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Photorefractive nonlinearity in pure...

Chen, Kan.

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Photorefractive nonlinearity in pure and doped liquid crystals.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Photorefractive nonlinearity in pure and doped liquid crystals./
Author:	Chen, Kan.
Description:	189 p.
Notes:	Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3737.
Contained By:	Dissertation Abstracts International69-06B.
Subject:	Engineering, Electronics and Electrical. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3318883
ISBN:	9780549689713

Photorefractive nonlinearity in pure and doped liquid crystals.
Chen, Kan.

Photorefractive nonlinearity in pure and doped liquid crystals. - 189 p.

Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3737.

Thesis (Ph.D.)--The Pennsylvania State University, 2006.

Detailed theoretical analysis and experimental investigation of the photorefractive (PR) effect in liquid crystals (LC) are presented. The photorefractive nonlinearity arises from the formation of spatially modulated space charge field. Two main mechanisms contribute space charge field in liquid crystals. One comes from the formation and the subsequent dissociation of charge transfer complexes between the liquid crystal and the dopant, which produces mobile charge carriers. The generation and redistribution of charge carriers, induced by external dc voltage and inhomogeneous illumination, form the space charge field. Second source comes from the so-called Carr-Helfrich effect, which states that transverse space charge field can be induced by liquid crystal dielectric and conductivity anisotropy under external applied field. Assisted by the space charge field, large optical nonlinearity can be obtained in liquid crystals.

ISBN: 9780549689713Subjects--Topical Terms:

626636
Engineering, Electronics and Electrical.

Photorefractive nonlinearity in pure and doped liquid crystals.
LDR:04664nam 2200325 4500 001 1393823
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008 130515s2006 ||||||||||||||||| ||eng d
020 $a 9780549689713
035 $a (UMI)AAI3318883
035 $a AAI3318883
040 $a UMI $c UMI
100 1 $a Chen, Kan. $3 1672400
245 1 0 $a Photorefractive nonlinearity in pure and doped liquid crystals.
300 $a 189 p.
500 $a Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3737.
500 $a Adviser: Iam-Choon Khoo.
502 $a Thesis (Ph.D.)--The Pennsylvania State University, 2006.
520 $a Detailed theoretical analysis and experimental investigation of the photorefractive (PR) effect in liquid crystals (LC) are presented. The photorefractive nonlinearity arises from the formation of spatially modulated space charge field. Two main mechanisms contribute space charge field in liquid crystals. One comes from the formation and the subsequent dissociation of charge transfer complexes between the liquid crystal and the dopant, which produces mobile charge carriers. The generation and redistribution of charge carriers, induced by external dc voltage and inhomogeneous illumination, form the space charge field. Second source comes from the so-called Carr-Helfrich effect, which states that transverse space charge field can be induced by liquid crystal dielectric and conductivity anisotropy under external applied field. Assisted by the space charge field, large optical nonlinearity can be obtained in liquid crystals.
520 $a Liquid crystal molecular reorientation occurs under the combined action of internal space charge field and external dc field. The subsequent birefringent grating accounts for photorefractive diffraction and beam coupling. Its orientational feature is investigated and evidenced by facts, such as, polarization anisotropy observed in probe diffraction, external threshold behavior, asymmetric two beam coupling, and geometrical dependence of diffraction efficiency.
520 $a In parallel with the effort to understand basic mechanisms governing photorefractive effect in liquid crystals, we've also attempted to enhance PR performance, mainly by chemical doping. The doping effect, both organic (C60, single walled nanotubes (SWNT)), and inorganic doping (e.g., CdSe nanorodes), is studied. Substantial improvement of photorefractive response can be observed in our doping samples, in terms of larger diffraction efficiency and higher beam coupling gain. Although the underline mechanism is still intricate in molecular level, we believe the enhanced photo-charge generation and transport, and/or the enlarged conductivity anisotropy, may be the possible explanations for the better PR performance in doped LC system.
520 $a While there is compelling evidence that liquid crystal reorientation under space charge field is responsible for photorefractive grating formation, much less understood, however, are the mechanisms involved in the formation of space charge fields that drive the orientation. The photorefractive effect in undoped LC samples is revisited, with our focus on the study of space charge field origin. Theoretical models were derived to identify the photorefractive threshold voltage. The PR threshold voltage can be substantially lowered with the increase of incident light intensity, which is mainly due to inhomogeneous interface ions distribution induced surface torque. The thickness dependence of threshold voltage lowing effect was also measured, which allows us to estimate the modulation depth of surface charge. Our result shows both bulk and surface optically induced charges and field modulation are responsible for the build up of space charge field.
520 $a Based on our work, several potential further researches are proposed, which are all related to photorefractive effect, yet fall into three categories. First is to further study doping effect: increase SWNT doping concentration using functionalized nanotubes and try other novel doping materials such as nanometals. Second is to continue the investigation of surface effect in doped LC samples. We anticipate more interesting surface effect exists in doping system. The last one is to study PR effect in new LC composites, such as PSLC (polymer stablilized liquid crystal) and PDLC (polymer dispersed liquid crystal).
590 $a School code: 0176.
650 4 $a Engineering, Electronics and Electrical. $3 626636
650 4 $a Engineering, Materials Science. $3 1017759
690 $a 0544
690 $a 0794
710 2 $a The Pennsylvania State University. $3 699896
773 0 $t Dissertation Abstracts International $g 69-06B.
790 1 0 $a Khoo, Iam-Choon, $e advisor
790 $a 0176
791 $a Ph.D.
792 $a 2006
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3318883