We report the experimental investigation of nonlinear cascaded lasing χ(3) ↔ χ(2) effects in UV and visible ranges and high-order Stokes and anti-Stokes generation covering spectral space of about 18000 cm-1 by stimulated Raman scattering and multi-wave mixing processes under one-micron picosecond pumping in the paraelectric state of NH4H2PO4 and ND4D2PO4 single crystals. All recorded Raman induced laser wavelengths are identified and attributed to their SRS-promoting vibration modes. Brief review of nonlinear-laser processes in non-centrosymmetric phosphates of KH2PO4-family and some physical properties of NH4H2PO4 and ND4D2PO4 are given as well.

https://iopscience.iop.org/article/10.1002/lapl.200810032/pdf

Nonlinear-laser effects in NH4H2PO4 (ADP) and ND4D2PO4 (DADP) single crystals: Almost two-octave multi-wavelength Stokes and anti-Stokes combs, cascaded lasing in UV and visible ranges with the involving of the second and third harmonic generation

Aspects of symmetry and crystal chemistry of the linear electrooptic effect are analyzed on the basis of new experimental results. Relations between the linear electro-optic effect [rσijk] (unclamped) and the linear electrostrictive effect [dijk] are investigated by comparison of the longitudinal effects r'111 and d'111; The relation |d'111|max/|r'111|max≥1 is valid for 41 of the hitherto available data of 49 crystals. Guidelines for the search of crystals with high electro-optic effects are reviewed. The most important keywords for a “chemical engineering” of new electro-optic materials are: pyroelectric symmetry groups; “polar” structural units; structures with strongly asymmetric bonds; molecules with high hyperpolarizabilities; structures tending towards a dielectric instability.

Crystallographic aspects of the linear electro-optic effect

The electro-optic path retardations of potassium dihydrogen phosphate (KDP) for various wavelengths are determined experimentally employing a Soleil-Babinet compensator and a constant deviation spectrometer. From these observations the Pockels' constants Flambda , the linear electro-optic constants rij (both clamped and unclamped) and the half-wave voltages Blambda/2 for two different orientations at different wavelengths in the visible region of the spectrum are determined. In the light of the present investigations the sign of the piezoelectric constant d36 is discussed. The results obtained now on KDP are compared with some data available from the literature.

http://iopscience.iop.org/article/10.1088/0022-3719/11/11/024/pdf

Linear electro-optic dispersion in KDP

We have derived analytical relations necessary for interpreting piezooptic effect and calculation of all piezooptic coefficients on the basis of interferometric technique, which take a micro-wedge shape of samples into consideration. The analysis is presented for the tetragonal crystals of point symmetry classes 4, 4 and 4/m. The relations valid for the remaining symmetry classes 422, 4mm, 42m and 4/mmm represent simple particular cases of the general relations.

/pdf/analytical-relations-describing-piezooptic-effect-in-pa25vhrxd8.pdf

Analytical relations describing piezooptic effect in tetragonal crystals

In the present communication all seven stress optical and seven strain optical constants of KDP are reported for the first time at 5890 a. These values are obtained by subjecting a large number of orientations to stress birefringence and ultrasonic studies and by combining this information with other available data by the least squares method. The results are checked from different points of view and are discussed with reference to some of the earlier investigations.

Photoelastic behaviour of KDP

Though a number of authors have reported the photoelastic behaviour of ADP, there are discrepancies in the literature with regard to its photoelastic constants. In the present study all the static and dynamic data have been obtained again by repeating the experiments and the most acceptable values of the stress-optical and strain-optical constants are calculated by the method of least squares. The results are discussed in the light of earlier studies.

Photoelastic constants of ADP

It is shown that a single light intensity measurement does not allow the determination of the sign of the ratio of strain‐optical constants determined ultrasonically. However, if an experiment is performed in which the ratios are overdetermined, it is possible to determine the signs by applying the criterion that the results of the various measurements must be consistent. The equations which must be satisfied for the criterion of consistency are obtained for nine of the 32 crystal classes. The application of the technique is presented with numerical values for the case of NaCl.

T. S. Narasimhamurty

Papers

Photoelastic constants of ADP

Photoelastic behaviour of KDP

Determination of the signs of the ratios of strain‐optical constants measured ultrasonically