Spectral singularities and threshold gain of a slab laser under illumination of a focused Gaussian beam

We study spectral singularities of an infinite planar slab of homogeneous optically active material in focus of a thin lens under illumination of a Gaussian beam. We describe the field distribution of the Gaussian beam under this configuration as a plane wave propagated near the optical axis which its phase and amplitude vary with distance from center of the beam. Based on this approximation, we carry out the transfer matrix for the slab. We explore the consequences of this configuration on determining the threshold gain of the active medium and tuning the resonance frequencies related to spectral singularities. We show that the spectral singularities and the threshold gain besides that vary with distance from center of the Gaussian beam, also they change with relative aperture of the focusing lens. As a result, using a thin lens with higher relative aperture, the spectral singularities corresponding resonances shift to the higher frequencies (lower wavelengths). Numerical results confirm the theoretical findingsComment: 11 pages, 6 figure

Topologically driven Rabi-oscillating interference dislocation

Quantum vortices are the quantized version of classical vortices. Their center is a phase singularity or vortex core around which the flow of particles as a whole circulates and is typical in superfluids, condensates and optical fields. However, the exploration of the motion of the phase singularities in coherently-coupled systems is still underway. We theoretically analyze the propagation of an interference dislocation in the regime of strong coupling between light and matter, with strong mass imbalance, corresponding to the case of microcavity exciton-polaritons. To this end, we utilize combinations of vortex and tightly focused Gaussian beams, which are introduced through resonant pulsed pumping. We show that a dislocation originates from self-interference fringes, due to the non-parabolic dispersion of polaritons combined with moving Rabi-oscillating vortices. The morphology of singularities is analyzed in the Poincar\'{e} space for the pseudospin associated to the polariton states. The resulting beam carries orbital angular momentum with decaying oscillations due to the loss of overlap between the normal modes of the polariton system.Comment: 9 pages, 6 figure

Bleaching and Darkening Effect in Photochromic Glasses under Irradiation with Femtosecond Laser Pulses

In this paper, the photochromic oxide glass sample under interaction of 200 fs laser pulses at 800 nm wavelength is studied. Two types of laser-induced modifications, bleaching and darkening, are observed. The induced darkening is observed inside the bleached volume. The effect of incident laser shot number and pulse energy on the bleached and darkened area are investigated. The pulse energy accumulation model is applied to investigation of both bleached and darkened area sizes. The bleaching and darkening modification fluence threshold are determined for single and multi-shot laser pulses

Nonlinear Responses and Optical Properties Modification οf SK3 under Irradiation of Femtosecond Laser Pulses

In this paper, the nonlinear responses and optical properties modification in SK3 glass sample are investigated. The nonlinear responses measurements were performed by using of nonlinear transmission monitoring of 200 fs at 800 nm laser pulses. The optical power limiting threshold of the sample is measured to be about 40 mJ/$cm^{2}$. The decrease of transmitted intensity is about 63% compared to the theoretical linear transmission at 270 mJ/$cm^{2}$ incident pulse energy. For prediction of the experimental nonlinear behavior results, a theoretical model based on three-photon absorption and absorption of free carriers is presented. By fitting of experimental data with theoretical model, three-photon absorption coefficient and free-carrier absorption cross-section are reported. The photo-induced optical properties modification of the SK3 sample is investigated also. The modifications that appear as darkening are observed below breakdown threshold intensity. To analyses of modified region sizes, the laser pulse energy accumulation model is applied

One-way absorption behaviour in defective 1D dielectric-metal photonic crystal

In this paper, the one-way absorption property in one-dimensional dielectric/metal photonic crystal structure with a dielectric defect layer is studied. The effects of incident angle and state of polarization on one-way absorption behaviour of the anti-resonant (AR) mode are investigated. The normally incident wave from left to right propagation is totally allowed to penetrate to the structure but right to left propagation totally reflected at the same wavelength. It is found that, with increasing of the incident angle, the AR mode shifts to the lower wavelengths and its intensity decreases. Simultaneously, another AR mode with reversed one-way property appears at higher wavelength. The one-way behaviour on absorption is observed at the both states of polarizations but is localized on different wavelengths. Those effects, are suggesting that the proposed structure can be used as a direction sense polarization splitter or reflector/antireflector device

IR femtosecond laser microstructuring of photochromic glasses

The interaction of the near IR femtosecond laser pulses with photochromic glass sample is investigated. Two different types of microstructures due to the optical properties modification of the sample are observed at the irradiated regions with single laser pulses. Laser fluence and shot number dependency of the structures are investigated. The optical transmission of irradiated areas is analyzed spectroscopically

Effect of Linear Absorption on Efficiency of SHG in Layered Structure

The effect of linear absorptions on conversion efficiency of the fundamental radiation to the second harmonic wave in a layered structure is investigated under intensity constant approximation. Behaviour of the conversion efficiency after each layer, up to third layer, is graphically illustrated