Light-induced structural phase transition in confining gallium and associated gigantic optical nonlinearity

Albanis, V., Dhanjal, S., Petropoulos, P., Richardson, D.J., Zheludev, N. and Emelyanov, V. (1998) Light-induced structural phase transition in confining gallium and associated gigantic optical nonlinearity. MRS Fall Meeting, Boston, United States. 30 Nov - 04 Dec 1998.

Abstract

We discovered a new type of light-induced structural surface assisted phase transition, which occurs in the vicinity, but below the bulk melting point (29.6C) of metallic alpha-gallium interfacing with a dielectric such as silica or glass. The transition is not a thermal effect, but is provoked by an optical destabilisation of the covalent bonding structure of alpha-gallium. The transition is to a more reflective, metastable 'metallic' like phase. The light penetrates only about 25 nm in gallium, with only several tens of atomic layers of the metal being affected by the phase transition. This is enough to change the interface reflectivity significantly, on several tens of percent. The light-induced phase has not been precisely identified yet, but several metastable phases of crystalline gallium and quasi liquid state are potential candidates. The phase transition may be stimulated with light of a very low intensity and wavelength spanning from 0.5 to 1.6µm. The thickness of the metallized layer and its reflectivity increase with the light intensity and the phase transition is fully reversible if the light is withdrawn. The transitions between the phases occur very fast, on nanosecond - microsecond time scales, depending on the sample temperature. The recovery time of the alpha-phase critically increases when the interface temperature approaches the material's melting point, as it would be appropriate for a second order phase transition. We also observed a self-oscillatory reaction on optical excitation of confining gallium layers of only a few nanometres thick. As the intensity of light necessary to stimulate the phase transition is very low, and only a few milliwatts of laser lower is required to observe it, the discovered metallic-dielectric structure has immense potential for waveguide photonic applications and optical data processing and storage.

This record has no associated files available for download.

Contributors

Author: P. Petropoulos

Author: D.J. Richardson

Author: N. Zheludev

Download statistics