Sampad Mukherjee

Ultrasonic study of (CuO)x(TeO2)1−x glass system

Abstract Ultrasonic velocity and attenuation in copper–tellurite glasses of different compositions were measured in the temperature range 80–300 K. For the samples with CuO content less than 20 mol% a remarkable change in the behaviour of ultrasonic properties is observed with temperature. However, for the sample having more than 20 mol% of CuO no such changes occur. These changes in behaviour are attributed to the structural change in coordination polyhedron which are induced as the controllable parameters, namely, temperature and composition are varied.

Significant enhancement of the electroactive β-phase of PVDF by incorporating hydrothermally synthesized copper oxide nanoparticles

The influence of copper oxide nanoparticles (CONPs) on the polymorphism of poly(vinylidene fluoride) (PVDF) was systematically investigated in this work. Copper oxide nanoparticles having an average diameter of 60 nm were synthesized by a simple, cost effective, environmentally benign modified hydrothermal method. Then a series of copper oxide nanoparticles incorporating flexible, self-standing PVDF films were prepared by the solution casting technique. The impact of the CONP loading on the structural and morphological properties of PVDF were studied by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy techniques. The thermal properties of the sample were investigated by differential thermal analysis, thermogravimetric analysis and differential scanning calorimetry techniques. The incorporation of CONPs leads to faster crystallization and thereby promotes the formation of electroactive β-phase enriched PVDF films. Strong interfacial interactions between the negatively charged nanoparticle surface and positively charged –CH2 dipoles of the PVDF lead to a significant enhancement of the electroactive β-phase. The 5 wt% CONP–PVDF composite film exhibits a maximum β-phase fraction of 90% due to having the highest interfacial area between the well-dispersed nanoparticles’ surfaces and the polymer.

Non-destructive characterization of zirconia-toughened alumina ceramics using ultrasonics

Ultrasonics has been used for the characterization of sintered zirconia-toughened alumina (ZTA) ceramics. The variation of ultrasonic velocity with volume fraction of zirconia in an alumina matrix was studied. Variation of ultrasonic velocity with volume fraction of ZrO2 content was analysed in terms of a second-degree polynomial in the volume fraction of ZrO2. The elastic moduli and Poissons ratio evaluated from the longitudinal and shear velocities have also been described in terms of a similar equation. The observed variation in velocity and moduli with porosity has been compared with the predicted values based on elasticity theory.

GeO2 nanorods: synthesis, structural and photoluminescence properties

One-dimensional (1D) GeO2 nanorods with smooth surface and uniform diameter throughout their length, are synthesized at a relatively lower temperature by hydrothermal technique in the presence of aluminum foil. Further, the nanorods are doped with rare earth element erbium. The products are characterized by XRD, HRTEM, EDS, FTIR, PL techniques. Synthesized nanorods with diameter in the range ~60–100 nm have core–shell type structure. HRTEM and EDS results reveal that the crystalline core is made by hexagonal α-quartz type GeO2 and amorphous shell contains compound of Al, Ge and O2. The role of this amorphous outer layer for unidirectional growth of the nanorods is discussed in detail. PL study reveals that the synthesized nanorods are capable of emitting a strong band in the violet–blue region. Furthermore, the product can emit light in the green and red region. The Er-doped nanorods also show luminescence around 1533 nm under non-resonant excitation confirming the successful inclusion of Er3+ ions in the nanorods. Consequently, the as-synthesized materials can be potentially used in a nano-luminescent device in a broad spectrum and as a material of the core in an optical fiber amplifier.

Nonlinear pulse reshaping in a designed erbium-doped fiber amplifier with a multicladded index profile

A multicladded normally dispersive erbium-doped fiber amplifier (ND-EDFA) is designed for a short length to operate at the wavelength of 1550 nm with a dispersion of −6.5 ps∕kmnm and parabolic pulse gener- ation through the proposed fiber is studied. The proposed ND-EDFA shows a flattened gain spectrum in C-band. The nonlinear Schrodinger equation is solved numerically in presence of fiber gain, nonlinearity, and dispersion to investigate the pulse propagation through the proposed fiber. While continuous wave (CW) sources are considered, parabolic self- similar pulses with structure factor of 0.072 are created at suitable values of optimum fiber length when input pulse properties and fiber parameters are optimized accordingly. Side by side with a low repetition rate laser source, the pulse propagation equation is controlled by the gain dispersion term and dipole relaxation time, such that the evolution of Gaussian pulses may lead to nonparabolic regime. The effects of pulse parameters like power level, pulse width, and dipole relaxation time on the propagation of input Gaussian pulses through the so-designed ND-EDFA are investi- gated. Our results depict that the pulses with same input energy reshape into exactly parabolic shape for CW laser source or nonparabolic profile for

Parabolic and semiparabolic pulse dynamics in optical fibers

Abstract. Nonlinear pulse dynamics in two stages of different active or passive fibers are investigated in this work. Numerical approach of the symmetrized split step Fourier method is used to solve the nonlinear Schrödinger equation in the presence of fiber gain, nonlinearity, and dispersion. An input Gaussian pulse evolves into a linearly chirped perfect parabolic pulse (PP) when it propagates through a standard normal dispersion decreasing fiber amplifier. At the same time, for an erbium-doped dispersion decreasing fiber amplifier with a similar dispersion variation with length, the semiparabolic pulse (SPP) is produced at the output end of the fiber. To our knowledge, this is shown for the first time. In second stage, the so-obtained perfect PP, SPP, and also a chirp-free perfect PP are fed into the input of several normal dispersion fibers and the comparative pulse evolution is studied in detail with the variations of dispersion coefficient, gain, and nonlinearity. While using these pulses as the input of an anomalous dispersion fiber, our result shows that the linearly chirped PP is most efficient for compressing the pulses with a good quality factor without dropping significant pedestal energy.

Ultrasonic velocity and absorption in (V2O5)x(GeO2)y(P2O5)1-x-y glasses

The velocity and attenuation of longitudinal and transverse ultrasonic waves in four different compositions of (V2O5)x (GeO2)y (P2O5)1-x -y glass system with P2O5 concentration ranging from 2.85 to 15.44 mol% have been measured at temperatures between 80 and 300 K using the ultrasonic pulse echo technique at 8 MHz. The results indicate that for low concentration of GeO2 (y 0.5) velocity variation shows a minimum. The attenuation shows broad high temperature relaxation peak for all samples.

Crack Growth in Castable Refractory due to Thermal Shock Fatigue: An Acousto-Ultrasonic Study

Thermal shock fatigue crack growth in an alumino-silicate castable refractory has been studied using the non-destructive method of acousto-uitrasonic signal analysis. Acousto-ultra- sonic signal parameters supported by strength measurement studies and microscopic observations, indicated initiation, growth and interlinking of microcracks with increasing cycles of thermal shock fatigue. Equations have been proposed to monitor degradation of strength from acousto-uitrasonic measurements. The study reveals that acousto-ultrasonics is a very useful approach for non-destructive qualitative as well as quantitative evaluation of thermal shock damage in refractories.

Efficient parabolic similariton geneartion by third order dispersion compensation

Self-similar parabolic pulse generation is studied for a designed fiber having a high value of third order dispersion (TOD) so that the effect of TOD can be realized in the proposed fiber. As TOD destroys the pulse shape leading to optical wave breaking, a compensation method for TOD in practical fibers is extremely needed. In this paper, the deleterious effect of TOD is efficiently compensated by introducing the time reversal system in self-similar parabolic pulse formation and as a result linearly chirped parabolic pulses are obtained even in presence of high value of TOD.

Comparative study of measured attenuation with the Rayleigh region scattering theory

The study of ultrasonic attenuation by a non-destructive method has an important role in characterizing the mechanical behaviour of different types of materials. The values of sound absorption coefficient (attenuation) of sintered magnesium aluminosilicate glass powder at different frequencies have been measured by the pulse echo method and the data were fitted considering Rayleigh region scattering. Because the sample consists of two phases, one glass and the other ceramic (cordierite), the value of the scattering coefficient can be calculated from the theory by considering a two-phase medium and this value can be compared with that from the Rayleigh region scattering part. The two values of the scattering coefficient are in fair agreement.