Work

Processing Maps and Nano-IR Diagnostics of Type I Modifications in Mid-IR Germanate-Based Optical Glass

Year: 2026

Type: article

Abstract: Mid-IR flat/integrated optics require low-loss, programmable phase control. We investigate femtosecond laser direct writing (FLDW) in aluminogermanate glass (Corning 9754), first mapping the processing landscape to delineate no modification, Type I index increase, and spatial broadening regimes. We then operate in a non-accumulating regime that provides a broad, stable writing window. Quantitative-phase microscopy yields Δφ and a monotonic Δn with optically limited cross-sections compatible with low loss. Transmission spectroscopy shows high values (about 90% up to 4 µm) and no additional absorptions across the near-IR and mid-IR range. FTIR reveals a redshift of the Ge–O–(Ge/Al) stretching envelope from ≈1 µJ, correlating with the high Δn onset. s-SNOM at 925 cm−1 resolves the written line as reduced near-field amplitude and decreased phase, confirming a local complex permittivity change consistent with densification-driven Type I tracks. Together, these results define practical conditions for on-demand mid-IR flat/GRIN/Fresnel optics by FLDW in this commercial mid-IR transparent glass.

Source: Photonics

DOI: 10.3390/photonics13020197

Authors: Paul Mathieu, Nadezhda Shchedrina, Florence De La Barrière, Guillaume Druart, Matthieu Lancry

Institutions: Université Paris-Saclay, Office National d'Études et de Recherches Aérospatiales, Institut de Chimie Moléculaire et des Matériaux d'Orsay, Département Optique et Techniques Associées

Language: English

Topic: Laser Material Processing Techniques

Subfield: Computational Mechanics

Field: Engineering

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,896

Funders: Agence Nationale de la Recherche, Ministère de l'Education Nationale, de l'Enseignement Superieur et de la Recherche, Agence de l'innovation de Défense