Astrocomb development for the ELT: enhancing capability with a modern laser platform

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This proposal aims to secure capital funding needed to support the continued development of laser frequency comb (LFC) technologies at Heriot-Watt University, which are needed for ultra-precise calibration of spectrographs in the next generation of new telescopes, such as the ELT. Specifically, the equipment will support research on E-ELT PPRP grant ST/S001328/1 ("The UK ELT Programme") and consortium grant ST/V000403/1 ("Precision Astronomical Spectrographs using Single-Mode Photonic Technologies"). Heriot-Watt's LFC architecture is based around a single ultrafast Ti:sapphire laser. This laser produces "ultrafast" laser pulses with durations of around 30 femtoseconds and with a repetition frequency of 1 GHz. These pulses serve as the pump source for a number of beamlines for wavelength down-conversion, visible- and near-infrared broadband supercontinuum generation, Fabry-Pérot étalon comb filtering and comb metrology / delivery. For nearly ten years, our astrocomb development has been based around an open-box Ti:sapphire laser, with limited output power, and now requiring time-consuming maintenance and realignment. For these reasons it is now poorly suited to the increasingly complex downstream systems that we are developing as a Phase B pilot for the UK ELT programme and in other wider research exploring new, robust astrocomb configurations.This single-item equipment bid is for a modern replacement laser offering 50% greater power (allowing the beam to be split across a greater number of beamlines) in a sealed zero-maintenance unit. Not only will this laser dramatically increase our productivity by avoiding many cumulative weeks of maintenance, but it is identical to the unit which is currently our laser platform of choice for adoption in the ELT-HIRES calibration unit, which requires a sealed, zero-maintenance and fully automatable laser source.Our proposal meets the assessment criteria in the following ways:(A) Strategic value within the STFC programmeThe requested laser will directly enhance research and development of basic astrocomb technologies, that must be deployed in around 10 years' time on telescopes such as the ELT. The UK (Cambridge, Durham, UKATC, Heriot-Watt) has a significant strategic role in the Italian-led ELT-HIRES spectrograph development, on which an astrocomb is needed for ultra-precise wavelength calibration. This equipment request will ensure that the UK continues to play an important role in the hardware development for the calibration of the ELT-HIRES spectrograph.(B) TimelinessAs the letter of support from Laser Quantum (Novanta) confirms, the equipment can be commissioned by 31 March 2022 as required in the conditions of the grant. Notably, projects ST/S001328/1 and ST/V000403/1 will have lifetimes of between one and three years from this date, and so the equipment will have the potential to enhance and accelerate the research programmes supported by these grants.