Manmohan D. Aggarwal

Characterization of polymeric composite films with MWCNT and Ag nanoparticles

Using a solution casting technique, for sample preparation, pyroelectric multi-walled carbon nanotubes in polyvinylidene fluoride composite films have been fabricated, to allow the characterization of both the pyroelectric and dielectric properties of such composites. The properties measured include: (1) dielectric constants and (2) pyroelectric coefficient as a function of temperature. From the foregoing parameters, figures-of-merit, for infrared detection and thermal-vidicons, were calculated. The results indicated figures-of-merit of composite film were higher than pristine polyvinylidene fluoride films. Additionally, composite films, composed of pyroelectric Lithium tantalate [(LiTaO3), LT] ceramic particles and silver nanoparticles incorporated into polyvinylidene fluoride-trifluoroethylene [PVDF-TrFE) 70/30 mol%] copolymer matrix, have been prepared. The results indicate that silver nanoparticles incorporated lithium tantalate:polyvinylidene fluoride-trifluoroethylene composite films may have application for un-cooled infrared sensor.

Photomagnetism and photoluminescence (PL) of (Pb-Fe-e-) complex in lead magnesium niobate-lead titanate (PMN-PT) crystals containing β-PbO nanoclusters

We present electron paramagnetic resonance (EPR)--evidence of photomagnetism under the conditions of in situ green laser illumination (photo-EPR) in lead magnesium niobate-lead titanate, Pb(Mg,Nb)O3-PbTiO3 (PMN-PT), containing nanoparticles/wires of orthorhombic beta-PbO as identified by Raman spectroscopy. Photo-EPR studies of the sample containing beta-PbO, brownish red in color, have shown intense line at g=2.00, and its yield increased when produced in the presence of 7.5 kG external magnetic field suggesting the formation of magnetic polaron. This was identified as due to interaction between Fe3+, photoinduced Pb3+ and unpaired electron trapped at oxygen vacancies. The photoinduced growth and decay of magnetic polaron has shown a non-exponential behavior. Photoluminescence (PL) studies were conducted with excitation at 308 nm (XeCl laser) and also at 454.5, 488 and 514.5 nm using Ar+ laser. The excitation with 308 nm gave broad PL centered at 500 and 710 nm the latter being quite prominent in beta-PbO containing crystals, along with cooperative luminescence at 350 nm involving two emitting centers. The excitation with Ar+ laser lines, close to the electronic absorption in samples containing beta-PbO gave richer and sharp PL emission in red region from the constituents of the magnetic polaron and also intense anti-Stokes emission on excitation with 514.5 nm radiation. This appears to be due to phototransfer optically stimulated luminescence (PT-OSL) involving electron-hole recombination at photoinduced magnetic polaron site.

Photoluminescence, FTIR, and laser-Raman spectroscopic studies of PMN-PT containing iron

Lead magnesium niobate-lead titanate, Pb(Mg, Nb)O3-PbTiO3 is a piezoelectric, ferroelectric crystal at room temperature with large electromechanical coefficient. The crystals were grown by PbO-B2O3 flux method. Typically the crystals were colorless and transparent, but a small fraction of them were Brown/reddish colored and show interesting photoluminescence (PL) properties. The PL studies were conducted under XeCl (308nm) excitation and under Argon Ion (Ar+) laser excitation. The excitation with 308nm gave broad PL centered at 500nm and intense emission at 710nm. The emission at 710nm in colorless crystals is very weak. The excitation with Ar+ laser coinciding with electronic absorption in brown samples gave rich and sharp PL particularly with 514.5 nm excitation. The PL with 514.5nm-Ar+ laserexcitation, consisted of intense anti stokes emission in addition to intense red and near infrared emission, is a result of photo-transfer optically stimulated luminescence (PT-OSL). This involved electron-hole recombination at photoinduced magnetic polaron site. The PL emissions and the centers identified are the followings: 718nm emission due to magnetic polaron and 360nm emission due to cooperative emission from two polarons, Fe-R line at 660nm due to Fe3+ coupled to a cation; 380nm and 399nm due to Pb2+ clusters and Nb5+ center; 630 and 860 nm due to 6p→6s transition of Pb3+ and 760nm due to isolated Fe3+ ions. Raman spectrum of brown samples revealed the presence of nano particles/wires of orthorhombic β PbO. The FTIR spectrum gives evidence of significant amount of hydroxyl impurity.

Stationary temporal solitons in optical fiber and the swing effect of spatial solitons in two-dimensional devices

The one-particle type temporal soliton exists by maintaining a balance between dispersive linear contributions on the one hand and non-linear effects on the other. The linear contributions occur from processes such as group velocity and polarization mode dispersion. The nonlinear features occur from Kerr, or power law non-Kerr behavior. In addition, a variety of perturbations, such as damping, Brillouin scattering, and Raman effects exist to alter the simple soliton solution. In this paper, we review the propagation of temporal solitons in power law non-Kerr media. This is developed through the higher nonlinear Schroedingers equation (HNLSE). Also, the fundamentals of multiple-scales are presented that will be used to yield quasi-stationary solitons when perturbations are present. In waveguides, the one-particle type spatial soliton exists by maintaining a balance between the linear propagational diffraction and non-linear self-focusing, while possibly being subjected to a variety of perturbations. Here, we use a spatial optical soliton solution to the nonlinear Schroedinger equation in an inhomogeneous triangular refractive index profile as a small index perturbation to illustrate the oscillation property within a two dimensional waveguide. We determine, from the motion of spatial soliton, its effective acceleration, period of oscillation, and compare results with the Gaussian refractive index profile. Such spatial solitons behave as point masses existing in a Newtonian gravitational potential hole.

Electrooptic characterization and Czochralski growth technique of pure and doped lithium niobate crystals

Ferroelectric Lithium Niobate (LN) possesses a combination of unique electrooptic, piezoelectric, pyroelectric, and photorefractive properties. These features make it suitable for applications in optical devices-as modulators, switches, and filters in communication systems and holographic recording medium, etc. Here, the growth of lithium Niobate doped with iron and doubly doped with iron and manganese ions will be described. The growth technique will be through Automatic Diameter Control Czochralski Design. From these grown crystals, critical electrooptical coefficients using null detection polarimetry are provided. The results of growth, electrooptic measurements, and some physical properties are compared and presented. Also, the use of doped LN crystals in devices is discussed.

Optical solitons in anisotropic and inhomogeneous media

Short pulse spectral content becomes modified while propagating in dispersive media. However, in dispersive nonlinear media, optical pulses resulting in solitary waves maintain their existence if proper balance is established between nonlinear self-phase modulation on the one hand and linear dispersion on the other. Such invariance pulse shape is critical for data transfer reliability in telecommunication technologies. Robust solitary waves that emerge from collisions unaltered are called solitons. During propagation of optical solitons in inhomogeneous media their trajectories are observed to deviate from straight-line paths to that of oscillatory behavior. Here, we use a spatial optical soliton solution to the nonlinear Schrödinger equation in an inhomogeneous triangular refractive index profile as a small index perturbation to illustrate the oscillation motion. We determine the effective acceleration, give the period of oscillation, and compare results with the Gaussian refractive index profile. Such spatial solitons behave as point masses existing in a Newtonian gravitational potential hole. This novel transverse oscillatory behavior, occurring for various refractive index profiles, results from an effectively bounded acceleration.

Photo-EPR studies of photorefractive BaTiO3 heavily doped with Cr3+: evidence of photo-induced dissociation of Cr3+ dimers

Barium titanate crystals were grown by top seeded solution growth technique, nominally pure and also 0.05% and 1% Cr3+ impurity. We have conducted electron paramagnetic resonance (EPR) and photo-EPR studies at room temperature to investigate the role of Cr3+ impurity in photoinduced electron transfer. Nominally pure crystals contained Fe3+ as impurity, and its EPR is consistent with work reported by previous investigators. The Cr3+ doped crystals also contained Fe3+ impurities. It was observed that the site symmetry and the strength of the axial field parameter for Fe3+ complex were significantly different in Cr3+ doped crystals compared to nominally pure BaTiO3. The EPR spectra of Cr3+ were distinguished using the hyperfine structure of odd isotope 53Cr (I=3/2). By Photo-EPR technique we observe that in the presence of Cr3+, Fe3+ is not significantly photosensitive. In contrast Cr3+ exhibited higher photosensitivity in the presence of Fe3+. This was monitored by locking the magnetic field to 1/2↔1/2 transition of Cr3+, and recording intensity as a function of time, under insitu laser illumination. In lightly doped crystals the intensity of Cr3+ signal is sharply reduced immediately after switching the laser OFF showing non-exponential decay. In heavily doped crystals photo-EPR signal clearly shows that the fast decay of Cr3+ was followed by slow and steady build up of Cr3+ signal. The growth of Cr3+ signal was attributed to photoinduced decoupling of Cr3+ dimers. Thus, by doping BaTiO3 with Cr3+ more efficient grating formation can be achieved and time dependent phenomena are observed.