Ultra-Broadband Laser Frequency Combs for Precision Spectrograph Calibration

天文学界面临的一个关键问题是如何为新的超高分辨率光谱仪提供永久在线校准，这在回答当今的“大问题”中发挥着核心作用，例如发现太阳系外的类地行星，以及“基本”常数的变化。自2007年左右以来，光子学界一直在与天文学家合作，以提供一种解决方案，其形式是一种超稳定的激光校准源，可以产生数千个规则间隔的光学频率的“梳”。由诺贝尔奖获得者霍尔和亨施开创的技术展示了如何稳定这样的梳，允许组成梳线的频率被冻结到接近1，000，000，000，000，000，000的精度（实际上比许多天文学背景下所需的水平更精确）。HIRES和ESTERO是E-ELT和VLT提出的高分辨率摄谱仪，它们的基础科学案例包括寻找类地系外行星、原始核合成和基本常数的可能变化。这两种仪器都需要出色的径向速度精度和稳定性（HIRES高达2 cm/s），这只能通过嵌入宽带激光频率梳形式的永久在线校准来实现。目前还没有一种激光频率梳技术能够完全提供必要的波长覆盖范围和模式间隔。此外，用于获得必要的波长覆盖和模式间隔的当前技术引入了伪像，其在部署在光谱仪上时破坏校准结果。因此，需要进行研究，以探索替代激光频率梳概念的可行性，以满足ESTERO和HIRES项目的需要。基于HWU独特的激光频率梳专业知识，并与HIRES和ESTEGO仪器的利益相关者合作，该项目将评估基于光学参量振荡器的宽带激光频率梳架构的几个新概念，并解决稳定性，均匀性，准确性和梳线间距的基本校准源标准。我们的主要工业合作伙伴Laser Quantum Ltd.将支持该项目的钛：蓝宝石泵浦激光器的高重复率，并与重要的技术诀窍。另一条开采路线是通过新的赫瑞瓦特分拆公司色度有限公司，该项目的成果将采取技术评估的形式，总结候选梳状架构的适用性，并展示最有前途的系统。

The astronomy community faces a critical problem in how to provide perpetual online calibration of new ultra-high-resolution spectrographs, which play a central role in answering today's "big questions" such as the discovery of extra-solar Earth-like planets, and the variation of "fundamental" constants. Since around 2007, the photonics community has been working with astronomers to provide a solution, in the form of an ultra-stable laser calibration source producing a "comb" of thousands of regularly spaced optical frequencies. Techniques pioneered by Nobel laureates Hall and Haensch showed how such a comb could be stabilised, allowing the constituent comb lines to be frozen in frequency to precisions approaching one part in 1,000,000,000,000,000,000 (actually a level rather more accurate than is needed in many astronomy contexts).HIRES and ESPRESSO are proposed high-resolution spectrographs at the E-ELT and VLT, respectively, whose underpinning science cases include the search for Earth-like exo-planets, primordial nucleosynthesis and the possible variation of fundamental constants. Both instruments demand exceptional radial velocity accuracy and stability, (up to 2 cm/s for HIRES), which can only be realized by embedding perpetual online calibration in the form of a broadband laser frequency comb.No laser frequency comb technology fully offering the necessary wavelength coverage and mode spacing has yet been demonstrated. Furthermore, the current techniques used to obtain the necessary wavelength coverage and mode spacings introduce artifacts which corrupt the calibration results when deployed on a spectrograph. Consequently research is needed to explore the feasibility of alternative laser frequency comb concepts which could meet the needs of the ESPRESSO and HIRES projects. Building on unique laser frequency comb expertise at HWU, and working with stakeholders in the HIRES and ESPRESSO instruments, this project will evaluate several new concepts for broadband laser frequency comb architectures based around optical parametric oscillators, and addressing the essential calibration-source criteria for stability, uniformity, accuracy and comb-line spacing.Engagement in the project by our principal industrial partner, Laser Quantum Ltd., will support the project with Ti:sapphire pump lasers of high repetition rate, and with vital technical know-how. A further exploitation route is provided via the new Heriot-Watt spin out company Chromacity Ltd., formed to commercialise Heriot-Watt's femtosecond OPO technology.Outcomes from the project will take the form of a technical assessment summarizing the suitability of the candidate comb architectures, and a demonstrator of the most promising system.