Peter G. Kazansky

Fabrication of long-period fiber gratings by focused irradiation of infrared femtosecond laser pulses

We have fabricated long-period fiber gratings by use of a novel technique using focused irradiation of infrared femtosecond laser pulses. We investigate the thermal stability of the fabricated fiber gratings. The values of the loss peak wavelength and the transmittance of the fiber gratings after heat treatment below 500 degrees C are the same as initial values before heat treatment. The fiber gratings that were fabricated by this technique have a high resistance to thermal decay. We propose that this technique will be useful for fabrication of fiber gratings with a superior aging characteristic.

Radially polarized optical vortex converter created by femtosecond laser nanostructuring of glass

We demonstrate the generation of optical vortices with radial or azimuthal polarization using a space variant polarization converter, fabricated by femtosecond laser writing of self-assembled nanostructures in silica glass. Manipulation of the induced form birefringence is achieved by controlling writing parameters, in particular, the polarization azimuth of the writing beam. The fabricated converter allows switching from radial to azimuthal polarization by controlling the handedness of incident circular polarization.

Form birefringence and negative index change created by femtosecond direct writing in transparent materials

Although femtosecond lasers have proved to be of great utility for micromachining within bulk transparent materials, little is known about the fundamental physics that drive the process. Depending on the laser intensity delivered to the sample, any of three types of feature can be written into the glass. We observed that in the intermediate regime there is a correlation among the negative sign of the effective index change, the presence of anisotropic reflection, and birefringence. We propose a model that can explain all three principal characteristics. Results show that the local index change can be as high as 10(-1).

“Quill” writing with ultrashort light pulses in transparent materials

A remarkable phenomenon in ultrafast laser processing of transparent materials, in particular, silica glass, manifested as a change in material modification by reversing the writing direction is observed. The effect resembles writing with a quill pen and is interpreted in terms of anisotropic trapping of electron plasma by a tilted front of the ultrashort laser pulse along the writing direction.

Thermally poled glass: frozen-in electric field or oriented dipoles?

Evidence that a frozen-in space charge field causes the appearance of high quadratic nonlinearities in thermally poled glass is obtained from experimental tests of the ratio of nonlinear tensor components and the spatial distribution of the induced chi(2). A mechanism to explain the fixation of the chi(2) near the anodic surface is proposed.

High second-order nonlinearities in poled silicate fibers.

Effective quadratic nonlinearities as high as 0.2 pm/V are reported for the first time to our knowledge in poled germanosilicate fibers. This value is ~200 times higher than previously achieved in these fibers. The presence of Ge is found to enhance the efficacy of both thermal (in combination with OH doping) and electron-beam poling in silica.

Polarization sensitive elements fabricated by femtosecond laser nanostructuring of glass [Invited]

We review recent progress in application of femtosecond laser nanostructuring of fused silica. The tight control of nanostructures’ properties through writing parameters is demonstrated implementing elements with unique optical properties, which can be widely used in material processing, microscopy, optical trapping and manipulation.

Ultrafast Manipulation of Self-Assembled Form Birefringence in Glass

Ultrashort pulse lasers have allowed probing of molecular dynamics in real time on the femtosecond time scale, with exotic behavior ranging from alignment of molecules and clusters, structural deformation, phase transitions on solid, and electron localization in magnetic materials. A recent progress in high power ultrashort pulse lasers has opened new frontiers in physics and technology of light-matter interactions from X-ray generation, nuclear fusion, laser surgery, integrated and fiber optics, optical data storage, to 3D micro- and nano-structuring. An intriguing phenomenon that currently attracts a lot of interest is the self-assembly of periodic nanostructures in the direction perpendicular to the light polarization. Uniaxial birefringence observed after femtosecond laser irradiation of silica glass has been explained by induced nanogratings and referred as self-assembled form birefringence. Self organization process has been interpreted in terms of the interference of electron plasma waves resulting in electron concentration modulation, followed by freezing of the interference pattern by structural change in glass. However, the mechanism including dynamics of self-organized nanostructures formation is still not fully understood. Recently, a double-pulse pump-probe configuration was used to enhance ablation in fused silica and silicon. In similar experiments molecular ensembles with an oriented angular momentum were produced. Here, we describe the ultrafast writing dynamics of form birefringence produced by self-organized nanogratings in double pulse experiments. Rewritable five-dimensional (5D) optical data storage using self-assembled form birefringence was demonstrated.

High second-order nonlinearities induced in lead silicate glass by electron-beam irradiation

A new technique for inducing a large permanent second-order susceptibility in lead silicate glass is reported. The procedure involves implanting electrons by irradiating the glass with an electron beam. Second-order nonlinearities chi((2)) as high as 0.7 pm/V are obtained.

Birefringent Fresnel zone plates in silica fabricated by femtosecond laser machining

We demonstrate maskless, single-step fabrication of strongly birefringent Fresnel zone plates by focusing of femtosecond laser pulses deep within silica substrates. The process allows us to produce alternate zone rings directly by inducing a local refractive-index modification of the order of n~10(-2) . The embedded zone plates shown in this Letter exhibit efficiencies that vary by as much as a factor of ~6 for orthogonal polarizations. Focal lengths of primary and secondary foci are shown to compare well with theory.