The role of the longitudinal component of the electric field vector in two-wave mixing in photorefractive BaTiO3

It is shown that for waves incident with a polarisation in the plane of the grating the component of the electric field in the direction of propagation must be included in the calculations. Coupled differential equations for both the transverse and longitudinal components are derived for wave interaction in photorefractive BaTiO₃. Analytic solutions for the electric field of the signal wave are obtained under the assumption that the pump wave is undepleted. For the parameters considered the longitudinal component is shown to be negligible.     

Can the electric field gradient probe lattice stability?

The relationship between the electrostatic force acting on the nucleus and the electric field gradient measured by nuclear methods is discussed. Particular attention is paid to the proper application of the Laplace equation. This point is unclear in several standard textbooks on Mössbauer spectroscopy.     

连续波锁模Pr3+:YLF激光器

本文报导了采用氩离子激光器来泵浦Pr³⁺:YLF晶体,应用声光调制器实现了主动锁模;同时应用振动─高反射平面镜也实现了被动锁模,两种锁模均得到了ps光脉冲.据作者了解这是这种晶体材料的第一次锁模运转.     

Higher diffracted orders in a BSO crystal: An experimental study of transients

The emergence of higher diffracted orders when a slightly wedged BSO crystal is illuminated by a single coherent beam is studied with input power and applied voltage as parameters. It is shown that the power spreads gradually towards the higher orders and that the temporal variation of the power in each beam is qualitatively the same as in the case of two-wave interaction.The author is currently with the 86th Military Airlift Squadron, Travis Air Force Base, CA 94535, USA     

Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.     

Mössbauer spectroscopy studies of the magnetic ordering and relaxation of some chemically interesting systems in the Helium-3 temperature range (0.3 K to 1.3 K)

A new carbon sorption pumped Helium-3 Mössbauer spectroscopy cryostat is briefly described. Exempliary spectra for some magnetically interesting iron compounds are presented.Supported by the U.S. National Science Foundation Division of Materials Research—Solid State Chemistry Program Grant No. DMR 8313710.