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

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

The photoelastic (piezo-optic) property of the ferroelectric crystals lithium heptagermanate Li2Ge7O15 (LGO) were studied in para- and ferro-electric phases for different orientations. The value of stress optical coefficient Cijk (in Brewsters) along a, b, c-axes were determined at RT (291 K) and 278 K and were compared with some other ferroelectric systems like Rochelle-salt (RS), potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP). Large photoelastic coefficients and other properties like good mechanical strength, or transition temperature close to RT and stability in ambient environment favour LGO as a potential candidate for photoelastic applications.

Determination of the photoelastic coefficients in lithium heptagermanate crystals

Estimation of the electrooptic Kerr effect in ADP and DKDP crystals

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.

K. Veerabhadra Rao

Papers

Photoelastic constants of ADP