Download (4Mb) - Etheses - Saurashtra University

Chapter I Brief Introduction...
Jagannathan, et al [49] have reported 141 times efficiency of SHG than that of
urea for 4-Dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystals.
DAST has found application in continuously tunable THz and the far infrared
generation system [50]. Azariah et al [51] have found that the SHG efficiency
is 1.24 times that of KDP for n-nitro-4-methoxy benzylidene aniline. Urea has
been studies for several years. It is difficult to grow crystals and the polished
surfaces other than cleavage surfaces which are extremely hygroscopic [52].
Devices based on urea must immerse the crystal in oil, which is usually
absorbing in the UV region [53]. The efforts made to resolve the problems
associated with urea are not very successful.
Organic molecules with π-electron delocalization are currently of wide
interest as NLO materials in optical switches and NLO devices [13]. A large
amount of organic compounds have been studied as NLO materials [14].
Historically, the optical SHG in an organic material was reported for the first
time in 1964 by two research groups in 3, 4-benzopyrene by Rentzepis and
Pao [54] and in hexamethylenetetramine single crystals by Heilmer et al
[55].Two years later, Orlov [56] reported SHG from the hippuric acid. Further
research in organic NLO was stimulated in 1970, when Davydov et al [57]
reported strong SHG from organic compounds having electron donor and
acceptor groups attached to a benzene ring while screening a large variety of
organic compounds using the Kurtz and Perry powder method.
Semi-organic Materials
Semi-organic compounds share the properties of both organic and
inorganic compounds. They are organic based materials in which the
polarizable part is an organic molecule which is stoichiometrically bonded with
25