Ultrafast laser-induced birefringence in various porosity silica glasses: from fused silica to aerogel

Abstract

We compare a femtosecond laser induced modification in silica matrices with three different degrees of porosity. In single pulse regime, the decrease of substrate density from fused silica to high-silica porous glass and to silica aerogel glass results in tenfold increase of laser affected region with the formation of a symmetric cavity surrounded by the compressed silica shell with pearl like structures. In multi-pulse regime, if the cavity produced by the first pulse is relatively large, the subsequent pulses do not cause further modifications. If not, the transition from void to the anisotropic structure with the optical axis oriented parallel to the incident polarization is observed. The maximum retardance value achieved in porous glass is twofold higher than in fused silica, and tenfold greater than in aerogel. The polarization sensitive structuring in porous glass by two pulses of ultrafast laser irradiation is demonstrated, as well as no observable stress is generated at any conditions.

Well-controlled femtosecond laser inscription of periodic void structures in porous glass for photonic applications

“…We note that for the solid material, another equation [18,23] can be derived based on the energy conservation law as follows: assuming that the internal energy of the material with volume of 4 3 πr 3 is around the absorbed laser pulse energy, one gets 4 3 πYr 3 0 ≈ E abs . The fact that voids grow only slightly with laser energy means that upon a certain laser energy above the densification threshold, the absorbed fraction is almost constant, whereas energy losses should grow linearly.…”

“…It was demonstrated, furthermore, that silica glasses with different densities including fused silica, porous glass, and aerogel could be also successfully processed [23,24]. For porous glasses, several regimes were identified [24] with different corresponding types of material modifications ranging from densification and microvoid formation to wider channels appearance.…”

“…Additionally, femtosecond laser-induced formation of nanopores and voids was investigated for the initially non-porous optical materials [3,[15][16][17]. Such effects as strong explosion and shock wave formation were shown to play a role in a single void formation for tightly focusing conditions [9,[18][19][20][21], whereas cavitation and nanopores were found to play a role in volume leading to nanograting formation when laser focusing was not so strong [17,22,23].…”

Form and magnetic birefringence in undulated Permalloy/PET films

“…For this purpose, various pulse laser durations, ranging from nano to femtosecond regimes, have been used to create ordered nanostructures in different systems, e.g. metals [4], dielectrics or semiconductors [1,5,6]. More recently, this research has been also extended to glasses [7,8] and different polymeric substrates [9][10][11][12].…”

Ultrafast laser induced nanostructured ITO for liquid crystal alignment and higher transparency electrodes

“…The patterned ITO electrodes are shown to be with higher transparency due the minimization of interface reflections; hence this methodology might find applications also in lowering the energy costs of optoelectronic devices. One of the most fascinating aspects of this technique is the ability to induce tunable structures with subwavelength periodicities at different orientations and so opens a new methodology to produce structured liquid crystal devices [18][19].…”