The two-photon absorption coefficient and Kerr coefficient of bulk crystalline silicon are determined near the telecommunication wavelengths of 1.3 and 1.55 μm using femtosecond pulses and a balanced Z-scan technique. A phase shift sensitivity of the order of 1 mrad is achieved, enabling the accurate measurement of third-order nonlinear coefficients at fluences smaller than 100 μJ/cm2. From the two-photon absorption coefficient (β∼0.8 cm/GW) and the Kerr coefficient (n2∼4×10−14 cm2/W) at a wavelength λ=1.54 μm, a value F∼0.35 for the nonlinear figure of merit for all-optical switching is determined.

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Third-order nonlinearities in silicon at telecom wavelengths

Optical absorption of tris thiourea zinc sulphate (ZTS) single crystals has been measured and its direct band gap was found to be 3.6 eV. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearties of ZTS have been investigated by Z-scan technique with He-Ne laser at 632.8 nm. The nonlinear refractive index, absorption coefficient and third order susceptibility is found to be in the order of –5.36 ± 0.26 × 10–12 cm2/W, 4.24 ± 0.21 × 10–4 cm/W, 3.5 ± 0.17 × 10–4 esu respectively. Thus optical characterization of ZTS reveals the various industrial application oriented properties of the material. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Linear and nonlinear optical properties of tris thiourea zinc sulphate single crystals

Many intermetallics, such as Ag3Sn, AuSn4, Cu3Sn, Cu6Sn5 (η and η`), Ni3Sn4, and γ–Cu5Zn8 are present in modern solder interconnects as a result of solder chemistry and/or due to the interfacial reaction between solder and metallization scheme. Coarse-grained, single-phase intermetallics are produced by conventional casting followed by annealing for long time. Ambient temperature isotropic elastic moduli (bulk, Young’s, shear, and Poisson’s ratio) and selected plastic properties (hardness and indentation fracture toughness) of these intermetallics are presented. The isotropic elastic moduli of these intermetallics are determined by the pulse-echo technique. The measured bulk, Young’s and shear moduli lie in the range of 6.3 to 11.4 × 1010 N/m2, 7.1 to 12.3 × 1010 N/m2 and 2.7 to 4.5 × 1010 N/m2, respectively. The hardness and fracture toughness are determined by an indentation method. The loads used for indentation experiments were: 100–10,000 g for Ag3Sn and γ–Cu5Zn8, 10–50 g for AuSn4, 200–1000 g for Cu3Sn, 50–100 g for Cu6Sn5, and 100–200 g for Ni3Sn4. The measured Vickers hardness lies in the range of 50 to 470 Kg/mm2, and the measured indentation fracture toughness lies in the range of 2.5 to 5.7 MPa m1/2. Due to coarse grain size of the specimens, the indentation cracks were contained within one grain. In Cu3Sn, Cu6Sn5 (η and η`) and Ni3Sn4 intermetallics, the indentation cracks were found to be nearly straight and run along the indent diagonal. However, the cracks in AuSn4 showed significant zig-zag and branching phenomena, and they seemed to propagate along particular cleavage plane(s). The presence of slip bands are also observed in AuSn4, Ag3Sn, Cu3Sn, γ-Cu5Zn8, and Ni3Sn4. In the case of Ag3Sn and γ–Cu5Zn8, indentation cracks cannot be induced by applying loads up to 10 kg. Rather, extensive plastic deformation occurs resulting in the formation of a large number of shear/kink bands, and possibly twins, that spread across several grains. At a load of 5000 g or higher, Ag3Sn exhibits grain boundary decohesion near the indents. Among the intermetallics studied, Ag3Sn is shown to be the most ductile.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400088713

Elastic properties, hardness, and indentation fracture toughness of intermetallics relevant to electronic packaging

Quantum mechanical, spectroscopic and docking studies of 2-Amino-3-bromo-5-nitropyridine by Density Functional Method

Accumulated thermal effect (ATE), which can be an artifact in femtosecond closed-aperture Z-scan measurements, was investigated by varying the repetition rate of the incident pulse for a dye solution in CHCl3. It was found that the measurement is affected by two-photon-absorption-induced ATE, even at a low repetition rate of 1 kHz. The relaxation time of the ATE was found to be tens of milliseconds by time-resolved thermal-lens experiments and simulations, which is consistent with the observed repetition-rate dependence of the Z-scan measurements. The simulations for various commonly used solvents also exhibited that the ATE can be prominent in hydrocarbon and halogenated hydrocarbon solvents and inconspicuous in alcohols and water.

Two-photon-absorption-induced accumulated thermal effect on femtosecond Z-scan experiments studied with time-resolved thermal-lens spectrometry and its simulation

We demonstrate a novel use of the pump-probe thermal lens spectroscopy and Z-scan techniques for the measurement of the small absorption coefficient in a semiorganic, nonlinear optical crystal zinc (tris) thiourea sulphate. We measure the absorption spectrum and the absolute values of the absorption of the crystal in the near-infrared region (700–980 nm). A maximum absorption coefficient of ∼0.04 cm-1 is reported.

Pump-probe thermal lens near-infrared spectroscopy and Z-scan study of zinc (tris) thiourea sulfate

We report on a detailed study of laser damage in a semiorganic nonlinear optical crystal, zinc (tris) thiourea sulfate using eight nanosecond laser pulses with a repetition rate of 10 Hz at wavelengths of 532 and 1064 nm. The damage morphology shows a correlation with the mechanical hardness anisotropy. The crystal shows a damage threshold measured to be 0.6±0.1 GW/cm2 for a single 532 nm laser pulse which reduces to 0.12±0.01 GW/cm2 as the number of shots is increased to 10 000. Single shot laser damage at 1064 nm wavelength shows an onset estimated to be about 3 GW/cm2. Multiple shots at 1064 nm result in laser ablation hindering the determination of a damage threshold. We suggest a possible role of negative thermal effects resulting in the high damage threshold observed in this crystal.

Laser damage studies in zinc (tris) thiourea sulfate: Nonlinear optical crystal

The Vickers hardness indentations on the two major habit planes (100) and (001) of the solution grown ZTS crystal have been carried out at various azimuthal orientations of the indentor, keeping other variables constant. The observed anisotropic variations have been explained on the basis of effective resolved shear stress on the active slip system in the crystal. The detailed results are reported in the paper.

Sonal Gupte

Papers

Pump-probe thermal lens near-infrared spectroscopy and Z-scan study of zinc (tris) thiourea sulfate

Laser damage studies in zinc (tris) thiourea sulfate: Nonlinear optical crystal

Vickers Hardness Anisotropy and Slip System in Zinc (Tris) Thiourea Sulphate Crystals