title: Second harmonic generation from the 'centrosymmetric' crystals.
abstract: Second harmonic generation (SHG) is a well known non-linear optical phenomena which can be observed only in non-centrosymmetric crystals due to non-zero hyperpolarizability. In the current work we observed SHG from a Zn(II) complex which was originally thought to have crystallized in the centrosymmetric space group C2/c. This has been attributed to the unequal antiparallel packing of the metal complexes in the non-symmetric space group Cc or residual non-centrosymmetry in C2/c giving rise to polarizability leading to strong SHG. The enhancement of SHG by UV light has been attributed to the increase in non-centrosymmetry and hence polarity of packing due to strain induced in the crystals. The SHG signals measured from these crystals were as large as potassium dihydrogen phosphate crystals, KH2PO4 (KDP), and showed temperature dependence. The highest SHG efficiency was observed at 50 K. The SHG phenomenon was observed at broad wavelengths ranging from visible to below-red in these crystals.
authors.affiliation: Centre for Disruptive Photonic Technologies, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Venkatram
authors.initials: V
authors.lastname: Nalla
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Raghavender
authors.initials: R
authors.lastname: Medishetty
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Zhaozhi
authors.initials: Z
authors.lastname: Bai
authors.affiliation: Centre for Disruptive Photonic Technologies, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Handong
authors.initials: H
authors.lastname: Sun
authors.affiliation: Department of Physics, National University of Singapore , 3 Science Drive 3, Singapore 117542, Singapore.
authors.forename: Ji
authors.initials: J
authors.lastname: Wei
authors.affiliation: Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Jagadese J
authors.initials: JJ
authors.lastname: Vittal
keywords: centrosymmetric crystals; second harmonic generation