Interferometric fidelity of self-pumped phase conjugation in BaTiO3 and a four-wave mixing set-up with Bi12SiO20 using nanosecond pulses

Abstract

The fidelity of a self-pumped phase conjugating mirror (SPPCM) in the so-called cat configuration is studied with an interferometric method for a cobalt-doped barium titanate crystal (BaTiO₃:Co) under pulse illumination (8 ns, 532 nm). With this SPPCM a phase conjugating four-wave mixing set-up using the sillenite-type crystal Bi₁₂SiO₂₀ (BSO) was realized. It is shown that the fidelity of both phase conjugating processes under pulse illumination nearly reaches the fidelity of continuous-wave experiments.     

Fracture of anodic-bonded silicon-thin film glass-silicon triple stacks

In this study we focus on the fracture behavior of two types silicon-thin film glass-silicon (Si-Glass-Si) triple stacks specimens with a sharp corner. We determine the notch stress intensity factor Kⁿ for both specimens using a combination of the Williams eigenfunction expansion method, Stroh’s sextic formalism, finite element analysis, and the path-independent H-integral. Empirical solutions of dimensionless stress intensity factors are proposed for two typical specimens, and the dependence of geometry is analyzed. Furthermore, the effect of glass thickness on stress intensity is explored for anodic-bonded Si-Glass-Si triple stacks. We discuss the feasibility of using a critical value of Kⁿ to correlate the failure results for both specimens with various bond area and glass thickness.     

Generation of self-pumped phase conjugation from the -c face of BaTiO3 with femtosecond pulses

We demonstrate a new configuration of self-pumped phase conjugation in BaTiO(3) with 450-nm femtosecond pulses. The pump beam enters the -c face of the crystal at an acute angle with respect to the +c axis. This geometry is different from all known geometries of self-pumped phase conjugations in BaTiO(3). Phase-conjugate reflectivity of 1.7% and a rise time of ~24 s are obtained at an average pump power of 10 mW. The ability of the phase conjugator to serve phase distortions correctly is demonstrated. We propose that the femtosecond phase conjugator operate with the hologram mechanism sharing as the double phase conjugator. The self-pumped phase-conjugate pulses are analyzed by femtosecond electric-field cross correlation.     

A phase-conjugate Twyman-Green interferometer with increased sensitivity for laser beam collimation

Abstract

A Twyman-Green interferometer having a phase-conjugate mirror in one arm and double mirror in another arm is described to measure divergence and to check the collimation of a laser beam. It uses an internally self-pumped phase conjugation in BaTiO₃ crystal as phase-conjugate mirror. The use of double mirror gives a dual interference field which results in improved sensitivity in collimation testing. The dual-field interferogram is also useful in easily distinguishing between the divergent and convergent nature of the test beam. Measurement results are presented.     

Stress intensity factor analysis at an interfacial corner between anisotropic bimaterials under thermal stress

A numerical method using a path-independent H-integral based on the Betti reciprocal principle was developed to analyze the stress intensity factors of an interfacial corner between anisotropic bimaterials under thermal stress. According to the theory of linear elasticity, asymptotic stress near the tip of a sharp interfacial corner is generally singular as a result of a mismatch of the materials’ elastic constants. The eigenvalues and the eigenfunctions are obtained using the Williams eigenfunction method, which depends on the materials’ properties and the geometry of an interfacial corner. The order of the singularity related to the eigenvalue is real, complex or power-logarithmic. The amplitudes of the singular stress terms can be calculated using the H-integral. The stress and displacement fields around an interfacial corner for the H-integral are obtained using finite element analysis. A proposed definition of the stress intensity factors of an interfacial corner involves a smooth expansion of the stress intensity factors of an interfacial crack between dissimilar materials. The asymptotic solutions of stress and displacement around an interfacial corner are uniquely obtained using these stress intensity factors.     

High Reflectivity Broad Band Self-pumped Phase Conjugator at Near Infrared Wavelengths Using SBN : Ce

Abstract

A high reflectivity broad-band SBN : Ce phase conjugator with an external ring cavity in the near infrared wavelength region, 706 to 830 nm, is reported. Phase conjugation reflectivity was measured to be greater than 60% in the wavelength region, 706-820 nm, and as high as 67% at 716 nm. To our knowledge, this is the highest phase conjugation reflectivity by a SBN : Ce self-pumped phase conjugator. Both c.w. and square-wave pump sources were used. No significant changes of the phase conjugation reflectivity were observed when the pump source was changed from c.w. to a square wave at each different wavelength. The wave form of the phase conjugate wave follows the pump square wave. The build-up time of the phase conjugate wave under a square-wave pump was found to be twice that under a c.w. pump when the peak power of the square wave was the same as the power of the c.w. beam.     

White Light Phase-conjugate Lensless Image Projection

Abstract

The lensless projection in white light of images with ～ 30 µ;m resolution has been demonstrated using phase-conjugate reflections from a self-pumped BaTiO₃ crystal which was simultaneously illuminated with red, green and blue laser light. The relative beam incident intensities were crucial in reducing holographic photoerasure and cross-talk effects.     

Analysis of a short interfacial crack from the corner of a rectangular inclusion

A useful method is proposed to analyze a short interfacial crack emanating from the corner of a rectangular inclusion. We first analyze the singular stress field (and the corresponding singularity intensity factor H) without the crack in an infinite medium having the rectangular inclusion. The singular stress field (and the corresponding stress intensity factor K) at the tip of the short interfacial crack lying in the interface of the rectangular inclusion is also analyzed, giving the relation between H and K. With this relation, the stress intensity factor K is easily obtained for the case of a short interfacial crack from the corner of a different rectangular inclusion with different external boundary. This method is based on the assumption that the singular K-field is embedded in another singular H-field, which is much smaller than the specimen geometry. To meet the assumption, it is found here that the eigenfunction corresponding to the next smallest eigenvalue of the singular H-field has to be considered. An example is presented to show the usefulness of the present method, where a short interfacial crack from the corner of a rectangular lead frame in epoxy compound used in electronic packaging is analyzed. It is found that the result of the present method is in good agreement with that of the well-known method.     

Stress intensity factors for coalescing and single corner flaws along a hole bore in a plate

The objective of this paper is to describe the effects of crack interaction on stress intensity factors for two symmetric coplanar corner flaws located along a hole bore. This numerical analysis employes the Finite Element-Alternating Method to determine Mode I stress intensity factors for single and coalescing corner flaws. Using single flaw stress intensity factors as a reference, analysis of crack size and shape effects on $\text{K}{}_{\mathrm{I}}$ for coalescing corner flaws indicates the stress intensity factor for crack points along the hole bore increases as the crack tip separation distance decreases. Interaction effects are not experienced by hole bore crack points when the crack tip separation distance is equal to or greater than half of the largest corner flaw dimension.     

Photorefractive-crystal shape-parameter influence on formation of self-pumped phase conjugation

The influence of crystal-shape parameters on formation of self-pumped phase conjugation is studied experimentally. The parallelism of two c-cut faces of a barium strontium potassium niobate crystal of cuboid shape is changed to control the internal oscillation and thus to induce or to suppress the generation of self-pumped phase conjugation.     

The orientational phase transition at a vortex in3He-B

The orientational phase transition in the vicinity of a single vortex in³He-B is studied. It is the phase transition from a uniformn-texture withn parallel to the magnetic field and the vortex line to ann-texture that is nonuniform near the vortex. The problem of the instability of the the uniformn-texture is equivalent to the quantum mechanical two-dimensional problem of a bound state in a field with an attractive potential 1/r ². The orientational phase transition at a vortex array is also considered. In the limit of large vortex density the orientational phase transition transforms to the phase transition studied by Gongadze et al. The theoretical results are compared with the observed phase transition at a vortex in³He-B.     

Holographic interferometers with photorefractive recording media

We discuss two types of holographic interferometer that contain photorefractive recording media. The first type contains two beams interacting in a photorefractive medium. The second type utilizes a single beam and relies on self-pumped phase conjugation from a photorefractive crystal to make phase changes appear as intensity changes. We show both theoretically and experimentally that the first type can be analyzed in a straightforward manner; however, the second type cannot be approximated as simply a special case of the first type, as one may n?ively suspect.     

Variations of stress intensity factor of a semi-elliptical surface crack subjected to mixed mode loading

Maximum stress intensity factors of a surface crack usually appear at the deepest point of the crack, or a certain point along crack front near the free surface depending on the aspect ratio of the crack. However, generally it has been difficult to obtain smooth distributions of stress intensity factors along the crack front accurately due to the effect of corner point singularity. It is known that the stress singularity at a corner point where the front of 3 D cracks intersect free surface is depend on Poisson's ratio and different from the one of ordinary crack. In this paper, a singular integral equation method is applied to calculate the stress intensity factor along crack front of a 3-D semi-elliptical surface crack in a semi-infinite body under mixed mode loading. The body force method is used to formulate the problem as a system of singular integral equations with singularities of the form r ⁻³ using the stress field induced by a force doublet in a semi-infinite body as fundamental solution. In the numerical calculation, unknown body force densities are approximated by using fundamental density functions and polynomials. The results show that the present method yields smooth variations of mixed modes stress intensity factors along the crack front accurately. Distributions of stress intensity factors are indicated in tables and figures with varying the elliptical shape and Poisson's ratio.     

The passive <Emphasis Type="Italic">Q</Emphasis>-switching regime in a solid state laser with a multiloop cavity

A compact, pulsed-periodic YAG: Nd³⁺ laser with self-pumped phase-conjugate multiloop cavity and passive Q-switching by YAG: Cr4+ and GSGG: Cr4+ crystals has been studied. It is established that the energy and temporal parameters of radiation in separate pulses of a periodic train can be controlled almost without changing the pulse train energy. A regime of generating modulated radiation pulses with a peak power of up to 30 MW and a spatial brightness of 1.7 × 10¹⁵ W/(cm² sr) at a radiation beam quality parameter of M ² < 1.2 has been realized in experiment.     

Fracture initiation at sharp notches under mode I, mode II, and mild mixed mode loading

In the context of linear elasticity, a stress singularity of the type Kⁿr^δ(δ<0) may exist at sharp re-entrant corners, with an intensity Kⁿ. In general the order of the stress singularity δ and the stress intensity differ for symmetric (mode I) and antisymmetric (mode II) loading. Under general mixed-mode loadings, the magnitudes of the mode I and II intensities fully characterize the stress state in the region of the corner. A failure criterion based on critical values of these intensities may be appropriate in situations where the region around the corner dominated by the singular fields is large compared to intrinsic flaw sizes, inelastic zones, and fracture process zone sizes. We determined the mode I and II stress intensities for notched mode I tensile specimens and notched mode II flexure specimens using a combination of the Williams (1952) asymptotic method, dimensional considerations, and detailed finite element analysis. We carried out a companion experimental study to extract critical values of the mode I and II stress intensities for a series of notched polymethyl methacrylate (PMMA) tensile and flexure specimens with notch angles of 90-. The data show that excellent failure correlation is obtained, in both mode I and II loading, through the use of a single parameter, the critical stress intensity. We then analyzed and tested a series of T-shaped structures containing 90- corners. The applied tensile loading results in mixed-mode loading of the 90- corners. Failure of the specimens is brittle and can be well-correlated with a critical mode I stress intensity criterion using the results of the notched mode I tensile tests. This is attributed to large difference in the strength of the stress singularities in modes I and II: δ= -0.4555 and -0.0915 for modes I and II for a 90- notch. As a result, the mode I loading dominates the failure process for the 90- corner in the T-structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Microstructural changes during annealing of cast Ni–Cr–Hf alloys

Abstract

In order to gain knowledge of the nickel–rich corner of the Ni–Cr–Hf phase diagram, microstructures of cast alloys and their evolution towards equilibrium conditions have been followed by optical and scanning electron microscopy, microprobe analysis, and quantitative metallography. The evolution of as–cast microstructures involves the development of a Ni₅Hf plate–like precipitate in two–phase alloys, and various morphological changes in three–phase alloys. As–cast structures are compared with those obtained by arc melting. Direct processing of the scanning electron microscope image has proved to be a valuable tool for microstructural characterization of the transforming phases.

MST/349     

Phase transformations and phase equilibria in Ti -25V -N system at 1200°C

Abstract

The nature of phase transformations and phase equilibria in the Ti- V - N system with about 20 at.-%V and 11 -15 at.-%N has been studied at 1200°C. The results obtained for the titanium rich corner of the Ti - V- N phase diagram provide new information on phase coexistence and the composition of particular phases in this system. Thermodynamic calculations, based on the use of thermodynamic parameters from the three binary subsystems, together with newly assessed thermodynamic parameters published previously, were carried out. Reasonable agreement was obtained between the experiment and the calculations.     

Effect of joint stiffness on peel strength of diffusion bonded joints between Al–Li 8090 alloy sheet

Abstract

The peel behaviour of diffusion bonded joints between Al–Li 8090 alloy sheet depends upon joint geometry, sheet thickness, and the local stiffness of the bonded joint. The local stiffness was increased by bonding 8090 metal matrix composite onto the faces of the joint. At the superplastic forming temperature of 530°C the peel strengths of solid state or liquid phase diffusion bonded joints at peak load were increased from 5–7 N mm^?1 to >8 N mm^?1. This led to superplastic deformation of the sheet without peel fracture at the bonded joint. After air cooling and aging, the corresponding room temperature peel strengths were 174–252 N mm^?1, compared with 30–54 N mm^?1 for an unstiffened joint, an increase by a factor of 3·2–8·4. It was concluded that stiffened bonded joints would enable multiple thin sheet structures to be manufactured in Al–Li 8090 alloy via a diffusion bonding/superplastic forming (DB/SPF) technique. A DB/SPF technique for a three sheet structure is described.

MST/1687     

Higher-generation Schrödinger cat states in cavity QED

Abstract

Higher-generation Schrödinger cat states of the quantized electromagnetic field can be produced in a high-Q cavity, starting from a coherent state, through the passage of prepared Rydberg atoms interacting dispersively across it. These states are natural generalizations of the even and odd coherent states, the N ^th-generations corresponding to specific superpositions of 2 ^N states on a circle in phase space with well defined parity, and present very peculiar properties. Their photon statistics interchange between super- and sub-Poissonian behaviours and the nature of the photon bunching oscillates as the field intensity in the cavity is varied. For higher-generation even states, the minimum value of the Mandel factor almost reaches ?1.0 and the state represents the Fock state |2 ^N ). Squeezing properties and the Wigner function of these higher-generation Schrödinger cat states are also considered.     

Comparative Investigation of Elastic Diffuse Neutron Scattering in C60 Powder

Abstract

C₆₀ powder samples of varying impurity content have been investigated by neutron scattering techniques. For Q > 2.5 Å^?1 (Q = transferred momentum) strong elastic diffuse scattering is found below T_c ~ 260 K providing evidence of static disorder in the low temperature phase. The elastic scattering increases on cooling from T_c to 150 K but remains virtually constant below this temperature. There is no marked dependence on the impurity level. For Q > 2.5 Å^?1 elastic diffuse scattering obeying a sin(QR)/(QR) law is observed both above and below the phase transition (R= radius of C₆₀ molecule). This scattering is nearly independent of temperature, however, depends strongly on the amount of impurities in the sample. In order to account for the unusually strong elastic diffuse scattering intensity model calculations have been performed which relate orientational disorder in C₆₀ to the elastic scattering observed in powder samples.