Liquid crystals possess many novel electro- and nonlinear optical properties and physical characteristics such as extraordinarily large and tunable birefringence over the entire visible-infrared regime and compatibility with almost all optoelectronic materials. Their fluid like nature allow easy incorporation of nano-particulates or infiltration into nano-structures such as photonic crystals, channel waveguides, as well as plasmonic nano-structures [1]. As a result of the extreme sensitivity of the plasmonic resonances and dispersion to changes in the surrounding dielectric constant, the combined systems exhibit new tunable (by electric or optical fields) resonances. In this presentation, we will present a critical review of these studies and our recent work on liquid-crystals-plasmonic materials and nano-structures that combine the unique physical and optical properties of both materials to enable a new generation of reflective, transmissive, modulation and switching elements and devices. In particular, we will elaborate on nematic liquid crystal plasmonic optical modulator and tunable dual-band ‘perfect’ absorbers using asymmetric gold nano-disk array with an overlayer of aligned NLC [2]; the tuning of the optical properties of these nano-structures can be effected by a variety of mechanisms, including electrode-free all-optical means. In the case of optical tuning, our recent studies have demonstrated the possibility of sub-microseconds – nanoseconds switching speed, which is more than 1000 times faster than conventional liquid crystal electro-optics [3, 4].

Reference:

1. I. C. Khoo, “Nonlinear Optics of Liquid Crystalline Materials,” Physics Report 471, pp. 221-267 [2009]. See also, I. C. Khoo, “Extreme nonlinear optics of nematic liquid crystals,” J. Opt. Soc. Am. B28, pp. A45-A55 (2011). Invited paper in Focus Issue dedicated to 50th Anniversary of Nonlinear Optics.

2. Smalley Joseph S. T et al “High contrast modulation of plasmonic signals using nanoscale dual-frequency liquid crystals,” Opt. Express 19, Pages: 15265-15274 (2011); See also Zhang Bingxin et al “Polarization-independent dual-band infrared perfect absorber based on a metal-dielectric-metal elliptical nanodisk array,” Opt. Express 19 Pages: 15221-15228 (2011); Yanhui et al and I. C. Khoo, “Light-driven tunable dual band absorber with liquid-crystal-plasmonic asymmetric nanodisk array ,” Opt. Letts. In Press (2012)

3. I. C. Khoo et al “Ultrafast All-Optical Switching with Transparent and Absorptive Nematic Liquid Crystals-Implications in Tunable Metamaterials,” Mol. Cryst. Liq. Cryst. 543 pp. 151-159 (2011); I. C. Khoo et al “Microseconds-Nanoseconds All-Optical Switching of Visible-Near Infrared (0.5 ?m-1.55 ?m) Lasers with Dye-Doped Nematic Liquid Crystals ,” Mole. Cryst. Liq. Cryst. 527, pp. 109-118 (2010).

4. I. C. Khoo, J. H. Park, J. D. Liou, “Theory and experimental studies of all-optical transmission switching in a twist-alignment dye-doped nematic liquid crystal,” J. Opt. Soc. Am. B25, pp. 1931-1937 (2008).

Bibliography of Prof. I. C. Khoo

I. C. Khoo received the M. A. and Ph.D. degree in Physics from the University of Rochester in 1973 and 1976, respectively. He currently holds the William E. Leonhard Endowed Professor of Electrical Engineering. He is the principal author of over 500 technical publications, 12 invited book chapters, and the author, co-author/editor of 7 books. Awards and honors he received include The Pennsylvania State Engineering Society [PSES] Outstanding Research Faculty Award, the 1998 Faculty Scholar Medal for Outstanding Achievements in Physical Science and Engineering, OSA Fellow, PSES Premier Research Award, IEEE Fellow, and UK Institute of Physics Fellow award. He was the Vice President of Technical Affair for IEEE-Photonics Society in 2001-2004, and Chair of the US Advisory Committee/Int. Commission for Optics of the US National Academies of Science and Engineering in 2008-2010.

In the talk, I will present the so-called stabilization where the total ionization yield decreases once the laser intensity exceeds a certain value. I will discuss the details of the stabilization phenomena by analyzing the photoelectron spectrum which is more sensitive characteristic and bears various signatures of dynamics not revealed by the total ionization probability.