frequency combs (LFCs), which provide a sequence of ultra-narrow, drift-free, regularly spaced optical frequencies on a selectable multi-GHz grid.Supported by STFC, HWU is leading the development and deployment of LFCs on several fronts, with current funding from PPRP (ST/S001328/1) and consortium (ST/V000403/1) grants.This capital equipment request directly supports our consortium grant, ST/V000403/1, in which a key goal is to develop LFC-based concepts to extract the wavelength solution of an astronomical spectrograph i.e. its "pixel-to-wavelength" mapping.In ST/V000403/1 we have already developed a comb-line-resolving spectrograph to pilot absolute calibration ideas. Unlike a sealed commercial instrument, we can access the focal plane of this device and place a mask there to use it as a high-resolution spectral shaper, before the light is then directed to an astronomical spectrograph. We propose to achieve this using a high-resolution digital micromirror device (DMD) containing 4 million tiny (7.6 micron) digitally-addressable mirrors.This concept offers some exciting possibilities for conditioning the light sent to the astronomical spectrograph. The most radical of these is to isolate a SINGLE COMB MODE and measure its wavelength to high precision with a commercial wavemeter before injecting it into the astronomical spectrograph. Repeating this process for each order of the spectrograph gives a direct means of obtaining the wavelength solution of each order, unlike current methods which provide just one fiducial wavelength marker for the whole spectrum.Preliminary calculations and an experimental sensitivity check show that this idea should be entirely feasible. The concept removes the uncertainty of which exact comb mode is observed on each order of the spectrograph, a problem normally addressed only by resorting to secondary measurements with a hollow-cathode lamp, or using a complex single-frequency laser locked to the LFC.Further opportunities exist to use the shaper to provide full-spectrum dynamic-range control by selectively attenuating brighter parts of the comb, and to implement switchable comb-mode spacings by selectively removing every nth comb line.Specifically, two items of equipment are requested to construct a prototype spectral shaper (forming a single equipment item): 1. DMD and driver board (Vialux DLP SuperSpeed V-Module) @ £12,202 2. Precision wavemeter (High Finesse WS7-60) @ £26,130Both items have a value below the regulated procurement threshold of £50,000, so no tender process is required. Orders will be placed under a non-competitive action, because of the unique performance capabilities of each item.Lead times for both items are a maximum of 16 weeks, so both can be ordered, delivered and receipted within the lifetime of the capital equipment grant.Including VAT and a 20% contribution from Heriot-Watt University, the final cost to STFC is £36,799, making this a relatively low cost capital equipment request that could offer considerable value to the astronomy community by piloting a new digital calibration approach for astronomical spectrographs.

几十年来，天文学家一直使用空心阴极灯作为光学望远镜中摄谱仪的校准源，但其局限性意味着业界现在正在转向激光频率梳 (LFC)，它提供了一系列超窄、无漂移的光谱，在可选的多 GHz 网格上规则间隔的光学频率。在 STFC 的支持下，HWU 在多个方面领先 LFC 的开发和部署，目前的资金来自 PPRP (ST/S001328/1) 和财团 (ST/V000403/1) 赠款。此资本设备请求直接支持我们的财团赠款 ST/V000403/1，其中一个关键目标是开发基于 LFC 的概念来提取波长天文摄谱仪的解决方案，即“像素到波长”映射。在 ST/V000403/1 中，我们已经开发了一个梳状线分辨光谱仪来试验绝对校准想法，与密封的商业仪器不同，我们可以访问该设备的焦平面并在那里放置一个掩模，将其用作高分辨率光谱整形器，然后将光引导到该设备。我们建议使用包含 400 万个微小（7.6 微米）数字可寻址镜子的高分辨率数字微镜设备（DMD）来实现这一目标。这个概念为调节光谱提供了一些令人兴奋的可能性。其中最根本的方法是隔离单梳模式并使用商用波长计高精度测量其波长，然后将其注入天文摄谱仪的每个阶次，从而得到直接的结果。与当前仅为整个光谱提供一个基准波长标记的方法不同，这是一种获得每一级波长解的方法。初步计算和实验灵敏度检查表明，这一想法应该是完全可行的。这一概念消除了在光谱仪的每个阶上观察到哪种精确梳状模式的不确定性，这个问题通常只能通过使用空心阴极灯进行二次测量或使用锁定到 LFC 的复杂单频激光器来解决。更多机会存在使用整形器通过选择性地衰减梳的较亮部分来提供全频谱动态范围控制，并通过选择性地去除每条梳线来实现可切换的梳模式间隔。具体来说，构建原型光谱整形器需要两项设备（形成单个设备项）： 1. DMD 和驱动板（Vialux DLP SuperSpeed V-Module）@ £12,202 2. 精密波长计（High Finesse WS7-60） @ £ 26,130 两件商品的价值均低于 50,000 英镑的监管采购门槛，因此无需进行招标。非竞争行为，因为每个项目都有独特的性能。这两个项目的交货时间最长为 16 周，因此两者都可以在资本设备补助金的使用寿命内订购、交付和接收。包括增值税和 20 % 赫瑞瓦特大学的贡献，STFC 的最终成本为 36,799 英镑，这使得这是一个成本相对较低的资本设备需求，可以通过试验一种新的天文数字校准方法为天文学界提供可观的价值光谱仪。