Microlens arrays of high-refractive-index glass fabricated by femtosecond laser lithography

• Published in: Applied surface science 2009-09, Vol.255 (24), p.9750-9753
• Main Authors: Nishiyama, Hiroaki, Nishii, Junji, Mizoshiri, Mizue, Hirata, Yoshinori
• Format: Article
• Language: English
• Subjects: 3D surfaces; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Femtosecond laser; Microlens; Micromachining; Physics
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2009.04.064

Microlens arrays of high-refractive-index glass GeO 2–SiO 2 were fabricated by femtosecond laser lithography assisted micromachining. GeO 2–SiO 2 thin glass films, which were deposited by plasma-enhanced chemical vapor deposition, have a refractive index of 1.4902 and exhibit high transparency at wavelengths longer than 320 nm. Using a femtosecond laser, three-dimensional patterns were written inside resists on GeO 2–SiO 2 films, and then the patterns were transferred to the underlying films by CHF 3 and O 2 plasma treatments. This combined process enabled us to obtain uniform microlens structures with a diameter of 38 μm. The heights of the transferred lenses were approximately one-quarter the height of the resist patterns, due to differences in the plasma etching rates between GeO 2–SiO 2 and the resist. The lens surfaces were smooth. When 632.8-nm-wavelength He–Ne laser light was normally coupled to the lenses, focal spots with a diameter of 3.0 μm were uniformly observed. The combined process was effective in fabricating three-dimensional surfaces of inorganic optical materials.