Search results for "Refractive"

Refractive index sensor based on whispering gallery modes resonances of thin capillaries

2007

Strong lowering of the mirrorless optical oscillation threshold by angular mismatches for nonlocal photorefractive nonlinearity.

2008

We show that the introduction of an angular mismatch for the pump waves results, in the case of nonlocal photorefractive nonlinearity, in a strong almost twofold decrease of the threshold value of the coupling strength for the mirrorless optical oscillation. This surprising feature will lead to a strong modification of the threshold and near-threshold behavior of a vast variety of optical oscillators based on the photorefractive phase conjugation and involving finite-size light beams.

Nonlinear dynamics of a semilinear photorefractive oscillator

2001

The experimental study of the dynamics of an empty coherent semilinear photorefractive oscillator is reported. It is shown that starting from a certain coupling strength the oscillation occurs with two frequencies shifted symmetrically with respect to the frequency of the pump wave. The threshold of bifurcation in oscillation spectrum depends on pump intensity ratio.

Interaction between non-Bragg band gaps in 1D metamaterial photonic crystals

2009

We consider periodic multilayers combining ordinary positive index materials and dispersive metamaterials with negative index in some frequency range. These structures can exhibit photonic band gaps which, in contrast with the usual Bragg gaps, are not based on interference mechanisms. We focus on effects produced by the interaction between non-Bragg gaps of different nature: a) the zero averaged refractive index, b) the zero permeability and c) the zero permittivity gaps. Our analysis highlights the role played by the unavoidable dispersive character of metamaterials. We show that the degree of overlap between these bands can be varied by a proper selection of the constructive parameters, …

Oscillation spectra of semilinear photorefractive coherent oscillator with two pump waves

2002

The transition of the single-frequency oscillation of a semilinear photorefractive coherent oscillator for sufficiently large coupling strengths into two-frequency oscillation is predicted and is observed experimentally. The critical value of coupling strength at which the bifurcation occurs is a function of pump-intensity ratio and cavity losses. For certain combinations of these parameters, the critical coupling strength for spectrum bifurcation becomes smaller than the threshold coupling strength: in these cases double-frequency oscillation appears at the threshold. The supercritical bifurcation in the oscillation spectrum is analogous to the second-order phase transition.

Instability of single-frequency operation in semilinear photorefractive coherent oscillators.

2002

The transition of the single-frequency oscillation of a semilinear photorefractive coherent oscillator for sufficiently large coupling strengths into two-frequency oscillation is predicted and is observed experimentally. The critical value of the coupling strength at which the bifurcation occurs is a function of pump intensity ratio and cavity losses. The supercritical bifurcation in the oscillation spectrum is analogous to the second-order phase transition.

Second-order optical phase transition in a semilinear photorefractive oscillator with two counterpropagating pump waves

2002

Soft-mode onset of coherent oscillation is revealed in a semilinear cavity with two counterpropagating pump waves. From the dynamics of the oscillation intensity and the dynamics of the grating decay with the feedback applied, critical behavior is detected: Both the characteristic time of oscillation onset and grating decay time go to infinity exactly at the threshold coupling strength. A conclusion is made about the similarity of this type of oscillator to the second-order phase transition.

Acousto-optical multiple interference switches

2007

The authors introduce an alternative approach for acousto-optical light control based on the interference of light propagating through several waveguides, each subjected to a periodic refractive index modulation induced by a surface acoustic wave. The feasibility of the concept is demonstrated by the realization of an optical switch for arbitrary time intervals with an on/off contrast ratio of 20.

The Elliptical Polarization of Light Scattered by a Volume of Atmospheric Air

2010

The scattering of linearly polarized light by aerosol particles produces partly polarized light whose ellipticity is theoretically and experimentally investigated for the specific case of a continental atmospheric aerosol in a volume of air. With the Mie theory and under the assumption of various aerosol size-distribution models, the ellipticity has been computed as a function of the scattering angle for various wavelengths. The computations have been based upon complex indices of refraction: M = 1.5-0.0i, M = 1.5-0.0li, M = 1.5-0.li, M = 1.44-0.0i, M = 1.4-0.0i, M = 1.33-0.0i. The comparison between computed and measured values for the wavelengths of lambda = 0.45 micro to lambda = 0.65 mi…

Slowdown and speedup of light pulses using the self-compensating photorefractive response

2011

We study theoretically the effects of pulse slowdown and speedup in ferroelectric Sn2P2S6 possessing a self-compensating photorefractive response. It is shown that both these effects can be implemented in one sample for sufficiently large values of the coupling strength. In contrast to other types of the photorefractive response (local and nonlocal), the output pulses do not suffer from strong spatial amplification and broadening.