Transmission volume phase holographic gratings in photo-thermo-refractive glass written with femtosecond laser Bessel beams

• Published in: Optical materials express Vol. 6; no. 11; pp. 3491 - 3499
• Main Authors: Zhang, Y. J., Zhang, G. D., Chen, C. L., Stoian, R., Cheng, G. H.
• Format: Journal Article
• Language: English
• Published: OSA pub 01-11-2016
• Subjects: Beams (radiation); Diffraction efficiency; Diffraction gratings; Engineering Sciences; Femtosecond; Glass; Gratings (spectra); Heat treatment; Nanocrystals; Optics; Photonic; laser fabrication
• ISSN: 2159-3930; 2159-3930
• DOI: 10.1364/OME.6.003491

Transmission volume phase holographic gratings were fabricated in bulk photo-thermo-refractive glass using zero-order femtosecond laser Bessel beams and subsequent thermal treatment. Microstructures composed of nano-sized crystals were observed in the exposed regions. The concentration of nano-crystals depended on the writing power, but the size of the nano-crystals was found to be quasi power-independent. Low writing power led to sparse nano-crystals, while optimized writing power achieved dense nano-crystals distribution and high refractive index change. Effects of the gratings thickness, writing laser power and thermal treatment on the diffraction efficiency were investigated. A maximum diffraction efficiency of 94.73% was achieved (at 532 nm testing wavelength) with 1 mm grating thickness at period of 5 [mu]m.