Ultrashort-pulse laser calligraphy

Control of structural modifications inside silica glass by changing the front tilt of an ultrashort pulse is demonstrated, achieving a calligraphic style of laser writing. The phenomena of anisotropic bubble formation at the boundary of an irradiated region and modification transition from microscopic bubbles formation to self-assembled form birefringence are observed, and the physical mechanisms are discussed. The results provide the comprehensive evidence that the light beam with centrosymmetric intensity distribution can produce noncentrosymmetric material modifications

Femtosecond laser nanostructuring for high-topological charge vortex tweezers with continuously tunable orbital angular momentum

It is well known that the light carries linear and angular momentum that can be transferred to the irradiated objects. Angular momentum of the beam is comprised of spin angular momentum (SAM) and orbital angular momentum (OAM). SAM is associated to the beam's polarization and is always intrinsic. OAM comes from the azimuthal phase variations of the beam and can be both extrinsic and intrinsic. The beam with helical phase phi = l.Phi, where phi is phase, Phi is polar angle and l is positive or negative integer number, possesses well-defined OAM with l.h [1]. Such beams are often referred to as optical vortices and are exploited in optical tweezer experiments enabling the rotation of trapped particles. Changing the wavefront's helicity, also the geometry of the beam is changed. The higher is |l|, the larger is the diameter of the beam. In order to change the total angular momentum of the beam, either the shape of the beam or the photon density has to be changed. As a result, the experiments which require fixed beam size and intensity are limited to fixed OAM. Recently, we implemented optical tweezers with tunable angular momentum, there OAM could be changed from -1 to 1 by controlling ellipticity of the incident laser beam. Here we extend this technology and demonstrate the generation of optical vortices of high topological charge up to 100 (Fig. 1(a)-(i)) using femtosecond laser written polarization converters (the S-waveplate) [2]

Bleaching of sol-gel glass film with embedded gold nanoparticles by thermal poling

Gold clusters embedded in glass are expected to be hard to dissolve in the form of ions since gold is essentially a nonreactive metal. In spite of that, bleaching of Au-doped nanocomposite sol-gel glass film on a soda-lime glass substrate is demonstrated in which electric-field thermal poling is employed to effectively dissolve randomly distributed gold nanoparticles (15 nm in diameter) embedded in a low conductivity sol-gel glass film with a volume filling factor as small as 2.3%. The surface plasmon absorption band at 520 nm is suppressed in the region covered by the anodic electrode. The phenomenon is explained by the ionization of the gold nanoparticles and the redistribution of gold ions in the glass matrix due to the action of the extremely high electrostatic field locally developed during poling

Void-nanograting transition by ultrashort laser pulse irradiation in silica glass

The structural evolution from void modification to self-assembled nanogratings in fused silica is observed for moderate (NA > 0.4) focusing conditions. Void formation, appears before the geometrical focus after the initial few pulses and after subsequent irradiation, nanogratings gradually occur at the top of the induced structures. Nonlinear Schrödinger equation based simulations are conducted to simulate the laser fluence, intensity and electron density in the regions of modification. Comparing the experiment with simulations, the voids form due to cavitation in the regions where electron density exceeds 1020 cm-3 but is below critical. In this scenario, the energy absorption is insufficient to reach the critical electron density that was once assumed to occur in the regime of void formation and nanogratings, shedding light on the potential formation mechanism of nanogratings

Erratum: "Ultraviolet poling of pure fused silica by high-intensity femtosecond radiation" [Appl. Phys. Lett. 86, 071106 (2005)]

Erratu

Visible luminescence from hydrogenated amorphous silicon modified by femtosecond laser radiation

Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells

Controlling ultrafast laser writing in silica glass by pulse temporal contrast

Control of laser writing in transparent dielectrics using temporal contrast of light pulses is demonstrated. Anisotropic nanopores in silica glass are produced by high-contrast of 10^7 femtosecond Yb: KGW laser pulses rather than low-contrast of 10^3 Yb fiber laser pulses. Low-contrast pulses are useful for creating lamellar birefringent structures, possibly driven by quadrupole nonlinear current. The difference originates in the fiber laser storing third of its energy in a post-pulse of 200 ps duration. The absorption of this low-intensity fraction of the pulse by laser-induced transient defects with relatively long lifetime and low excitation energy, such as self-trapped holes, drastically changes the kinetics of energy deposition and type of material modification

Thermal poling of glass modified by femtosecond irradiation

Thermal poling of silica glass modified by femtosecond laser irradiation is demonstrated. Increase of second-harmonic generation in the irradiated regions is observed. This enhancement is interpreted in terms of structural modifications in silica glass that make the poling process more efficient. Evidence of a change in the distribution of the electrostatic field frozen in glass during poling is obtained. This technique is used for (2) grating fabrication