Development of photonic technologies for astronomical instruments using ultrafast laser inscription

Recently there has been a desire to apply photonic concepts and technologies to astronomical applications, with the aim of replacing traditional bulk optic instruments. This astrophotonic approach is envisioned to produce compact devices that have the potential to provide the unprecedented precision and stability required for current astronomical goals, such as the detection of Earth-like exoplanets capable of supporting life. The work in this thesis covers the investigation of the technique of Ultrafast Laser Inscription (ULI) to create the building blocks that may lead to a fully integrated compact spectrograph for astronomy. Unlike conventional fabrication technologies, ULI allows custom three-dimensional optical devices to be directly inscribed within a bulk substrate. Volume gratings with high first order diffraction efficiencies optimised for a variety of wavelengths are demonstrated, with a view to providing efficient gratings for the midinfrared wavelength range. Initially the mid infrared transmitting material GLS was used to create gratings with a first order efficiency of 63 % up to a wavelength of 1.35 μm. Anti-reflection coatings were applied to GLS and gratings with an efficiency of 95 % at 1.02 μm were produced. A second material, IG2 was used and diffraction gratings with a first order efficiency of 63 % were produced, which were efficient up to a wavelength of 2.5 μm, with thicker gratings produced which have yet to be characterised in a mid-infrared setup. These developments show that practical mid-infrared volume gratings can be produced by the process of ULI. Photonic reformatters have also been developed to reshape a multimode telescope point spread function into a pseudo-slit, suitable as an input for a diffraction-limited spectrograph. Two device designs were investigated. The first was a fully integrated ULI component which, tested in the laboratory reformatted a multimode input at 1550 nm into a slit, single mode in one axis and highly multimode in the orthogonal axis with an efficiency of 66 %. The device was tested on-sky at the William Herschel Telescope and performed with an efficiency of 19.5 % over the wavelength range 1450 to 1610 nm. The second, improved device combined a ULI component with a multicore fibre component, and performed with a similar performance in the laboratory demonstrating an efficiency of 69 %, but a much improved on sky efficiency of 53 % showing a potential for such devices to be used as an input for a diffraction limited spectrograph

Optimisation of ultrafast laser assisted etching in fused silica

Observations of runout distances combined with velocity measurements suggest that “major” dry-mixed avalanches show a scale invariance to the total drop height HSC. This is in accordance to the proposed upper-limit envelope of the maximum velocity by McClung and Schaerer (2006). The observations are also supported by a simple scaling analysis using a simple mass block model on cycloidal and parabolic tracks (Gauer, 2018b), concluding Umax~ gHSC/2 . In this supplementary paper, a simple mass block model is presented that includes basic observations of major dry-mixed avalanches, such as mass entrainment and deposition, and that reflects this scale invariance. Almost all model parameters can principally be observed in the field. Model results are compared with a series of avalanche observations of runout and velocity and match well, considering that the model is a first order approximation

Efficient photonic reformatting of celestial light support data

Files containing individual waveguide measurements for the ULI reformatter chip, and on-sky images captured to determine hybrid reformatter throughput and performanc

Optimisation of ultrafast laser assisted etching in fused silica Selectivity Data

Numeric selectivity data used to generate Figures 4 and 5