Optical rectification in ammonium dihydrogen phosphate, potassium dihydrogen phosphate and quartz

Abstract

Ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ), potassium dihydrogen phosphate (KH 2 PO 4 ) and quartz each have two independent, nonzero, optical rectification coefficients. Measurements of various ratios among these coefficients are described. The uncertainty of ± 6%, achieved in the most favourable case, represents improvement by a factor of 8 over previous relative measurements of optical rectification coefficients by Bass, Franken & Ward (1965). The signs of the coefficients are determined directly for the first time. Improved accuracy makes possible a more stringent test of the theoretical relation between linear electro-optic and optical rectification coefficients which was pointed out by Armstrong, Bloembergen, Ducuing & Pershan (1962) and studied in more detail by Ward & Franken (1964). The data for NH 4 H 2 PO 4 and KH 2 PO 4 are consistent with this relation. It is thought that apparent discrepancies in the case of quartz, where the data are less accurate, are probably explained otherwise than by the breakdown of the relation. The temperature dependences in the range +20 to —120°C of both optical rectification coefficients in KH 2 PO 4 are investigated and interpreted in terms of local field factors. Optical rectification data and other data from the literature for NH 4 H 2 PO 4 , KH 2 PO 4 and quartz are discussed in relation to Kleinman’s symmetry conditions and quantum mechanical expressions for the nonlinear coefficients to yield information on the nature of the underlying processes.