Anatomy of a femtosecond laser processed silica waveguide [Invited]

Femtosecond versus picosecond laser machining of nano-gratings and micro-channels in silica glass

“…A second periodicity, Λ ~λ/n ~733 nm, apparently increasing as we move away from the tip of the structure is observed along the horizontal direction. Note that on this SEM image of the cleaved laser track, the irradiated zone seems to protrude out of the plane which is consistent with the volume expansion in the nanogratings zones [4,20,21]. The form-birefringence associated with nanogratings implies that the fabrication of polarization mode converters and spatially variant phase plates is possible even in this long pulse regime [12].…”

Compact Birefringent Waveplates Photo-Induced in Silica by Femtosecond Laser

“…This was the first time that quasi-periodic sub-wavelength structures made up by the light were fabricated in volume, in contrast to 2D nanogratings produced by lasers on surfaces [8]. Recently, we showed that these nanogratings consist of thin regions with a low refractive index (typically Δn = −0.15) due to volume expansion and the formation of nanoporous silica [5,6], surrounded by homogeneous regions with a positive index change. These porous nanolayers exhibit strong uniaxial negative form birefringence (typically ~10 −2 ) with a fast axis parallel to the polarization of the writing laser [9] and essentially arise as a result of condensation of vaporized glass within a confined but inflated volume after excitation.…”

“…Recently, further unique properties of laser induced glass modifications have been discovered including orientational dependent writing [2][3][4], glass decomposition [5,6] and elemental distribution with sub-wavelength spatial resolution [7]. To our knowledge, no other technique holds the same potential for realizing 3D multi-functional photonic devices fabricated in a single step in a wide variety of transparent materials, particularly high temperature silica.…”

Exciton mediated self-organization in glass driven by ultrashort light pulses

“…17 Excitons generated by subsequently arriving pulses of light are accumulated in significant concentrations in the specific sites of the sample corresponding to the peaks of the excitonpolariton density in the polariton grating that is generated in the same fashion by all pulses. Recombination of selftrapped excitons is accompanied by generation of molecular oxygen 26,27 due to the photosynthesis-like reaction,…”

“…Nanopores of silica filled by oxygen 27 are formed in the locations of high concentrations of self-trapped excitons. Formation of pores in fused silica was recently confirmed by another group investigating volume expansion induced by femtosecond laser irradiation.…”