Time-resolved microscopy of femtosecond laser filaments in fused quartz

Detailed picture of continuous shape evolution of femtosecond laser pulse has been recorded directly in the process of filament formation in fused silica using time-resolved polarization microscopy with similar to 70 fs temporal resolution. The main stages of the pulse transformation (temporal self-compression and splitting, formation of conical wave) have been studied. The maximum temporal compression has been found to be achieved by the leading subpulse after the time splitting event. It was found that the Bessel zone of conical wave formation is shifted backwards from the pulse front. Sub-and superluminal propagation velocities of the pulse maxima after the time splitting have been measured

Femtosecond filamentation in chalcogenide glasses limited by two-photon absorption

Filamentation of 800 nm femtosecond laser pulses in the conditions of strong two-photon absorption was first directly observed in As4Ge30S66 chalcogenide glass, this effect being accompanied by increase in the pulse spectrum width from 8.5 to 11 nm and its modulation indicating the pulse temporal splitting. In contrast, there was no filamentation and pulse spectrum widening in stoichiometric As2S3 glass. The nonlinear figure of merit was shown to be as high as 0.5 and only similar to 0.1 in glassy As4Ge30S66 and As2S3, respectively

Spatio-temporal dynamics of femtosecond laser pulses at 1550 nm wavelength in crystal silicon

Spatio-temporal transformation of the femtosecond laser pulses at 1550 nm wavelength in c-Si is observed using the methods of time-resolved microscopy. The temporal dynamics of the pulse manifests itself both in widening of the frequency spectrum and in the change of on-axis time-width. It is shown, that along with Kerr effect, two-photon absorption also contributes to the temporal reshaping of the laser pulse. Despite the fact that absorption length for green light in c-Si is as small as 1 A mu m, generation of visible third harmonics was also observed in c-Si

Single-pulse femtosecond laser fabrication of concave microlens- and micromirror arrays in chalcohalide glass

International audienceThe diffraction-limited piano-concave microlens- and micromirror arrays were produced in chalcohalide glass of 65GeS(2)-25Ga(2)S(3)-10CsCl composition transparent from similar to 0.5 to 11 mu m. Only a single 200 fs laser pulse with 800 nm central wavelength is required to form microlens, which after metal coating becomes a concave micromirror. This process can serve as a basis for flexible technology to fabricate regular microlens and micromirror arrays for optotelecom applications, its performance being limited only by repetition rate of the laser pulses (typically 1000 microlenses per second)

The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography

It is well known that the alignment of liquid crystals (LCs) can be realised by rubbing or photoalignment technologies. Recently, nonlinear laser lithography (NLL) was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time, the usage of the NLL as a perspective method of the alignment of nematics was presented. By NLL, nanogrooves with about 0.92m period were formed on Ti layer. The nanostructured Ti layer (NSTL) was coated with oxidianiline-polyimide film with annealing of the polymer followed without any further processing. Aligning properties of NSTLs were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy (AE) of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal AE, obtained for pure NSTL, is comparable with photoalignment technology. It was found that the deposition of polyimide film on NSTL leads to the gain effect of the azimuthal AE. Also, atomic force microscopy(AFM) study of aligning surfaces was carried out

Optical Waveguides Written Deep Inside Silicon by Femtosecond Laser

Summary form only given. Photonic devices that can guide, transfer or modulate light are highly desired in electronics and integrated silicon photonics. Through the nonlinear processes taking place during ultrafast laser-material interaction, laser light can impart permanent refractive index change in the bulk of materials, and thus enables the fabrication of different optical elements inside the material. However, due to strong multi-photon absorption of Si resulting delocalization of the light by free carriers induced plasma defocusing, the subsurface Si modification with femtosecond laser was not realized so far [1, 2]. Here, we demonstrate optical waveguides written deep inside silicon with a 1.5-μm high repetition rate femtosecond laser. Due to pulse-to-pulse heat accumulation for high repetition rate laser, additional thermal lensing prevents delocalization of the light around focal point, allowing the modification. The laser with 2-μJ pulse energy, 350-fs pulse width, operating at 250 kHz focused in Si produces permanent modifications. The position of the focal point inside of the sample is accurately controlled with pumpprobe imaging during processing. Optical waveguides of ~20-μm diameter, and up to 5.5-mm elongation are fabricated by translating the beam focal position along the optical axis. The waveguides are characterized with a 1.5-μm continuous-wave laser, through optical shadow-graphy (Fig. 1 a-b, e) and direct light coupling (Fig.1 c-d, f). The measured refractive index change obtained by quantitative shadow-graphy is ~6×10 -4 . The numerical aperture of the waveguide measured from decoupled light is 0.05