ABSTRACT
Cholesteric liquid crystals (CLCs) with induced defects are one of the most prominent materials to realize compact, low-threshold and tunable coherent light sources. In this context, the investigation of optical properties of induced defect modes in such CLCs is of great interest. In particular, many studies have been devoted to the spectral control of the defect modes depending on their thickness, optical properties, distribution along the CLC, etc. In this paper, we investigate the lasing possibilities of a dye-doped polymer layer embedded in a wedge-shaped CLC. We show that multimode laser generation is possible due to the observed multiple defect modes in the PBG that enlarges the application range of the system. Furthermore, our simulations based on a Berreman 4 × 4 matrix approach for a wide range of CLC thickness show both periodic and continuous generation of defect modes along particular spectral lines inside the PBG. Such a robust spectral behaviour of induced defect modes is unique, and, to our knowledge, is not observed in similar CLC-based structures.
ABSTRACT
In our paper, the magneto-optical properties of a dichroic cholesteric liquid crystal layer with large values of magneto-optical parameter g and low values of dielectric permittivity were investigated. The solutions of the dispersion equation and their peculiarities were investigated in detail. The specific properties of reflection, transmission, absorption, rotation, ellipticity spectra and also the spectra of ellipticity and azimuth of eigen polarization were investigated. The existence of a tunable linear and nonreciprocal transmission band was shown.
ABSTRACT
We report on the experiments on the interaction of gigawatt femtosecond laser pulses with suspended millimeter-sized water droplets. The transparent droplets experienced laser-induced breakdown and explosive boiling up and emitted a broadband radiation. This radiation covers the spectral range from 450 to 1100 nm and consists of the spectrum of laser pulse scattered and transformed by the droplet due to self-phase modulation and plasma emission produced in water during photoionization. The droplet emission spectrum showed remarkable broadening at all viewing angles and is maximal in the direction of the laser exit from the droplet. The enlargement of the droplet results in additional spectral spreading of the emitted radiation. The depth and amount of laser pulse spectral self-transformations upon propagation through the water droplet are simulated by means of numerical calculations.
ABSTRACT
We report on experiments on the interaction of a gigawatt femtosecond laser pulse train with hanging isolated millimeter-sized water droplets. A transparent droplet experienced explosive boiling-up and emitted light in the visible spectrum as a result of laser-induced plasma formed inside the droplet volume. The droplet emission spectra showed remarkable broadening, depending on the laser power. The role of pulse self-phase modulation in measured spectral broadening when the pulse propagates through the droplet is discussed.
