V. Albanis

Nanosecond dynamics of a gallium mirror's light-induced reflectivity change

Transient pump-probe optical reflectivity measurements of the nano- to microsecond dynamics of a fully reversible, light-induced, surface-assisted metallization of gallium interfaced with silica are reported. The metallization leads to a considerable increase in the interface’s reflectivity when solid a-gallium is on the verge of melting. The reflectivity change was found to be a cumulative effect that grows with light intensity and pulse duration. The reflectivity relaxes back to that of a-gallium when the excitation is withdrawn in a time that increases critically at gallium’s melting point. It is shown that thermal processes cannot account for the effect and so a mechanism based on a nonthermal light-induced structural phase transition is proposed. DOI: 10.1103/PhysRevB.63.165207

Cross-wavelength all-optical switching using nonlinearity of liquefying gallium

The gallium/silica interface optical nonlinearity associated with a light-induced structural phase transition from a-gallium to a more reflective, more metallic phase shows an exceptionally broadband spectral response. It allows 40% deep nanosecond/microsecond cross-wavelength intensity modulation between signals at 1.3 and 1.55aem.

Femtosecond cubic optical nonlinearity of thin nickel films

Transient pump-probe measurements of circular anisotropy in nickel films induced by 38-fs optical pulses show an instantaneous response that is related to the optical orientation of the spins of free electrons. Measurements in a sample of variable thickness, performed in both transmission and reflection, revealed that the surface significantly influences the degenerate cubic optical nonlinearity of the nickel films to a depth of approximately 4-5 nm into the bulk.

Direct grating writing as a characterization technique for direct UV written waveguide structures

We use the Direct Grating Writing technique, based on Direct UV writing to define Bragg channel waveguides, investigating the relationship between the properties of the glass, the writing conditions, and the strength of the waveguide.

Light-induced specular-reflectivity suppression at a gallium/silica interface.

The reflectivity of a gallium/silica interface formed on an optical flat or at the tip of a cleaved optical fiber can be reduced in a reversible fashion when the interface is excited by a few milliwatts of laser power. This phenomenon occurs at temperatures just below galliums melting point. We believe that the effect can be attributed to light-induced structuring at the interface.

Directly UV-written planar channel waveguides containing simultaneously defined Bragg gratings

A new technique for the simultaneous writing of channels and Bragg gratings uses interfering focused UV beams in a photosensitive silica layer and is able to fabricate near-ideal Bragg gratings, with 60% reflectivity.

Single-step definition of channel waveguides with integral Bragg gratings in germanosilica-on-silicon wafers by direct UV writing

We present a single-step technique for defining channel waveguides with internal Bragg gratings in photosensitive germanosilica-on-silicon using two interfering focussed UV beams. Early devices exhibit reflection intensities of 80% with <0.15 nm bandwidth.

Light-induced reflectivity switching in gallium-on-silica films in the blue–green spectral region

The dynamics of the light-induced, reflectivity switching at a silica–gallium interface prepared by ultrafast pulsed laser deposition, is studied for the first time in the blue–green spectral region. A considerable interface reflectivity increase is seen at fluencies of about 1 mJ/cm2. The effect peaks at temperatures just below the gallium melting point (29.8 °C), while the reflectivity recovery times increase critically.

Dynamics of the light-induced structural phase transition in confining gallium and associated gigantic optical nonlinearity

Summary form only given. We report on a study of the nanosecond dynamics of a recently discovered light-induced, surface-assisted structural phase transition from a common orthorhombic phase of /spl alpha/-gallium to a highly reflective phase. The transition has been observed at temperatures just below the metals bulk melting point (30/spl deg/C). It is fully reversible with dynamics occurring on a nanosecond/microsecond time scale and can be stimulated by radiation of a very low intensity, typically 10/sup -4/-10/sup -5/ W//spl mu/m/sup 2/. The two gallium phases involved in the transition have significantly different optical properties which gives rise to a gigantic optical nonlinearity, /spl chi//sup (3)//spl sim/1 esu offering tremendous new opportunities in controlling light with light.

Gigantic broadband optical nonlinearity in gallium films deposited by ultrafast laser ablation

Gallium-silica interfaces have emerged as a new type of structure that combines a strong nonlinearity with picosecond switching-on time. Here we report that the optical nonlinearity of gallium films deposited on fused silica by ultrafast pulsed laser ablation is very broadband, spanning from 480 nm to 810 nm.