PHYS Seminar: “Laser-induced refractive index and birefringence control in silicon with advanced spatial laser modulation”, Alperen Saltık, 10:30AM July 1 2024 (EN)

“Laser-induced refractive index and birefringence control in silicon with advanced spatial laser modulation”

by Alperen Saltık,
Bilkent University, Department of Physics.

Advisor: Asst. Prof. Onur Tokel

Date: 01/07/2024
Time: 10:30
Place: SA-240 Seminar Room

Abstract: Exploiting nonlinear laser interactions within materials offers unique capabilities for exerting control on the optical properties, which can then be converted into three-dimensional (3D) functionality [1]. Silicon (Si), a material critical for electronics, photonics, and photovoltaics technologies, was limited to surface applications until recently. Nanosecond laser pulses were used to create state-of-the-art optical elements, including lenses, gratings, waveguides and holograms deep within the wafer, without altering the surface [2]. This 3D fabrication paradigm has the potential for enabling previously impossible optical capabilities and further integration of photonics and electronics industries. Towards this goal, one needs optical characterization capabilities within the bulk, which can be leveraged for advanced photonic functionality. In this thesis, we developed novel methods for volumetric characterization, leading to the creation of the first wave-plate optics inside Si. We first built a phase microscope and developed an algorithm to enable phase imaging under general error sources and stringent experimental constraints [3]. The refractive index evaluation capability enabled us to discover a new optical effect, stress-induced birefringence within the bulk of Si [4]. We also developed an analytical model, which we combined with phase microscopy, to introduce the first laser-written wave plates to the bulk of Si [4]. Further, we explored new fabrication architectures with spatially-modulated lasers, using vortex, Airy and Bessel type beam profiles. Finally, we apply the phase imaging capability to characterize emerging Bessel-beam written structures [5].

[1] Gattass, R. R., & Mazur, E. (2008). Femtosecond laser micromachining in transparent materials. Nature photonics, 2(4), 219-225.
[2] Tokel, O., et al. “In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon.” Nature photonics 11.10 (2017): 639-645.
[3] Saltik, A., Saylan, S., & Tokel, O. (2024). Fourier-transform-only method for random phase shifting interferometry. Journal of Optics, 26(3), 035604.
[4] Saltik, A., & Tokel, O. (2024). Laser-written wave plates inside the silicon enabled by stress-induced birefringence. Optics Letters, 49(1), 49-52.
[5] Sabet, R. A., Ishraq, A., Saltik, A., & Tokel, O. Laser nanofabrication inside silicon with spatial beam modulation and anisotropic seeding, Nature Communications, accepted, (2024).

You are cordially invited.