Roman A. Zakoldaev

Femtosecond laser-induced stress-free ultra-densification inside porous glass

Unusually high densification ≤26% was obtained without lateral residual stresses within the laser beam waist inside porous glass during its multi-shot femtosecond laser irradiation, which may induce in the glass the related high refractive index change ~0.1. Corresponding laser irradiation regimes, resulting in such ultra-densification, decompaction and voids inside the glass, were revealed as a function of laser pulse energy and scanning rate, and were discussed in terms of thermal and hydrodynamic processes in the silica network.

Laser-induced microplasma as a tool for microstructuring transparent media*

We have studied the properties of laser-induced microplasma (LIMP) emerging in the ablation of a strongly light-absorbing target in the regime of confinement of spatial plasma expansion. The LIMP particle temperature is shown to be higher in this case than in the free expansion. It is found that the amplitude of the pressure pulse in the regime of spatial LIMP confinement is an order of magnitude higher than in the open surface case. The feasibility of writing microstructures on transparent dielectrics with the use of LIMP is demonstrated: microlens arrays and different diffraction elements are made.

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

We report control possibilities over ultrafast laser-induced periodic void lines in porous glass. Instead of high intensity regime leading to filaments, multi-pulse irradiation with high repetition rate (500 kHz) and various writing speed is used here in a transverse geometry. The formation of a perfectly controlled periodic void structure is shown to rely on such parameters as laser energy per pulse and scanning speed. In particular, both the threshold energy required for this effect and the period of the fabricated void arrays are shown to rise linearly with the number of the applied laser pulses per spot, or with a decreasing writing speed. To explain these results, a thermodynamic analysis is performed. The obtained dependencies are correlated with linear energy losses, whereas the periodicity of the observed structures is attributed to a static energy source formation at the void location affecting both material density and laser energy absorption.

Laser Technologies in Micro-Optics. Part 2. Fabrication of Elements with a Three-Dimensional Profile

Recent research in the field of formation of a 3D profile of optical elements with the use of direct laser writing at various wavelengths and photolithographic technologies on the basis of photomasks fabricated by means of laser writing is reviewed. Typical characteristics of the relief, as well as advantages and drawbacks of the above-mentioned methods are considered.

Forming micro-optical elements of extended form in the bulk of porous glass plates sodden with glycerol water solution under the laser irradiation

In this report we have presented the results of forming waveguide structures in the bulk of porous glass (PG) plates soddened with water solutions of different concentrations of glycerol — substance with high polarizability under the laser irradiation of wavelength low absorbed by plate material. Chemical composition of the plate used in experiment was such: 94.73SiO2 – 4.97 B2O3 – 0.30 Na2O, with porosity δpg= 0.26 cm3/cm3 and average channel size 2÷4 nm. As the irradiation source the pulse fiber ytterbium laser with wavelength 1.07 um and with pulse duration ~100 ns and pulse frequency 10÷100 kHz was used. Waveguide structure forming was occurred while the PG plate was moving with velocity 2÷3 um/s relatively to the formed irradiation beam.