Beam combining using Orientational Stimulated Scattering in Liquid Crystals

Possibility of beam combining and clean-up using Orientational Stimulated Scattering in a Nematic Liquid Crystal is considered. We numerically study the dynamics of the process and find that back-conversion process tends to limit the effective interaction strength. Instability of the steady state of cross-phase modulation is demonstrated, when both waves have the same frequency. We show that high conversion efficiency can be achieved, and that the shape and wave-front of the amplified output signal are robust with respect to amplitude and phase distortions of the input pump.Comment: 24 pages, 6 figures, will be published in JOSA

Periodically Aligned Liquid Crystal: Potential application for projection displays

A nematic liquid crystal (NLC) layer with the anisotropy axis modulated at a fixed rate q in the transverse direction is considered. If the layer locally constitutes a half-wave plate, then the thin-screen approximation predicts 100% -efficient diffraction of normal incident wave. The possibility of implementing such a layer via anchoring at both surfaces of a cell with thickness L is studied as a function of parameter qL and threshold values of this parameter are found for a variety of cases. Distortions of the structure of director in comparison with the preferable ideal profile are found via numerical modeling. Freedericksz transition is studied for this configuration. Coupled-mode theory is applied to light propagation through such cell allowing to account for walk-off effects and effects of nematic distortion. In summary, this cell is suggested as a means for projection display; high efficiency is predicted.Comment: 25 pages, 6 figures, 1 tabl

Multi-Wavelength Infared Laser

A long wavelength infrared laser system is disclosed where radiation from laser sources such as frequency-doubled Nd:YAG or a Cr:LiSAF is used to resonantly pump a gain medium consisting of a holmium-doped fluoride crystal having a high active ion concentration. The laser pump source has a pulse duration that may be short enough to gain switch a particular transition or long enough to allow end-pumping with high energy densities without damage. The gain material has an absorption approximately resonant with the pump source wavelength, and the dopant concentration is selected to maximize absorption strength for a given excitation. The output radiation from the laser system consists of one or more wavelengths including, in particular 3.9 nm but also other infrared wavelgths such as 1.4 .mu.m, 2.9 .mu.m and 3.4 .mu.m., several of which may be produced simultaneousely from the same laser material through the mechanism of cascade transitions

Thermomechanical effects in uniformly aligned dye-doped nematic liquid crystals

We show theoretically that thermomechanical effects in dye-doped nematic liquid crystals when illuminated by laser beams, can become important and lead to molecular reorientation at intensities substantially lower than that needed for optical Fr\'eedericksz transition. We propose a 1D model that assumes homogenous intensity distribution in the plane of the layer and is capable to describe such a thermally induced threshold lowering. We consider a particular geometry, with a linearly polarized light incident perpendicularly on a layer of homeotropically aligned dye-doped nematics

Electro-optical characteristics of a liquid crystal cell with graphene electrodes.

In liquid crystal devices (LCDs) the indium tin oxide (ITO) films are traditionally used as transparent and conductive electrodes. However, today, due to the development of multichannel optical communication, the need for flexible LCDs and multilayer structures has grown. For this application ITO films cannot be used in principle. For this problem, graphene (an ultrathin material with unique properties, e.g., high optical transparency, chemical inertness, excellent conductivity) is an excellent candidate. In this work, the electro-optical and dynamic characteristics of a liquid crystal (LC) cell with graphene and ITO transparent conducting layers are investigated. To insure uniform thickness of the LC layer, as well as the same orientation boundary conditions, a hybrid LC cell containing graphene and ITO conductive layers has been prepared. The characteristics of LC cells with both types of conducting layers were found to be similar, indicating that graphene can be successfully used as a transparent conductive layer in LC devices

Route to nonlocality and observation of accessible solitons

We develop a general theory of spatial solitons in a liquid crystalline medium exhibiting a nonlinearity with an arbitrary degree of effective nonlocality. The model accounts the observability of "accessible solitons" and establishes an important link with parametric solitons.Comment: 4 pages, 2 figure

Incoherent interaction of nematicons in bias-free liquid-crystal cells

We study experimentally the propagation dynamics and interaction of a pair of mutually incoherent nematicons: spatial optical solitons in nematic liquid crystals. In contrast to earlier studies, we consider a bias-free liquid-crystal cell and compare the soliton interaction in copropagating and counterpropagating geometries. We analyze the dependence of nematicon interaction on input power and observe a direct manifestation of a long-range nonlocal nonlinearity. Attraction of counterpropagating solitons requires higher powers and longer relaxation times than that of copropagating nematicons due to losses-induced power asymmetry of counterpropagating nematicons.Comment: 5 pages, z figure

Exploring the High Redshift Universe: Spectral Analysis Methods along Quasar Sight Lines

Luminous quasars (QSOs) serve as powerful beacons for probing the intergalactic medium (IGM). Lyman-alpha (Lyα) forests – absorption lines attributed to the presence of neutral hydrogen in the IGM – are regularly observed in QSO spectra. Lyα lines provide critical cosmological information regarding both, the distribution of gas clouds in the IGM at different redshifts, and the Epoch of Reionization (EoR) following the formation of the universe’s first luminous energy sources. IGM opacity (and thus the fraction of hydrogen that is neutral) is estimated as a function of redshift by measuring how much of the intrinsic emission of QSOs are absorbed along each of their sight lines. This measurement requires estimation of the intrinsic emission of each QSO, which is found by fitting their continua. For very high redshift QSOs, there is so much absorption along their sight lines, only the continuum redward of each QSO’s Lyα peak can be fitted. This thesis proposes a method for a first-look estimation of relative neutral hydrogen absorption in the absence of a complex continuum fitting model. Capitalizing on public datasets from Sloan Digital Sky Survey (SDSS) and QSO spectra database igmspec, high redshift QSO spectra are fit with Gaussians where Lyα absorption is estimated by subtracting the fitted flux levels at wavelengths directly preceding the Lyα emission line with the unabsorbed flux levels after. The proposed method provides a rapid method for a statistical assessment of IGM opacity during the EoR complementary to more sophisticated PCA-based continuum fitting models. Looking forward, the spectroscopic advances of the James Webb Space Telescope (JWST) and the telescope’s potential to address tensions between novel, extremely-high redshift QSO discoveries and Big Bang cosmology are discussed

Beam Clean-Up And Combining Using Orientational Stimulated Scattering In Liquid Crystals

Beam clean-up and combining using Stimulated Orientational Scattering in nematics is considered. Dynamics of the process is studied, high conversion efficiency and stability with respect to pump fluctuations is demonstrated. © 2005 Optical Society of America