Bragg Reflection of Light from Single-Domain Cholesteric Liquid-Crystal Films

Abstract

Theoretical estimates of the neutron production in the Columbia University shock tube, for a shock speed of 100 cm/Msec, predicted about 4x 10 5 neutrons. Four 1B85 thyrode Geiger tubes, wrapped in 10-mil silver sheet and covered with a polyethylene moderator, were placed about the 50-cm point on the shock tube. For slightly slower shock speeds than shown in Table I no neutrons were observed. However, for the shock speeds indicated in Table I, neutrons have been detected, and by using a Los Alamos calibration 7 for this detector, we estimate a yield of about 5xl0 5 neutrons. However, the close agreement between predictions and this measurement is thought to be more fortuitous than an indication of accuracy. A pilot B scintillator, shielded by 1 in. of lead, detected a burst of radiation which may be neutrons or nonthermal hard x rays. We do not know yet whether the neutrons are truly of thermonuclear origin.The experimental data indicate that the shockcreated plasma volume of ~10 4 cm 3 has an internal energy density (nkT) of about 1.2 J/cm 3 , a macroscopic kinetic energy (IpF 2 ) of about 2.8 J/cm 3 , and that about 20% of the energy originally stored in the high-voltage capacitor bank was transferred into the plasma in the first halfcycle of the current pulse.We acknowledge the many contributions by Dr. B. Miller in the design and early develop-Almost all previous optical studies of cholesteric liquid-crystal films were made on systems composed of cholesterol-derived molecules. The optical properties of these films were qualitatively explained by assuming a distribution in orientation of Bragg scattering domains embedded in a matrix of constant refractive index. 1 Adams and co-workers have shown that, among other difficulties, inhomogeneity in Bragg spacing makes it impractical to measure this angular ment of the shock tube, and thank Mr. M. Cea,

Polymer concentration profile near a liquid-solid interface: evanescent wave ellipsometry study

“…3 • 4 Little is understood about these sugar acid polymers' higher order structure 5 or how they form ordered arrays with a minimization of interaction energy in the native state. 6 The associations of various polysaccharides in gels have been investigated, 7 and different types of interaction profiles between macromolecules can be distinguished. A gel structure has been proposed to exist through the exclusion of incompatible coils and the realignment of stiff structures with more compatible geometries to form mixed aggregates.…”

“…A quantitative calculation of the phase difference as a function of the incident angle can be done with the Jones wave propagational matrix, 7 assuming a specific polymer concentration profile. The dielectric content e(z) is related with the polymer concentration profile <P(z), such as…”

Spin Controlled Optical Radiation Pressure

“…A helical arrangement of the optical axis indeed combines dielectric periodic structuration, which leads to a Bragg photonic band gap, with chirality, which brings circular polarization sensitivity. A famous example is the circular Bragg reflection phenomenon in cholesteric liquid crystals [5], which we use here to experimentally demonstrate how mechanical effects driven by the radiation pressure of light can be fully controlled by the spin of photons. The principle of our experiment is sketched in Fig.…”

Optofluidic sorting of material chirality by chiral light

“…More precisely, the black circular area of radius R B for the chiral droplet shown in Fig. 2e corresponds to the circular Bragg reflection phenomenon, which is a generic optical property of cholesteric liquid crystals 24 . It refers to the fact that the propagation of light in one of the two circular polarization states along the cholesteric helical axis is forbidden over a well-defined wavelength range Dl ¼ p(n 8 À n > ) centred on the Bragg wavelength l B ¼ np where n ¼ (n 8 À n > )/2 is the average refractive index of the cholesteric with n 8,> the refractive indices parallel and perpendicular to n. By deliberately choosing Bragg cholesteric droplets, enhanced optomechanical separation of droplets having opposite chirality is achieved at relatively low optical power due to helicity-dependent optical radiation pressure exerted on the droplets 25 .…”