Vladimir I. Emel'yanov

A PHOTONIC SWITCH BASED ON A GIGANTIC, REVERSIBLE OPTICAL NONLINEARITY OF LIQUEFYING GALLIUM

Liquefying gallium shows a huge reversible optical nonlinearity which is compatible with waveguide technology and promises to be a breakthrough in broadband, light-by-light modulation at milliwatt operating power levels and frequency band spanning up to several hundred kilohertz.

Light-induced metallization in laser-deposited gallium films

We have found that mirrors prepared upon silica glass by ultrafast pulsed laser deposition of elemental gallium show a highly reproducible and fully reversible light-induced reflectivity increase. The effect is explained as being due to nonthermal light-induced metallization of gallium at the interface.

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 The reflectivity relaxes back to that of a-gallium when the excitation is withdrawn in a time that increases critically at gallium’s melting point.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

Controlling the coexistence of structural phases and the optical properties of gallium nanoparticles with optical excitation

We have observed reversible structural transformations, induced by optical excitation at 1.55 μm, between the β, γ and liquid phases of gallium in self-assembled gallium nanoparticles, with a narrow size distribution around 50 nm, on the tip of an optical fiber. Only a few tens of nanowatts of optical excitation per particle are required to control the transformations, which take the form of a dynamic phase coexistence and are accompanied by substantial changes in the optical properties of the nanoparticle film. The time needed to achieve phase equilibrium is in the microsecond range, and increases sharply near the transition temperatures.

Femtosecond dynamics of laser-induced phase transition of the GaAs surface layer to a centrosymmetric phase

Abstract Recently we observed ultrafast laser-induced phase transition (on a time scale less than 100 fs) to a centrosymmetric semiconductor-like phase at the GaAs surface [1,2] by using time-resolved second harmonic generation in reflection. A phenomenological model describing this phase transition is developed. The new phase exists during the first 1 ps after laser excitation due to high plasma carrier density and lattice stress, the lattice temperature remaining well below the melting threshold.

Transition from quasi-hexagonal to quasi-one dimensional pores distribution during deep anodic etching of uniaxial stressed silicon plate

A gradual transition from quasi-hexagonal to quasi-one dimensional pore distribution during deep anodic etching of a uniaxially stressed silicon plate was experimentally observed to increase with mechanical loading.

Theory of single-pulse laser amorphization of semiconductors

The theory of amorphization under pulsed laser melting of surfaces of crystalline semiconductors, based on mechanism of point defect capture and formation of nanometer periodic defect-deformational structures, is developed. The critical defect concentration and critical solidification front velocity at exceeding of which amorphization occurs are determined. The hierarchy of structural transformations at surface after melt solidification observed with decrease of laser fluency is analytically described.

Nonlinear multimode dynamics of the formation of deformation defect mesostructures in crystals under radiation

Two-stage dynamics of the self-organization of three-dimensional cluster-and periodic deformation defect mesostructures in cubic crystals under radiation is considered and the criteria of mesostructure self-organization are formulated.

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.

First observation of light-controlled self-assembly of gallium nanoparticles with narrow size dispersion

Summary form only given. We report growth processes that control the shape and size of particles as they form, through non-thermal processes, using a low-power (/spl sim/ few mW) infrared diode laser. We study nanoparticle formation on the ends of optical fibers exposed to a gallium atomic-beam source under high vacuum. The results of the experiments and numerical modeling indicate that the growth of gallium nanoparticles in a laser-illuminated area is controlled through non-thermal laser-induced processes. We expect that by changing the deposition conditions (atomic beam flux, substrate temperature, etc.) and laser parameters (wavelength, power, etc.), the size, shape and spatial distribution of nanoparticles could be varied.