Structural modification on silica glass surface induced by thermal poling for second harmonic generation

Area of Science:

• Materials Science
• Solid State Physics
• Spectroscopy

Background:

• Bulk Herasil silica glass exhibits second harmonic generation (SHG) after thermal poling.
• Surface structural modifications are crucial for understanding SHG in silica glass.

Purpose of the Study:

• To investigate the structural changes in Herasil silica glass surfaces induced by thermal poling.
• To correlate these structural modifications with second harmonic generation (SHG).
• To elucidate the role of network and defect alterations in the poling process.

Main Methods:

• O-K edge X-ray Absorption Near Edge Structure (XANES) spectroscopy was employed to analyze surface structure.
• Theoretical calculations using a full multiple scattering approach were performed on model silicon dioxide clusters.
• XANES spectra were analyzed at various stages of the thermal poling and depoling treatment.

Main Results:

• XANES spectroscopy revealed significant structural modifications on the glass surface due to thermal poling.
• These modifications involve the breaking of Si-O-Si bridging bonds within the silica network and defects.
• Thermal depoling led to the reformation of bridging bonds, but the initial unpoled structure was not recovered.

Conclusions:

• Thermal poling induces irreversible structural changes on the surface of Herasil silica glass.
• The observed structural modifications are directly linked to the generation and erasure of second harmonic generation (SHG).
• The study highlights the sensitivity of silica glass surface structure to thermal treatments and its impact on optical properties.