Laser Pulses In Silica Glass Research Articles

Ultrafast time-resolved single-shot birefringence microscopy for laser-induced anisotropy.

The interaction between ultrashort laser pulses and materials in the ultrafast time domain, especially regarding the effect of laser polarization, has attracted much attention. In this study, ultrafast time-resolved single-shot birefringence microscopy is performed to observe laser-induced anisotropy. The birefringences of the optical Kerr effect and laser-induced anisotropic nanostructures by femtosecond laser pulses in silica glass are measured, and their slow axis is confirmed to correspond to the linear polarization angle of the pump light. We discuss the time variations of these birefringences in the picosecond time domain.

Filamentation of ultrashort laser pulses in silica glass and KDP crystals: A comparative study

Ionizing 800-nm femtosecond laser pulses propagating in silica glass and in potassium dihydrogen phosphate (KDP) crystal are investigated by means of a unidirectional pulse propagation code. Filamentation in fused silica is compared with the self-channeling of light in KDP accounting for the presence of defect states and electron-hole dynamics. In KDP, laser pulses produce intense filaments with higher clamping intensities up to 200 TW/cm$^2$ and longer plasma channels with electron densities above $10^{16}$ cm$^{-3}$. Despite these differences, the propagation dynamics in silica and KDP are almost identical at equivalent ratios of input power over the critical power for self-focusing.

Acoustic monitoring of microplasma formation and filamentation of tightly focused femtosecond laser pulses in silica glass

Contact acoustic technique has been employed to perform spatially resolved in situ detection of microplasma formation and filamentation of tightly focused femtosecond laser pulses with supercritical pulse powers in bulk dielectrics, via corresponding acoustic emission. Investigation of acoustic generation mechanisms related to the plasma formation and filamentation effects reveals the critical character of the opaque microplasma and provides estimates of its gigapascal-level pressures and energy densities of a few kJ∕cm3. The acoustic measurement enables real-time in situ monitoring and revealing of basic mechanisms of ionization and filamentation in bulk dielectrics.

Quasi-soliton and multifocal propagation of high-intensity laser pulses in silica glass

The results of numerical simulation of propagation of high-intensity ultrashort pulses in silica glass are presented. It is shown that in the case of a dynamic balance between self-focusing and defocusing induced by ionisation, radiation propagating in the glass over the distance of the order of a diffraction length can be captured to form a quasi-soliton. For certain relations between the parameters of radiation and glass over lengths exceeding the diffraction length, the multifocal propagation regime is possible.

Wavelength division with three-dimensional couplers fabricated by filamentation of femtosecond laser pulses.

Refractive-index changes can be induced by filamentation of 800-nm, 1-kHz femtosecond laser pulses in silica glass. Two-dimensional translation of a 40-microm-long filament leads to the formation of a curved waveguide because of bending by the previously induced refractive-index change. The fabrication of 2-mm directional couplers to split the coupled beam into 1:1 at a wavelength of 632.8 nm is demonstrated. The realization of three-dimensional directional couplers and wavelength division in the output from the couplers is also demonstrated.

Volume Grating Induced by a Self-Trapped Long Filament of Femtosecond Laser Pulses in Silica Glass

A self-trapped filament of ultrashort laser pulses can induce a 10–500 µm-long region of refractive-index change in silica glass. The translation of filament perpendicular to the optical axis induces a layer of refractive-index change with a thickness of 2 µm. We stacked the layers periodically and fabricated volume gratings. We irradiated a He–Ne laser beam at the wavelength of 632.8 nm onto the gratings at the Bragg angle. The maximum diffraction efficiency was 74.8% with the grating that had the period of 3 µm and the thickness of 150 µm.

Anisotropic refractive-index change in silica glass induced by self-trapped filament of linearly polarized femtosecond laser pulses

Permanent refractive-index change can be induced by a self-trapped filament of intense ultrashort laser pulses in silica glass. We investigated the dependence of refractive-index change on polarization of incident laser pulses. As the region of refractive-index change can be selectively etched by hydrofluoric acid (HF), we first polished the sample and etched the cross section of the regions. The HF-etched cross section of refractive-index change that was induced by linearly polarized pulses was seen to be elliptical when observed with a scanning-electron microscope. By polarimetric analysis of diffraction from gratings fabricated by polarized ultrashort laser pulses, the index ellipsoid of refractive-index change was confirmed to be uniaxial and negative.

In situ observation of photoinduced refractive-index changes in filaments formed in glasses by femtosecond laser pulses

We investigated the relationship between the formation of filaments and local refractive-index changes induced by femtosecond laser pulses in silica glass. In situ observation revealed that the location of a filament coincided with that of the refractive-index change. Observation also showed that the region of refractive-index change was elongated toward the upstream direction of the laser pulses with increasing exposure time. The region of refractive-index change was several hundred micrometers long, and its diameter was smaller than 2 mum. The refractive-index change was confirmed by two of three different methods to be as large as 0.8 x 10(-2).