AN INVESTIGATION INTO NEW NLO PHOSPHATES. Reeve, W. F., Clarendon Laboratory, Physics Department, Oxford University, England

As interest increases in optical technology, so the need grows for new nonlinear crystals with widely varying properties. For many years scientists have used materials from the phosphate series for use as frequency converters. Indeed, two of the most well known, and commercially successful nonlinear optical (NLO) materials come from the phosphate series, namely potassium titanyl phosphate^(l) (KTiOPO₄ or KTP) and potassium dihydrogen phosphate⁽²⁾ (KH₂PO₄ or KDP). Given the success of both these materials, it seems worthwhile to investigate the phosphate family further.

A preliminary report is given on the theoretical models used in determining structural guide-lines in a systematic search for new NLO phosphates. The screening procedure used for identifying possible materials from structural databases, such as examining structural geometry, is summarised. A description is given of the initial testing for second-harmonic generation efficiency using the Kurtz⁽³⁾ test and the later more accurate single-crystal NLO analysis based on that developed by Velsko⁽⁴⁾. Early results are presented on the XYPO₄ (where X=Li, Na, Rb and Y=Pb, Ca, Sr, Ba) family, including a description of material preparation, X-ray diffraction analysis and NLO properties, including phase-matchability and average effective nonlinearity.

It is hoped that this new investigation into phosphates may produce further new NLO materials with different capabilities needed in future optical technology, and also, when analysed with accurate structure determinations, may also help in furthering our knowledge of NLO structure-property relationships. This would not only enable more accurate structural guidelines for further searches to be established, but also increase the probability of improving already commercially used materials.

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