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.

Adaptive Optics for astronomy has revolutionized the ground-based telescopes by providing the highest achievable image quality of the world. All the current 8/10m telescopes are progressively turned into adaptive telescopes, relying on complex AO systems integrated inside the telescope itself, and providing high-resolution images to the instrumentation downstream. The next step forward will come from the so-called Extremely Large Telescopes (ELTs), with facilities now providing 100% of their science assisted by AO. As a consequence, the astronomical community exposed to AO-corrected data is growing exponentially. However, the exceptional advancement in AO technology and observational capability has not been followed by a comparable advancement in the development of the associated data analysis methods. In particular, a critical point when analyzing AO data concerns the separation of the instrument contribution from the intrinsic signature of the astrophysical signal. This can only be achieved by an accurate estimation of the instrument Point Spread Function (PSF). An AO system increases the energy concentration of the PSF, but this latter suffers from a complex shape combining spatial, spectral and temporal variability. The main challenge for the AO PSF comes from the stochastic effects induced by the environment. The AO system partially compensates the aberrations induced by the atmosphere and the telescope, but the strength and spatial structure of the atmospheric turbulence is constantly evolving on time scales faster than seconds. In this context, deriving an accurate PSF model associated with every AO-observation remains a challenge, and the lack of PSF knowledge often represents the main limitation when analyzing AO data. Gains by factors 2 to 5 in science performance are achievable if accurate (%-level) PSF models would be available. Extracting the AO-PSF from the science images quickly fails for extragalactic fields that are usually empty of reference stars, or dense stellar fields for which crowding prevents the extraction of a single PSF. Moreover, the situation is particularly critical for integral Field Spectrographs (IFS), as their fields of view are generally too small to contain any point source that could act as PSF calibrator. When the PSF information cannot be properly extracted from the science image, an alternative approach is to predict the PSF shape based on auxiliary data. This is precisely the objective of APPLY, to provide the community with operational solutions for AO-PSF prediction, relevant to all conditions and all science cases. This is achieved thanks to (i) recent breakthroughs led by our group on AO-PSF modeling, (ii) taking advantage of innovative data processing methods and (iii) gathering a multidisciplinary team of astronomers, data specialists and AO experts. The major strength of APPLY relies in an integrated approach, where not only the PSF is provided, but the estimated PSFs are coupled with dedicated reduction tools and validated against “PSF science verification” observations. The optimization of the whole data-processing chain is carried-out with data processing specialists, and the quantitative scientific impact and critical feedback on the process is evaluated with astronomers. For that, the project takes advantage of access to large on-sky data-sets, as well as simulated data to demonstrate the pipeline accuracy in a controlled environment. The methodology is developed over three main Work Packages (WPs), dedicated to three major instruments: MUSE @ ESO-VLT, OSIRIS @ KECK and HARMONI @ ELT. But the methodology developed by APPLY is very general, and applications to other instruments will also be explored. By providing the predicted PSF with each single observation, we aim at impacting the largest community possible, and propose a new breakthrough toward the optimization of the scientific returns of AO observations.