Наносистемы: физика, химия, математика, Dec 23, 2018
The effects of 2D tunneling bifurcations for quasi-one-dimensional and quasi-two-dimensional Au-q... more The effects of 2D tunneling bifurcations for quasi-one-dimensional and quasi-two-dimensional Au-quantum dot (QD) arrays in thin dielectric films in an external electric field have been studied theoretically and experimentally by Conductive Atomic Force Microscopy (CAFM). In the case of quasi-one-dimensional Au-QD structures (with the QD size ∼ 5 nm), in a dielectric film, a single break under positive bias polarity, corresponding to the effect of 2D tunneling bifurcation, previously predicted theoretically by our team [1], has been detected in experimental I-V curves of the CAFM probe-to-sample contact. A convincing qualitative agreement between the obtained experimental I-V curves and the theoretical field dependence for the 2D-dissipative tunneling probability in the model 2D-oscillator potential has been obtained for the case of parallel tunneling in the weak-dissipation limit at a finite temperature in an external electric field. In the case of quasi-two-dimensional structures with Au QD (with the QD sizes of 2 to 5 nm), possessing metamaterial properties, a pair of kinks corresponding to the double effect of 2D-tunneling bifurcations has been detected on the experimental I-V curves. A qualitative agreement between the experimental I-V curves and the theoretical field dependence for the 2D-dissipative tunneling probability has been obtained for a situation with an effectively "negative" permittivity of the heat bath.
we propose a novel metamaterial Perfect absorber at terahertz frequency for fast and non-destruct... more we propose a novel metamaterial Perfect absorber at terahertz frequency for fast and non-destructive detection of microorganisms. The sensor provides possibilities for obtaining dielectric information of microorganisms, which are of great potential for future biomedical applications.
This paper presents a scheme to achieve THz radiation by the beating of two laser beams in a plas... more This paper presents a scheme to achieve THz radiation by the beating of two laser beams in a plasma. Lasers are obliquely incident on an underdense plasma with density ripples. Lasers having different frequencies and wave numbers but the same electric fields exert a ponderomotive force on the plasma electrons at the beating frequency which creates THz waves. The general formulas for the efficiency and THz field amplitude with arbitrary laser beam profiles (such as super-Gaussian and triangular) are derived where the effect of electron-neutral collisions is taken into account. The results show that the efficiency of THz radiation is sensitive to the angle of incidence, beam profile, collision frequency, and beating frequency. The most striking feature of this paper is that with obliquely incident laser beams, higher efficiency can be reached for collisionless and collisional plasma compared to normal incidence.
36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Jul 24, 2000
The various physical processes, arising due to the interaction of a diverging plasma jet from a h... more The various physical processes, arising due to the interaction of a diverging plasma jet from a hollow cathode and the applied convergent magnetic field within the coupling plasma zone of an electrostatic ion thruster, have been considered. The transport of the electrons in the direction of the baffle annulus is mainly through the loss cone associated with mirror type plasma that exists within the coupling plasma zone. The resultant electric E-field vector within the coupling plasma zone varies in both magnitude and direction along the axial z-direction. Plasma oscillations, due to the interaction of a discharge plasma column and a longitudinal B-field, produces an electric field which in turn gives rise to anomalous electron drift across the Bfield. Inherent wide-band electrical noise in the hollow cathode acting as a primary source for the plasma coupling zone, give rise to random fluctuations in charge density, and this also leads to instability within the coupling plasma zone. In the presence of negative space charge accumulation in the vicinity of the baffle disc and with an enhanced applied radial electric field, the electron flow is predominantly aligned in the direction of the baffle annulus. The profile of the equipotentials in the vicinity of the baffle annulus is convex and the electrons converge due to the electrostatic lens effect. The plasma electron mean free path is of the order of 1.3 crn and the energy of the electrons due to drift along the resultant E-field is approximately 24 eV.
We report a scheme to generate radially polarized THz radiation by frequency difference of Hermit... more We report a scheme to generate radially polarized THz radiation by frequency difference of Hermite Cosh Gaussian lasers in hot electron, collisional and density modulated plasma. The effect of laser (spatial field distribution) and plasma parameters (plasma density structure, electron-neutral collisions and electron temperature) on emitted THz field profile is investigated. We found that THz field profile varies with spatial intensity profile of pump lasers. The THz amplitude increases with the pump laser intensity gradient. Our investigations show that electron collisions attenuate the THz amplitude without affecting the THz field profile. The highest THz field and conversion efficiency are obtained at resonance condition i.e. 1 − 2 ≈. Off-resonant excitation of THz radiation is also observed with less THz amplitude. Our investigations also reveal that the value of THz-field peak and efficiency increase monotonically with electron thermal velocity (electron temperature). A high THz field (~GV/m) and conversion efficiency ~0.08 can be obtained for optimized pump laser and plasma parameters.
We report a theoretical model of radially polarized terahertz (THz) wave emission by nonlinear mi... more We report a theoretical model of radially polarized terahertz (THz) wave emission by nonlinear mixing of bicolor, radially polarized lasers having a top-hat envelope profile [s (profile index)≥1] in density modulated hot plasma. We investigate the effect of the laser profile index on the emitted THz field profile and found that THz field amplitude and peak location changes with the laser profile index. Our numerical investigations show that THz field amplitude is the highest around ωp≈ω1−ω2 (where ωp is the plasma frequency and ω1 and ω2 are the laser frequencies). We observe that phase matching can be achieved with the help of the plasma density modulation wave number. The plasma density modulation wave number increases with electron temperature and decreases with the frequency mismatch between ωp and ω1−ω2. We found that the conversion efficiency is maximum at ω1−ω2≈ωp and increases fivefold with an increase in electron thermal velocity (vth) from vth=0 to vth=0.2c, where c is the speed of light.
Abstract We propose a theoretical model to produce ultra-intense and ultra-compressed laser pulse... more Abstract We propose a theoretical model to produce ultra-intense and ultra-compressed laser pulses based on Stimulated Brillouin Scattering (SBS) process. The amplification of laser pulses via Brillouin amplification process is obtained when three waves (two transverse electromagnetic waves and a longitudinal plasma wave) couple in the plasma when resonance condition for energy (frequency ω ) and momentum (wave-vector k ) is satisfied. Counter propagating seed pulse takes energy from laser pulse when they interact with each other via the process of stimulated Brillouin scattering and finally it gets amplified and compressed. We optimize the parameters (like initial plasma density, initial laser pulse intensity, interaction time, wave breaking time, fillamentation time etc.) for SBS compression and amplification to obtain high intensity laser pulse. This optimized window exactly match with the simulation results reported by Weber et al. [1]. Due to strong SBS within the optimum parametric window, one can develop compact plasma-based amplifier, which can produce high intensity short laser pulse. This technique offers damage less amplification of laser pulses. The amplification and compression ratio obtained in this model are 94 and 30, respectively. These intensities can be used as seed intensities to obtain Zetta watt laser pulses using C-3 (Cascade, Conversion and Compression) technique reported by Mourou et al. [2].
The spectrum of energy and angle of emittance of the electrons generated during ionization of neo... more The spectrum of energy and angle of emittance of the electrons generated during ionization of neon ions Ne 8þ , krypton ions Kr 32þ , and argon ions Ar 16þ by a laser pulse have been obtained for different values of laser frequency chirp and normalized laser pulse duration. The energy of the electron beam shifts to higher energy with the introduction of frequency chirp. The energy peak shifts towards lower energy with an increase in frequency chirp, and the electron beam becomes more quasi-monoenergetic. The energy peak shifts to higher energy with decreasing laser pulse duration due to increase in asymmetry of the pulse, however, the quasi-monoenergetic property of the electron beam decreases. We can obtain MeV, MeV/GeV, and GeV electron beams using neon, krypton, and argon gases as target. The scattering of the electrons decreases with decreasing laser pulse duration and increasing laser intensity. The energy peak is sharper and at higher energy for the ions located after laser focus than that for the ions located before laser focus for a tightly focused laser pulse.
The acceleration of electrons generated during ionization of low density gases has been studied u... more The acceleration of electrons generated during ionization of low density gases has been studied using seventh order correction fields of a laser pulse for linearly and circularly polarized laser pulse. The spectrum of energy and angle of emittance of the electrons generated and accelerated during ionization of nitrogen ions N5+, oxygen ions O6+, neon ions Ne8+, krypton ions Kr32+, and argon ions Ar16+ has been obtained for normalized laser intensity parameter a0=4, 6, 12, 20, and 75, respectively, for normalized laser spot size r0=60, 90, and 120. Energy and scattering spectrum for nitrogen, oxygen, and neon ions show two peaks and may generate quasimonoenergetic beams for small laser spot sizes. The energy spectrum is wide and peak lies at low energy for krypton than that for argon. The energy peaks are at higher energy for circularly polarized laser pulse than that for linearly polarized laser pulse. The paraxial approximation may fail to yield accurate results at low values of laser spot size and high laser intensity. The energy associated with spectrum peak tends to saturate with laser intensity.
Наносистемы: физика, химия, математика, Oct 30, 2020
In the zero-range potential model and in the effective mass approximation, dispersion equations h... more In the zero-range potential model and in the effective mass approximation, dispersion equations have been obtained, that describe dependence of the average binding energies of the quasistationary g-and u-states of the D − 2-center in the QD, as well as the widths of energy levels on the magnitude of the external electric field and the parameters of 1D-dissipative tunneling. Dips in the field dependences of the binding energies average values for quasi-stationary g-and u-states have been revealed. It is shown that the field dependences of the energy level widths for the g-and u-states of the D − 2-center have a resonance structure at the external electric field strengths corresponding to the dips in the field dependences of the average binding energies. In the dipole approximation, the field dependence of the probability of the electron radiative transition from a quasistationary u-state to a quasi-stationary g-state of the D − 2-center in a QD in the presence of dissipative tunneling with the participation of two local phonon modes has been calculated. It was found that the curve of the radiative transition probability (RTP) dependence on the strength of the external electric field contains three peaks.
We have investigated the effect of initial phase on error in electron energy obtained using parax... more We have investigated the effect of initial phase on error in electron energy obtained using paraxial approximation to study electron acceleration by a focused laser pulse in vacuum using a three dimensional test-particle simulation code. The error is obtained by comparing the energy of the electron for paraxial approximation and seventh-order correction description of the fields of Gaussian laser. The paraxial approximation predicts wrong laser divergence and wrong electron escape time from the pulse which leads to prediction of higher energy. The error shows strong phase dependence for the electrons lying along the axis of the laser for linearly polarized laser pulse. The relative error may be significant for some specific values of initial phase even at moderate values of laser spot sizes. The error does not show initial phase dependence for a circularly laser pulse. V
In this article, we present the differential rotational profile of extreme ultraviolet (EUV) coro... more In this article, we present the differential rotational profile of extreme ultraviolet (EUV) corona. For this purpose, we used observations with high resolution obtained from SDO/AIA at 19.3-nm wavelength from years 2011 to 2021. We found the higher rotation rate of the equatorial segment (14.8 deg d−1) which drops about 13.5 deg d−1 on both sides of the poles. The average rotation rate (i.e. from 2011 to 2021) of the equatorial region of EUV corona is found to be higher than that of the photosphere, chromosphere, transition region, and corona. Furthermore, the average rotational gradient (as a function of latitude) of the EUV corona is lower than that of the photosphere and transition region. Interestingly, we found a significant correlation of the hemispheric rotational asymmetry with the solar activity indicator (SSNs) and EUV emission. The cross-correlation analysis indicates that the hemispheric rotational asymmetry leads the solar activity indicator (SSN) and EUV emission by a...
Наносистемы: физика, химия, математика, Dec 23, 2018
The effects of 2D tunneling bifurcations for quasi-one-dimensional and quasi-two-dimensional Au-q... more The effects of 2D tunneling bifurcations for quasi-one-dimensional and quasi-two-dimensional Au-quantum dot (QD) arrays in thin dielectric films in an external electric field have been studied theoretically and experimentally by Conductive Atomic Force Microscopy (CAFM). In the case of quasi-one-dimensional Au-QD structures (with the QD size ∼ 5 nm), in a dielectric film, a single break under positive bias polarity, corresponding to the effect of 2D tunneling bifurcation, previously predicted theoretically by our team [1], has been detected in experimental I-V curves of the CAFM probe-to-sample contact. A convincing qualitative agreement between the obtained experimental I-V curves and the theoretical field dependence for the 2D-dissipative tunneling probability in the model 2D-oscillator potential has been obtained for the case of parallel tunneling in the weak-dissipation limit at a finite temperature in an external electric field. In the case of quasi-two-dimensional structures with Au QD (with the QD sizes of 2 to 5 nm), possessing metamaterial properties, a pair of kinks corresponding to the double effect of 2D-tunneling bifurcations has been detected on the experimental I-V curves. A qualitative agreement between the experimental I-V curves and the theoretical field dependence for the 2D-dissipative tunneling probability has been obtained for a situation with an effectively "negative" permittivity of the heat bath.
we propose a novel metamaterial Perfect absorber at terahertz frequency for fast and non-destruct... more we propose a novel metamaterial Perfect absorber at terahertz frequency for fast and non-destructive detection of microorganisms. The sensor provides possibilities for obtaining dielectric information of microorganisms, which are of great potential for future biomedical applications.
This paper presents a scheme to achieve THz radiation by the beating of two laser beams in a plas... more This paper presents a scheme to achieve THz radiation by the beating of two laser beams in a plasma. Lasers are obliquely incident on an underdense plasma with density ripples. Lasers having different frequencies and wave numbers but the same electric fields exert a ponderomotive force on the plasma electrons at the beating frequency which creates THz waves. The general formulas for the efficiency and THz field amplitude with arbitrary laser beam profiles (such as super-Gaussian and triangular) are derived where the effect of electron-neutral collisions is taken into account. The results show that the efficiency of THz radiation is sensitive to the angle of incidence, beam profile, collision frequency, and beating frequency. The most striking feature of this paper is that with obliquely incident laser beams, higher efficiency can be reached for collisionless and collisional plasma compared to normal incidence.
36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Jul 24, 2000
The various physical processes, arising due to the interaction of a diverging plasma jet from a h... more The various physical processes, arising due to the interaction of a diverging plasma jet from a hollow cathode and the applied convergent magnetic field within the coupling plasma zone of an electrostatic ion thruster, have been considered. The transport of the electrons in the direction of the baffle annulus is mainly through the loss cone associated with mirror type plasma that exists within the coupling plasma zone. The resultant electric E-field vector within the coupling plasma zone varies in both magnitude and direction along the axial z-direction. Plasma oscillations, due to the interaction of a discharge plasma column and a longitudinal B-field, produces an electric field which in turn gives rise to anomalous electron drift across the Bfield. Inherent wide-band electrical noise in the hollow cathode acting as a primary source for the plasma coupling zone, give rise to random fluctuations in charge density, and this also leads to instability within the coupling plasma zone. In the presence of negative space charge accumulation in the vicinity of the baffle disc and with an enhanced applied radial electric field, the electron flow is predominantly aligned in the direction of the baffle annulus. The profile of the equipotentials in the vicinity of the baffle annulus is convex and the electrons converge due to the electrostatic lens effect. The plasma electron mean free path is of the order of 1.3 crn and the energy of the electrons due to drift along the resultant E-field is approximately 24 eV.
We report a scheme to generate radially polarized THz radiation by frequency difference of Hermit... more We report a scheme to generate radially polarized THz radiation by frequency difference of Hermite Cosh Gaussian lasers in hot electron, collisional and density modulated plasma. The effect of laser (spatial field distribution) and plasma parameters (plasma density structure, electron-neutral collisions and electron temperature) on emitted THz field profile is investigated. We found that THz field profile varies with spatial intensity profile of pump lasers. The THz amplitude increases with the pump laser intensity gradient. Our investigations show that electron collisions attenuate the THz amplitude without affecting the THz field profile. The highest THz field and conversion efficiency are obtained at resonance condition i.e. 1 − 2 ≈. Off-resonant excitation of THz radiation is also observed with less THz amplitude. Our investigations also reveal that the value of THz-field peak and efficiency increase monotonically with electron thermal velocity (electron temperature). A high THz field (~GV/m) and conversion efficiency ~0.08 can be obtained for optimized pump laser and plasma parameters.
We report a theoretical model of radially polarized terahertz (THz) wave emission by nonlinear mi... more We report a theoretical model of radially polarized terahertz (THz) wave emission by nonlinear mixing of bicolor, radially polarized lasers having a top-hat envelope profile [s (profile index)≥1] in density modulated hot plasma. We investigate the effect of the laser profile index on the emitted THz field profile and found that THz field amplitude and peak location changes with the laser profile index. Our numerical investigations show that THz field amplitude is the highest around ωp≈ω1−ω2 (where ωp is the plasma frequency and ω1 and ω2 are the laser frequencies). We observe that phase matching can be achieved with the help of the plasma density modulation wave number. The plasma density modulation wave number increases with electron temperature and decreases with the frequency mismatch between ωp and ω1−ω2. We found that the conversion efficiency is maximum at ω1−ω2≈ωp and increases fivefold with an increase in electron thermal velocity (vth) from vth=0 to vth=0.2c, where c is the speed of light.
Abstract We propose a theoretical model to produce ultra-intense and ultra-compressed laser pulse... more Abstract We propose a theoretical model to produce ultra-intense and ultra-compressed laser pulses based on Stimulated Brillouin Scattering (SBS) process. The amplification of laser pulses via Brillouin amplification process is obtained when three waves (two transverse electromagnetic waves and a longitudinal plasma wave) couple in the plasma when resonance condition for energy (frequency ω ) and momentum (wave-vector k ) is satisfied. Counter propagating seed pulse takes energy from laser pulse when they interact with each other via the process of stimulated Brillouin scattering and finally it gets amplified and compressed. We optimize the parameters (like initial plasma density, initial laser pulse intensity, interaction time, wave breaking time, fillamentation time etc.) for SBS compression and amplification to obtain high intensity laser pulse. This optimized window exactly match with the simulation results reported by Weber et al. [1]. Due to strong SBS within the optimum parametric window, one can develop compact plasma-based amplifier, which can produce high intensity short laser pulse. This technique offers damage less amplification of laser pulses. The amplification and compression ratio obtained in this model are 94 and 30, respectively. These intensities can be used as seed intensities to obtain Zetta watt laser pulses using C-3 (Cascade, Conversion and Compression) technique reported by Mourou et al. [2].
The spectrum of energy and angle of emittance of the electrons generated during ionization of neo... more The spectrum of energy and angle of emittance of the electrons generated during ionization of neon ions Ne 8þ , krypton ions Kr 32þ , and argon ions Ar 16þ by a laser pulse have been obtained for different values of laser frequency chirp and normalized laser pulse duration. The energy of the electron beam shifts to higher energy with the introduction of frequency chirp. The energy peak shifts towards lower energy with an increase in frequency chirp, and the electron beam becomes more quasi-monoenergetic. The energy peak shifts to higher energy with decreasing laser pulse duration due to increase in asymmetry of the pulse, however, the quasi-monoenergetic property of the electron beam decreases. We can obtain MeV, MeV/GeV, and GeV electron beams using neon, krypton, and argon gases as target. The scattering of the electrons decreases with decreasing laser pulse duration and increasing laser intensity. The energy peak is sharper and at higher energy for the ions located after laser focus than that for the ions located before laser focus for a tightly focused laser pulse.
The acceleration of electrons generated during ionization of low density gases has been studied u... more The acceleration of electrons generated during ionization of low density gases has been studied using seventh order correction fields of a laser pulse for linearly and circularly polarized laser pulse. The spectrum of energy and angle of emittance of the electrons generated and accelerated during ionization of nitrogen ions N5+, oxygen ions O6+, neon ions Ne8+, krypton ions Kr32+, and argon ions Ar16+ has been obtained for normalized laser intensity parameter a0=4, 6, 12, 20, and 75, respectively, for normalized laser spot size r0=60, 90, and 120. Energy and scattering spectrum for nitrogen, oxygen, and neon ions show two peaks and may generate quasimonoenergetic beams for small laser spot sizes. The energy spectrum is wide and peak lies at low energy for krypton than that for argon. The energy peaks are at higher energy for circularly polarized laser pulse than that for linearly polarized laser pulse. The paraxial approximation may fail to yield accurate results at low values of laser spot size and high laser intensity. The energy associated with spectrum peak tends to saturate with laser intensity.
Наносистемы: физика, химия, математика, Oct 30, 2020
In the zero-range potential model and in the effective mass approximation, dispersion equations h... more In the zero-range potential model and in the effective mass approximation, dispersion equations have been obtained, that describe dependence of the average binding energies of the quasistationary g-and u-states of the D − 2-center in the QD, as well as the widths of energy levels on the magnitude of the external electric field and the parameters of 1D-dissipative tunneling. Dips in the field dependences of the binding energies average values for quasi-stationary g-and u-states have been revealed. It is shown that the field dependences of the energy level widths for the g-and u-states of the D − 2-center have a resonance structure at the external electric field strengths corresponding to the dips in the field dependences of the average binding energies. In the dipole approximation, the field dependence of the probability of the electron radiative transition from a quasistationary u-state to a quasi-stationary g-state of the D − 2-center in a QD in the presence of dissipative tunneling with the participation of two local phonon modes has been calculated. It was found that the curve of the radiative transition probability (RTP) dependence on the strength of the external electric field contains three peaks.
We have investigated the effect of initial phase on error in electron energy obtained using parax... more We have investigated the effect of initial phase on error in electron energy obtained using paraxial approximation to study electron acceleration by a focused laser pulse in vacuum using a three dimensional test-particle simulation code. The error is obtained by comparing the energy of the electron for paraxial approximation and seventh-order correction description of the fields of Gaussian laser. The paraxial approximation predicts wrong laser divergence and wrong electron escape time from the pulse which leads to prediction of higher energy. The error shows strong phase dependence for the electrons lying along the axis of the laser for linearly polarized laser pulse. The relative error may be significant for some specific values of initial phase even at moderate values of laser spot sizes. The error does not show initial phase dependence for a circularly laser pulse. V
In this article, we present the differential rotational profile of extreme ultraviolet (EUV) coro... more In this article, we present the differential rotational profile of extreme ultraviolet (EUV) corona. For this purpose, we used observations with high resolution obtained from SDO/AIA at 19.3-nm wavelength from years 2011 to 2021. We found the higher rotation rate of the equatorial segment (14.8 deg d−1) which drops about 13.5 deg d−1 on both sides of the poles. The average rotation rate (i.e. from 2011 to 2021) of the equatorial region of EUV corona is found to be higher than that of the photosphere, chromosphere, transition region, and corona. Furthermore, the average rotational gradient (as a function of latitude) of the EUV corona is lower than that of the photosphere and transition region. Interestingly, we found a significant correlation of the hemispheric rotational asymmetry with the solar activity indicator (SSNs) and EUV emission. The cross-correlation analysis indicates that the hemispheric rotational asymmetry leads the solar activity indicator (SSN) and EUV emission by a...
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