Ultrafast laser-induced refractive index tuning inside GeSbSNa glasses for mid-IR applications

Area of Science:

• Materials Science
• Photonics
• Optics

Background:

• Femtosecond laser direct writing (FLDW) is crucial for 3D structuring in transparent materials for integrated photonics.
• Chalcogenide glasses are promising for mid-infrared (MIR) applications but remain underexplored for FLDW.

Purpose of the Study:

• Investigate the photo-response of sodium-doped GeSbS (GeSbSNa) glasses under femtosecond laser irradiation.
• Quantify refractive index changes and structural modifications induced by laser writing.
• Assess the potential of GeSbSNa glasses for MIR photonic integration.

Main Methods:

• Femtosecond laser direct writing (FLDW) was used to modify GeSbSNa glasses.
• Quantitative phase microscopy was employed to measure refractive index changes (Δn).
• Raman spectroscopy analyzed laser-induced structural reorganizations.
• Isochronal annealing evaluated thermal stability.

Main Results:

• Achieved phase shifts up to 62 radians and Δn exceeding 0.05, among the highest for chalcogenides.
• Observed laser-induced densification, evidenced by a shift from corner- to edge-sharing GeS₄ tetrahedra.
• Demonstrated moderate thermal stability of the laser-induced modifications.

Conclusions:

• GeSbSNa glasses show high photosensitivity to FLDW.
• The materials are suitable for MIR photonic integration requiring high photosensitivity and moderate thermal durability.
• Results provide a quantitative basis for material assessment in photonic applications.