CC BY
6*
ALT'23 The 30th International Conference on Advanced Laser Technologies
LS-O-2
Direct laser writing of high retardance structures in nanoporous glass
S.I. Stopkin1, A.S. Lipatiev1, S.S. Fedotov1, T.O. Lipatieva1, Yu.V. Mikhailov1, S.V. Lotarev2, V.N. Sigaev1
1-Mendeleev University of Chemical Technology, Miusskaya sq. 9, Moscow 125047, Russia
2- Independent Researcher
e-mail: [email protected]
Recent advances in femtosecond laser technology enables the possibility of space-selective nanostructuring of transparent materials due to nonlinear absorption mechanism. Tightly focused femtosecond laser pulses can induce nanoperiodical structures named as nanogratings with polarization-controlled form birefringence inside fused silica [1]. The possibility of precision control of the retardance and the slow axis orientation of birefringence paves the way to the fabrication of geometric phase optics [2] as well as polarization converters [3]. However, the formation of nanogratings in silica and other oxide glasses requires tens of laser pulses [1,4] and the search for novel birefringent structures which can be laser-induced by few laser pulses is still in progress. For example, recently, a new type of birefringent structures consisting of elongated nanopores or single nanoplanes were discovered in silica glass irradiated by femtosecond laser beam [3]. On the other hand, the rapid formation of the form birefringence by only 2-3 laser pulses was showed in high silica nanoporous glass (NPG) [5]. This paves the way to using the nanoporous glassy materials for the inscription of high retardance optical elements. In this work we study direct laser writing of phase elements in nanoporous glass.
We used the NPG glass samples, which synthesis was described previously [5] for laser writing experiments. For the inscription of phase elements in the form of squares 300x300 ^m, we used femtosecond regenerative amplifier Pharos SP operating at the wavelength of 1030 nm. The pulse energy was varied from 300 to 800 nJ, at constant pulse repetition rate and pulse duration of 200 kHz and 180 fs respectively. The laser beam was focused inside the NPG by aspheric lens (N.A.=0.16). Measurements of retardance of birefringence was performed on laser-inscribed squares by raster scanning at 2 mm/s speed and interline separation of 1 ^m. The birefringence dispersion of squares was estimated by means of the polarizing optical microscope Olympus BX51 equipped with CCD camera Olympus DP73, polarizers and the set of interference optical filters. Taking the birefringence dispersion into account, the value of retardance was calculated by spectroscopic method [6]. The fiber optic spectrometer Ocean Optics USB2000 connected to the microscope was used for registration of transmission spectra of birefringent squares which slow axis was oriented at 45° to parallel and crossed polarizers. The retardance dependency on laser pulse energy was derived by fitting the normalized transmission spectra. The higher the pulse energy, the higher the retardance of inscribed birefringent squares. It was shown that the retardance value can be as high as 908 nm. This allows the laser writing of single layer phase plate for NIR and Mid-IR lasers that is impossible in silica glass. Thus, NPG is a promising medium for the efficient fabrication of phase optical elements. The work was supported by Russian Science Foundation (grant 22-79-10231).
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[2] R. Drevinskas and P.G. Kazansky, High-performance geometric phase elements in silica glass, APL Photonics, 2(6), pp. 066104, (2017)
[3] Y. Lei et al., Ultrafast laser nanostructuring in transparent materials for beam shaping and data storage, Opt. Mater. Express, 12(9), pp. 3327-3355, (2022)
[4] S.S. Fedotov et al., Direct writing of birefringent elements by ultrafast laser nanostructuring in multicomponent glass, Appl. Phys. Lett., 108(7), pp. 071905, (2016)
[5] S.S. Fedotov et al., 3-bit writing of information in nanoporous glass by a single sub-microsecond burst of femtosecond pulses Opt. Lett., 43(4), pp. 851-854, (2018)
[6] A. Messaadi et al., Optical system for measuring the spectral retardance function in an extended range, J. Eur. Opt. Soc.-Rapid Publ., 12, pp. 1-9, (2016)
