D. Le Coq

Mid-infrared astrophotonics: study of ultrafast laser induced index change in compatible materials

The mid-infrared wavelength regime 3.5 – 4.1μm, known as the astronomical L’ band is of special interest for exoplanet hunting. Mid-IR compatible photonic technologies are an enabling platform for a range of critical observational science using compact instruments on the next generation of Extremely Large Telescopes. Pupil remapping interferometry is a technique in which subapertures of the telescope pupil (2D) are reformatted into a 1D linear array. This can be done efficiently using 3D photonics. One of the most important techniques to fabricate 3D photonic devices in glass is ultrafast laser inscription. However, common silicate glasses are opaque above 2–2.2 μm and therefore not useful for the fabrication of waveguides at mid-infrared wavelengths. Here we present a study of mid-infrared transparent materials that are compatible with the ultrafast laser inscription technique. This study will inform the development of mid-infrared photonic devices for future exoplanetary discovery.

Laser filamentation in chalcogenide glass

We report laser filamentation in the bulk of chalcogenide glass with femtosecond laser pulses of energy on the nanojoule level. Spatially resolved measurements of the resulting refractive index modification are presented. The study of the pulse energy and focusing condition dependencies show that channels of positive refractive index variation of several millimeter length can easily be obtained.

Inscription of infrared waveguides in chalcogenide glasses by femtosecond laser

Waveguide inscription by femtosecond laser into a glass has a complicated dependence on writing conditions, laser parameters, and glass composition. In this presentation, we will firstly focus on a new method based on a helical translation of a chalcogenide glass sample through the focal point and parallel to the laser beam. This original technique based on an inscription characterized by a negative Δn, consists in a clad writing. Under these peculiar conditions, a high symmetry of the guided mode is achieved. Next, inscription by laser filamentation that leads to a positive Δn modification due to appropriated permanent structural modifications and new geometry of the infrared waveguides will be presented and discussed.

Zero-dimensional Cryogenic Glasses and Supercooled Liquids in the Se-Cl System

Raman spectroscopy and high-energy x-ray diffraction measurements of binary Se1−xClx glasses, supercooled and normal liquids have shown a gradual transformation of the chain-like one-dimensional (1D) structure of glassy selenium (x = 0) into a zero-D molecular structure of small non-linear and non-planar oligomeric molecules of SenCl2-type, where 2 ≤ n ≤ 5. Rapid cooling of the Se1−xClx liquids into liquid nitrogen yields transparent cryogenic glasses over the entire composition range, 0 ≤ x ≤ 0.5, whose glass transition decreases monotonically from 45°C to −70°C.

Structure of Te1−xClx Liquids

The structure of Te1−xClx. liquids having composition outside the glassy domain has been investigated using neutron diffraction. Te‐rich (x = 0.0, 0.1, 0.2, 0.3) and Cl‐rich (x = 0.7, 0.8) liquids have been measured just above their respective melting points, 240 °C⩽T⩽490 °C. The neutron structure factor SN(Q) exhibits a pronounced First Sharp Diffraction Peak (FSDP) for the Cl‐rich compositions suggesting a significant intermediate range order in these molecular liquids. In contrast, the FSDP appears to be weak for the Te‐rich liquid alloys presumably having a chain network structure. As expected, two different nearest‐neighbour distances have been found in the total correlation function TN(r). The first peak at r1≈2.4 A, corresponding to Cl‐Te contacts, increases with x. The second at r2≈2.8 A is related to the Te‐Te first neighbours and decreases with x. A detailed analysis of the TN(r) and difference ΔTN(r) is given in the contribution and allows between three possible structural models to be chosen.