S. Dhanjal

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.

Passive Q-switching of fiber lasers using a broadband liquefying gallium mirror

Using a nonlinear cavity element, a liquefying gallium mirror, we demonstrate stable, self-starting, passive Q-switching of both erbium and ytterbium fiber laser cavities operating at wavelengths of 1550 and 1030 nm, respectively. The performance at 1550 nm is shown to be equivalent to that achieved with a state of the art semiconductor saturable absorber designed to work at this wavelength. The results highlight the suitability of this tremendously broadband, inexpensive nonlinear medium for a wide range of passive Q-switch applications.

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 The reflectivity relaxes back to that of a-gallium when the excitation is withdrawn in a time that increases critically at gallium’s melting point.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 optical nonlinearity of metallic indium across the solid–liquid transition

A very strong (~10(-8) esu) femtosecond cubic nonlinearity in metallic indium that increased sharply in magnitude as the temperature approached the melting point was observed.

Passive Q-switching of an Er3+:Yb3+ fibre laser with a fibrised liquefying gallium mirror

Abstract We report a new technique for passive Q-switching of low-power lasers, which exploits nonlinear reflection from a liquefying gallium mirror. Self-start Q-switching has been achieved in an Er 3+ :Yb 3+ fibre laser for circulating intracavity powers of only a few milliwatts. The laser produced a continuous train of pulses as short as 1 μs at repetition rates of a few tens of kilohertz and with peak powers of 0.5 W. Due to the broadband reflective nature of the nonlinearity of gallium, the technique should be applicable to a wide range of laser systems.

Optical detection of crystallographic domains in zinc-blende crystals

We introduce an experimental technique which allows the characterization of domains in nonmagnetic cubic crystals of the zinc-blende type. The technique exploits the optical anisotropy of cubic crystals near an excitonic resonance which translates to a dependence of the reflected light polarization on crystal orientation. We demonstrate sub 10 μm domains on the [110] surface of a high quality, homoepitaxially grown ZnSe film.

Nonreciprocity of natural rotatory power

We have observed that a light beam that passed through an optically active crystal of Bi(12)SiO(20) and that was then ref lected exactly back through it did not recover its initial polarization orientation. The nonreciprocal component of the rotation was of the order of 2 x 10(-3) of the reciprocal, single-pass rotation. This nonreciprocity is unambiguous evidence of broken reversality of the light-matter interaction process.

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.

Cubic optical nonlinearities of metals in the vicinity of the melting point

Abstract We report the first study of frequency degenerate cubic optical nonlinearities in bulk metals across the melting point. Using pump–probe reflectivity and precise pump–probe polarimetry a strong femtosecond electronic nonlinearity (X (3) ≈ 10−8 esu) has been observed in indium. The effective nonlinearity sharply increases when the temperature approaches the melting point. We also report the results of a study on the nonlinearity of nickel films and discuss the effect of an interface with glass on the magnitude and sign of the nonlinearity.