### Session PA: Optics

Chair: Brian Thoms, Georgia State University
Room: Brussels

 Saturday, November 14, 2009 10:45AM - 10:57AM PA.00001: Single-grating and single-grism pulse compressors. Vikrant Chauhan , Pamela Bowlan , Jacob Cohen , Rick Trebino We introduce single-diffraction element pulse compressors, which use a single grating or a grism, and are compact and automatically aligned for distortion-free output. A pulse compressor adds negative GDD by introducing angular dispersion, which yields negative GDD but also introduces other spatio-temporal distortions, like spatial chirp and pulse-front tilt, which must be removed before using the pulse. They have four (or two) identical dispersive elements, arranged, not only to introduce negative GDD, but also to then compensate for the spatio-temporal distortions. So, traditional designs are bulky and difficult to align for zero spatio temporal distortions. We recently solved these problems in our single-prism pulse compressor. But prism compressors have limited negative GDD. Using gratings increases the GDD but gratings have a negative ratio of third-order dispersion (TOD) to GDD, materials introduce a positive ratio, so, they cannot compensate for both simultaneously. A single grism pulse compressor solves this problem and adds large amounts of negative GDD. In addition, it is compact, is auto-aligned for distortion-free output, and has a tunable TOD-to-GDD ratio, so it can compensate for a wide range of materials. Saturday, November 14, 2009 10:57AM - 11:09AM PA.00002: Non Specular Diffractive Optics Yunjin Wang , Dan Overcash , Pawel Morawice , Ming Yin , Timir Datta Geometrically decorated two-dimensional (2D) discrete surfaces can be more effective than conventional smooth reflectors in managing wave radiation. Constructive non-specular wave scattering permits the scattering angle to be other than twice that of incidence and can result in gross violations of the law of reflection. A wide range of novel reflective behaviors ensues; including the phenomenon of negative reflection were energy transport remains on the same side of the normal. Also, at a critical incidence coherent superposition can force both the transmitted and reflected waves to graze the scattering surface thus synergistically reinforcing the diffractive process in a behavior reminiscent of critical internal reflection of ray optics. We experimentally demonstrate the concept with measurements on a one-dimensionally periodic system (grating) where the scattering angle is shown to be an inverse circular function of a function that depends on the diffractive index and the two angles. Excellent agreement is found between experimental data and theory. A preliminary report on our observations will be discussed. Saturday, November 14, 2009 11:09AM - 11:21AM PA.00003: Infrared -- Submillimeter Wave Double Resonance Experiments and Extension of Technique to Atmospheric Pressure Spectroscopy Dane J. Phillips , Henry O. Everitt , Frank C. De Lucia Double resonance spectroscopy involves the excitation of a system into a state of non-thermal equilibrium population distribution and the subsequent probing of that non thermal equilibrium for the analysis of energy pathways of the molecule interactions. In infrared -- submillimeter (IR/SMM-THz) double resonance this involves the excitation of rotational-vibrational levels of a molecule producing a non-thermal rotational energy level distribution in an excited vibrational state. The extension of this double resonance technique into the higher pressures involves understanding the collisional physics in a new pressure regime and the subsequent, collision partner dependent, interactions of these collisions with various energy manifolds. The spectroscopic signature provided by probing the excited systems rotational energy distribution provides a greatly enhance specificity to that achieved with analysis traditional SMM/THz spectroscopy. Preliminary experimental results on time resolved collisional data of atmospheric constituent gases with prototypical analyte molecules will be presented in the context of double resonance techniques in atmospheric pressures. Saturday, November 14, 2009 11:21AM - 11:33AM PA.00004: ABSTRACT WITHDRAWN Saturday, November 14, 2009 11:33AM - 11:45AM PA.00005: Stored Light under conditions of electromagnetically induced transparency and four-wave mixing in an optically dense atomic gas Nathaniel Phillips , Alexey Gorshkov , Irina Novikova A promising avenue towards efficient and reliable quantum communication is based on light storage via electromagnetically induced transparency (EIT) in an optically thick atomic gas. A strong classical control field modifies the optical properties of a weak signal field such that a previously opaque medium becomes transparent to the signal field. The accompanying steep dispersion in refractive index enables pulses of light to be decelerated, then stored as an atomic excitation, and later retrieved as a photonic mode. In any storage device, the objective is to minimize losses during storage time and maximize the read efficiency. With consideration to an atomic gas, these criteria are met when the gas density, and hence optical depth, is high. However, at high optical depth, resonant four-wave mixing (FWM), in which a near-resonant Stokes field is simultaneously created by the interaction of probe and control photons, interferes with EIT and disturbs the memory. We experimentally and theoretically study stored light in a hot $^{87}$Rb gas under conditions of EIT and FWM, and show that a seeded Stokes pulse largely affects the FWM-EIT interaction. We further discuss the prospect of simultaneously storing signal and Stokes pulses and investigate the memory decay in both channels. Saturday, November 14, 2009 11:45AM - 11:57AM PA.00006: Numerical investigation of two-beam coupling in hybrid liquid crystal-photorefractive cells using the finite-difference time-domain method Thomas E. Lanier , William M. Dennis , Gary Cook , Dean R. Evans , Victor Reshetnyak Photorefractive two-beam coupling is a nonlinear optical phenomenon that finds application in a range of photonic devices. The spatially modulated refractive index due to the space-charge field that arises from the interference pattern generated by crossed laser beams is responsible for two-beam coupling in photorefractive materials. Penetration of this field into the region surrounding the photorefractive results in the reorientation of liquid crystal molecules, providing a mechanism for enhancement of two-beam coupling. We present a numerical investigation of two-beam coupling in organic-inorganic hybrid cells consisting of a liquid crystal layer sandwiched between two photorefractive windows. Finite-difference time-domain calculations of beam propagation in such hybrid cells are carried out using the electric permittivity tensor field derived from the liquid crystal director spatial profile in steady state. Saturday, November 14, 2009 11:57AM - 12:09PM PA.00007: Simply Measuring the Electric Field of Very Long, Complex Pulses Jacob Cohen , Pamela Bowlan , Rick Trebino We introduce a method for measuring both the intensity and the phase of arbitrary ultrafast waveforms in time ($\sim$1 ns long, with $<$100-fs substructure). It is an extension of a simple version of spectral interferometry called SEA TADPOLE, and we call it MUltiple Delay for Temporal Analysis by Dispersing a Pair of Light E-fields (MUD TADPOLE). In contrast to standard versions of spectral interferometry, MUD TADPOLE utilizes, not one, but a train of identical parallel-propagating reference pulses. These multiple reference pulses are used because each pulse broadens in time inside the spectrometer by the reciprocal of the spectrometer spectral resolution, $t_{sp}$. In the case of standard spectral interferometry, one reference pulse can, at best, measure light only $t_{sp}$ long. In contrast, by utilizing a train of $N$ reference pulses, MUD TADOPLE has the capability to measure light which is $N*t_{sp}$ long. MUD TADPOLE has been demonstrated to measure complex pulses up to 71ps in length. We believe this simple, compact, and inexpensive device can measure pulses with time-bandwidth products in excess of 100,000 using off-the-shelf components. Saturday, November 14, 2009 12:09PM - 12:21PM PA.00008: Nonlinear optical absorption in the blue spectral region by phosphine-substituted oligothiophenes Jianwei Wang , Christopher Lawson , Qun Zhao , Gary Gray Organic conjugated materials with large nonlinear optical (NLO) absorption have potential applications in optical computing, optical switching and optical power limiting. However, nearly all investigations have focused on the green, red and near-infrared regions of the optical spectrum. In contrast, organic conjugated materials exhibiting NLO absorption in the blue region have not been reported. Phosphine-substituted oligothiophenes are among the few materials that exhibit nonlinear optical absorption in the blue spectral region. Three families of these materials have been investigated, and the best blue absorber at 430 nm is 5,5'-bis(diphenylphosphine selenide)-2,2'-bithiophene. Saturday, November 14, 2009 12:21PM - 12:33PM PA.00009: Ultraviolet-Infrared dual band detector using ZnO/PbS composite nanostructure P.K.D.D.P. Pitigala , P.V.V. Jayaweera , J. Shao , K. Tennakone , A.G.U. Perera , P.M. Jayaweera , J. Baltrusaitis Sensors for detecting ultraviolet (UV) and near-infrared (NIR) photons, fabricated by complex epitaxial methods are costly. A low cost UV-NIR detector is fabricated using ZnO nonporous powder and PbS quantum size particles is demonstrated. A nonporous film of ZnO was fabricated on Fluorine doped Tin Oxide (FTO) glass with a scribe, separating the FTO layer in to two electrodes. PbS quantum particles were composites on the ZnO film by wetting the film using a solution of lead acetate in ethanol and passing a stream of H$_{2}$S gas on top of the film. When a bias voltage is applied across the electrodes the device shows two response peaks, around 380nm (UV) and 800nm (NIR). These two responses are resulted due to bandgap excitation of ZnO ($\sim$3.2 eV) and PbS ($\sim$0.9 eV) quantum particles.