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Polycrystalline samples of oxides of the general formula LiM(V)M(VI)O(6) (M(V) = Nb, Ta; M(VI) = Mo, W), crystallizing in a non-centrosymmetric (space group P (4) over bar 2(1)m) trirutile structure, exhibit second harmonic generation (SHG) of 1064 nm radiation with efficiencies 15-45 times that of alpha-quartz; interestingly, the SHG response is retained by the protonated derivatives HM(V)M(VI)O(6) . xH(2)O, and their n-alkylamine intercalates as well.

Several transition metal phosphates of the general formula $KM_{0.5}M'_{0.5}OPO_4$, where $M = Nb^v$ or $Ta^v$ and $M' = Ti^{III}, V^{III}, Cr^{III}, Fe^{III}$, possessing the $KTiOPO_4$ (KTP) structure have been synthesized. Unlike KTP, none of these phosphates exhibit second harmonic generation (SHG) of the 1064-nm radiation. Soft-chemical oxidation of the $Ti^{III}$ and $V^{III}$ phosphates using chlorine in $CHCI3$, however, restores the SHG property to the oxidized materials, $K_{0.5}M_{0.5}M'_{0.5}OP0_4 (M = Nb^v, Ta^v; M' = Ti^{Iv}, V^{IV})$. $K_{1-x} Ti_{1-x}V_x OP0_4 (x \leq 0.25)$ prepared similarly from $KTi_{1-x}V_x OPO_4$ also exhibit SHG. The results reveal that exclusive presence of d° cations at the $Ti^{iv}$ site preserves the SHG response of KTP derivatives.

Soft-chemical oxidation of KTiOPO4-like KM(0.5)(V)Ti(0.5)(III)OPO(4) (M = Nb, Ta) using chlorine in CHCl3 is accompanied by partial deintercalation of potassium, yielding K(0.5)MV(0.5)Ti(0.5)(IV)OPO(4) compounds which are new non-linear optical materials that exhibit efficient second-harmonic generation of 1064 nm radiation, as does KTiOPO4.

We report some new results of optical phase conjugation(OPC) studies on three halogenated methanes by stimulated Brillouin scattering (SBS) technique using the second harmonic of pulsed Nd:YAG laser which have not been examined so far.The calculated and experimentally determined SBS gains have been compared. Phase conjugate reflectivities of the order of 70% have been obtained at a pressure as low as 1 bar.

The development of optical phase conjugation using thermally formed gratings in absorbing media, especially the dye solutions, has besides the high efficiencies, many other characteristics which are worthy of study. Here the wavelength depcndence of phase conjugate reflectivity in relation to absorption spectrum of rhodamine-6G and rhodamine-B in water, methanol and ethanol is reported. Further the Bragg condition has been verified for the dominant diffracted beam which shows that the thermal'grating behaves like an optically thick grating.