Radiation Effects & Defects in Solids Vol. 163, No. 3, March 2008, 223–228 Spectral, electrical and thermal properties of electron-irradiated L-threonine single crystals G. Ramesh Kumar a , S. Gokul Raj a , K.A. Bogle b , S.D. Dhole b , V.N. Bhoraskar b and R. Mohan a * a Department of Physics, Presidency College, Chepauk, Chennai, Tamil Nadu, India; b Department of Physics, University of Pune, Pune, Maharashtra, India (Received 25 October 2007; final version received 11 February 2008 ) Electrons of energy 6 MeV have been irradiated on L-threonine single crystals. Crystals irradiated at various electron fluences were subjected to various techniques such as Fourier transform infrared spectroscopy, dielectric and Kurtz–Perry powder second harmonic generation analyses. Differential scanning calorimetry measurement has also been carried out to test the thermal stability of the irradiated samples. The results have been discussed in detail. Keywords: NLO crystal; electron irradiation; dielectric permittivity; FTIR spectrum 1. Introduction Nonlinear optical materials play a major role in the technology of photonics. With the advent of lasers, much progress has been made in the field of nonlinear optics. Among the nonlinear optical processes, one of the most visually dramatic features is frequency doubling. In the field of optical information storage, this process can provide for the conversion of near-infrared laser light from diode lasers into deep blue light (1). The other nonlinear phenomena such as frequency mixing, electro-optic modulation and degenerate four-wave mixing are important in the field of optical image storage and optical communication. In this view, organic amino acid single crystals like L-arginine phosphate (2), L-histidine tetrafluoroborate (3) and L-threonine have been extensively studied. In general, amino acid crystals have special features like wide transparency in UV as well as in visible range like non-centrosymmetric, good thermal and mechanical strength (4), which are the essential criterion for second harmonic generation (SHG) applications. In particular, L-threonine is an uncharged neutral amino acid possessing two asymmetric carbon atoms, and it shows greater SHG efficiency than the standard potassium dihydrogen phosphate crystals (5). High-energy electron irradiation produces electronic excitation/ionization in solids, which leads to many changes in its physical properties. It is known that when an electron beam passes through a *Corresponding author. Email: professormohan@yahoo.co.in ISSN 1042-0150 print/ISSN 1029-4953 online © 2008 Taylor & Francis DOI: 10.1080/10420150801979471 http://www.informaworld.com