Navneet K. Sharma

Fabrication and characterization of pH sensor based on side polished single mode optical fiber

Abstract Fabrication and characterization of side-polished single mode optical fiber pH sensor utilizing evanescent field absorption spectroscopy and dye doped sol–gel immobilization technology are presented. The sensor is prepared by fixing the fiber in a groove made on one of the surfaces of a fused silica block. To make the surface sensitive to pH it is polished up to the core of the fiber and a film containing a mixture of three pH sensitive dyes is coated on it using sol–gel technology. The influence of the radius of curvature of the groove on the sensitivity of the sensor is studied. The decrease in the radius of curvature of the groove increases the sensitivity. This occurs due to the increase in the evanescent field and hence its interaction with the pH sensitive dyes entrapped in the film. The advantage of the side-polished single mode optical fiber sensor is that only 0.1 ml of sample is sufficient to measure the pH of the fluid. This is important when the procurement of the sample in large quantity is not possible.

Fabrication and Characterization of a Fiber-Optic pH Sensor for the pH Range 2 to 13

Fabrication and characterization of a fiber-optic pH sensor based on evanescent field absorption and immobilization of ethyl violet dye on the unclad core of the fiber using sol-gel technique have been reported. The probe has been demonstrated to operate in the pH range 2 to 13. The operating range is the largest among those reported in the literature by using a single pH-sensitive dye. The sensitivity of the sensor increases with the increase in the length of the probe. The response of the probe depends on the ionic strength and the temperature of the fluid. This suggests that the pH sensor developed by us is likely to perform best under well-defined sample conditions.

Strong terahertz radiation generation by beating of two x-mode spatial triangular lasers in magnetized plasma

Resonant THz radiation generation is proposed by beating of two spatial-triangular laser pulses of different frequencies (ω1, ω2) and wave numbers ( k1, k2) in plasma having external static magnetic field. Laser pulses co-propagating perpendicular to a dc magnetic field exert a nonlinear ponderomotive force on plasma electrons, imparting them an oscillatory velocity with finite transverse and longitudinal components. Oscillatory plasma electrons couple with periodic density ripples n ′ = nq0e iqz to produce a nonlinear current, i.e., responsible for resonantly driving terahertz radiation at (ω = ω1 − ω2, k = k1 − k2 + q). Effects of THz wave frequency, laser beam width, density ripples, and applied magnetic field are studied for the efficient THz radiation generation. The frequency and amplitude of THz radiation were observed to be better tuned by varying dc magnetic field strength and parameters of density ripples (amplitude and periodicity). An efficiency about 0.02 is achieved for laser intensity of 2 × 10 W/cm in a plasma having density ripples about 30%, plasma frequency about 1 THz and magnetic field about 100 kG.

Higher order antibunching in intermediate states

Since the introduction of binomial state as an intermediate state, different intermediate states have been proposed. Different nonclassical effects have also been reported in these intermediate states. But till now higher order antibunching is predicted in only one type of intermediate state, which is known as shadowed negative binomial state. Recently we have shown that the higher order antibunching is not a rare phenomenon [P. Gupta, P. Pandey, A. Pathak, J. Phys. B 39 (2006) 1137]. To establish our earlier claim further, here we have shown that the higher order antibunching can be seen in different intermediate states, such as binomial state, reciprocal binomial state, hypergeometric state, generalized binomial state, negative binomial state and photon added coherent state. We have studied the possibility of observing the higher order subpoissonian photon statistics in different limits of intermediate states. The effects of different control parameters on the depth of non classicality have also been studied in this connection and it has been shown that the depth of nonclassicality can be tuned by controlling various physical parameters.

Tunable and efficient terahertz radiation generation by photomixing of two super Gaussian laser pulses in a corrugated magnetized plasma

A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies (ω1, ω2) and wave numbers (k→1, k→2) in a performed corrugated plasma embedded with transverse dc magnetic field. Lasers exert a nonlinear ponderomotive force, imparting an oscillatory velocity to plasma electrons that couples with the density corrugations ( n′=nα0eiαz) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ∼ ωh (upper hybrid frequency). The periodicity of density corrugations is suitably chosen to transfer maximum momentum from lasers to THz radiation at phase matching conditions ω=ω1−ω2 and k→=k→1−k→2+α→. The efficiency, power, beam quality, and tunability of the present scheme exhibit high dependency upon the applied transverse dc magnetic field along with q-indices and beam width parameters ( a0) of super Gaussian lasers. In the present scheme, efficiency ∼10−2 is achieved with the optimization of ...

Growth and field emission characteristics of diamond films on macroporous silicon substrate

The effect of substrate pretreatments such as ultrasonication or scratching by diamond powder on the microstructure and field emission characteristics of diamond grown over silicon and macroporous (anodized) silicon substrates was investigated. These films were grown in a hot filament chemical vapor deposition (CVD) system. Scanning electron microscope (SEM) studies revealed that ultrasonic pretreatment of the substrates increases nucleation density of CVD diamond by two orders of magnitude. Atomic force microscopy and energy dispersive x-ray analysis of the substrates showed that seeding is responsible for the enhanced nucleation density of diamond. SEM study showed that diamond powder scratching of porous silicon leads to uniform coverage of the substrate by the CVD diamond. Cross-sectional SEM showed growth of diamond inside the pores only after pretreating porous silicon with diamond powder. Raman spectroscopy of all the samples showed a scattering peak corresponding to diamond. Discontinuous diamond ...

Stimulated Raman scattering of beat wave of two counter-propagating X-mode lasers in a magnetized plasma

Effects of transverse static magnetic field on stimulated Raman scattering (SRS) of the beat wave excited by two counter-propagating lasers are studied. Two counter-propagating lasers with frequency difference, ω1∼ω2≥2ωp, drive a non resonant space charge beat mode at wave number k→0≈k→1+k→2 in a plasma, where k→1 and k→2 are wave vectors of lasers having frequencies ω1 and ω2, respectively. The driven beat wave acts as a pump for SRS and excites parametrically a pair of plasma wave (ω,k→) and side band electromagnetic wave (ω3,k→3) propagating in the sideward direction in such a way that momentum remains conserved. The growth rate of Raman process is maximum for side scattering at θs=π/2 for lower values of applied magnetic field (∼1 kG), which can be three fold by applying magnetic field ∼5.0 kG. Thus, optimum value of magnetic field can be utilized to achieve maximum electron acceleration in counter propagating geometry of beat wave acceleration by reducing the growth rate of Raman process.

Parametric excitation of fast upper hybrid waves by non-resonant beating of counter-propagating X-mode lasers in a magnetized plasma

Generation of fast and slow upper hybrid waves by two plasmon decay of non-resonant beating mode of two counter-propagating X-mode lasers is modelled in magnetized plasma. Two counter-propagating lasers having frequencies and wave-vectors (ω1,k1) and (ω2,k2), respectively, generate a non resonant beat wave at frequency difference ω0≈ω1∼ω2 and wave number k→0≈k→1+k→2 which parametrically excites a pair of copropagating fast and slow upper hybrid waves at ω0≈2ωh+(3k12vth2/ωh)  (1−ωh/ω1) where ωh and vth are the upper hybrid frequency and electron thermal speed, respectively. The fast upper hybrid wave can be utilized for electron acceleration because its phase velocity is close to c. The growth rate of decay process is Γ∼ωp/10 at scattering angle θs∼5π/6 and magnetic field ∼90  T, which is one order higher as compared to the growth rate of Raman process. The growth rate can be further enhanced (∼20%) by increasing the magnetic field ∼450 T.

Terahertz radiation generation by pulse slippage of Cosh-Gaussian lasers in a corrugated magnetized plasma

The combined effects of pulse slippage and the transverse magnetic field are studied on terahertz radiation excitation by nonlinear beating of two cosh-Gaussian (ChG) laser pulses propagating in a corrugated plasma. The beating lasers exert nonlinear ponderomotive force on plasma electrons. The oscillating electrons couple with corrugations present in the plasma and resonantly excite a nonlinear current (at different frequencies) which drive the terahertz wave at proper phase matching conditions. As the group velocity of THz radiation is higher than the group velocity of beating lasers, the THz pulse slips forward the pump lasers, and its saturation takes place. The effects of THz wave frequency, the decentred parameter (of beating lasers), the periodicity of the density structure, and the applied dc magnetic field are studied on THz emission. An efficiency of ∼10−4 is achieved for a laser intensity of ∼ 2 × 10 15 W/cm2 (at a laser wavelength of ∼10.6 μm for the CO2 laser).

ITO based fiber optic SPR sensor

A surface plasmon resonance (SPR) based fiber optic sensor with ITO layer coated on the core of the optical fiber is presented and theoretically analyzed. It has been shown that the sensitivity of the ITO layer based SPR sensor increases with the increase of ITO layer thickness. Moreover, 290 nm thick ITO layer based SPR sensor possesses high sensitivity of 2485 nm/ RIU.