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The possibility of selective population of the energy levels of quantum systems using a single unipolar subcycle pulse and a pair of pulses has been studied. The possibility of selective population of quantum levels has been clear...
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The possibility of selective population of the energy levels of quantum systems using a single unipolar subcycle pulse and a pair of pulses has been studied. The possibility of selective population of quantum levels has been clearly illustrated based on the numerical solution of a system of equations for the density matrix of a three-level medium that interacts with a pair of subcycle attosecond and terahertz pulses. The possibility of creating a population inversion in a three-level medium using a pair of such pulses has been shown. The dynamics of population gratings in a three-level medium exposed to the action of a pair of Gaussian pulses of large amplitude on the system is studied. Whereas the shape of the gratings in a weak field is harmonic, according to analytical calculations performed by the perturbation theory, in the case of a strong field, the spatial profile of the gratings may differ from the sinusoidal profile and may have a complex structure of peaks.
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Progress in reducing the duration of light pulses (down to one cycle of field oscillations or less), achieved in the last decades, has made it possible to experimentally observe and study a number of atomic-scale phenomena that oc...
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Progress in reducing the duration of light pulses (down to one cycle of field oscillations or less), achieved in the last decades, has made it possible to experimentally observe and study a number of atomic-scale phenomena that occur at ultrafast times. Their study and observation are unavailable with conventional sources of monochromatic laser radiation. When using few- or subcycle pulses, a number of well-known phenomena in optics, which are well studied when using long monochromatic radiation sources, either lose their meaning, or their underlying physical mechanisms require revision. For example, the direct interference of subcycle pulses with their direct overlap is not possible due to their short duration. This note addresses the interference phenomenon, when a pair of subcycle pulses act on a medium, while do not simultaneously overlap inside it. In this case, it is not the pulses themselves that interfere in the medium, but the probability amplitudes of the bound states of the medium. Therefore the result of their impact on the medium can be interpreted as the interference of the areas of pulses-electric pulse areas (integral of the electric field strength over time) and envelope areas (integral of the slowly varying envelope of the electric field strength over time).
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Pulse shaping is an important step in the unfolding-synthesis technique. In this paper we present efficient digital pulse-shaping algorithms that utilize repeated sum polynomials. These algorithms address the most common constrain...
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Pulse shaping is an important step in the unfolding-synthesis technique. In this paper we present efficient digital pulse-shaping algorithms that utilize repeated sum polynomials. These algorithms address the most common constraint in pulse shape synthesis - the finite duration of the pulses. The presented digital methods for efficient real-time synthesis use only basic digital signal processing functions (addition, constant multiplication, and shift), thereby minimizing required signal processing resources. A differentiation technique to decompose pulse shapes defined by polynomials is presented and used to synthesize arbitrary trapezoidal/triangular pulse shapes. The synthesis of rational, exponential, trigonometric and other non-polynomial defined pulse shapes can be approximated in real time. A methodology to approximate non-polynomial defined pulse shapes is described, and Gaussian and sinusoidal pulse shapes are synthesized via polynomial approximation and linear interpolation. The pulse shape synthesis algorithms are presented in recursive form and are suitable for efficient implementation by using integer only arithmetic.
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This paper describes the experiments conducted for the development of a solid state pulse power modulator using low cost Mn-Zn ferrite cores. These ferrite cores although have restricted magnetic parameters, gave promising results...
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This paper describes the experiments conducted for the development of a solid state pulse power modulator using low cost Mn-Zn ferrite cores. These ferrite cores although have restricted magnetic parameters, gave promising results for use in pulsed power systems. The experience gained has revealed that such low cost ferrite can be used in the development of pulse power modulators.
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This paper discusses the experiments conducted for the development of 50 kV, 10 A, 10 ;C;s duration, and rise time of 2 ;C;s solid state pulse power modulator using toroidal amorphous steel core and low cost IGBT switches. The exp...
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This paper discusses the experiments conducted for the development of 50 kV, 10 A, 10 ;C;s duration, and rise time of 2 ;C;s solid state pulse power modulator using toroidal amorphous steel core and low cost IGBT switches. The experiments revealed (i) the need for new design methodologies based on energy transfer between the electrical and magnetic systems and (ii) the success of low-cost switching circuit.
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Shaped pulses designed for broadband excitation, inversion and refocusing are important tools in modern NMR spectroscopy to achieve robust pulse sequences especially in heteronuclear correlation experiments. A large variety of mos...
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Shaped pulses designed for broadband excitation, inversion and refocusing are important tools in modern NMR spectroscopy to achieve robust pulse sequences especially in heteronuclear correlation experiments. A large variety of mostly computer-optimized pulse shapes exist for different desired bandwidths, available rf-field strengths, and tolerance to B_1-inhomogeneity. They are usually derived for a single spin 1/2, neglecting evolution due to J-couplings. While pulses with constant resulting phase are selfcompensated for heteronuclear coupling evolution as long as they are applied exclusively on a single nucleus, the situation changes for concurrently applied pulse shapes. Using the example of a ~1H,~(13)C two spin system, two J-compensated pulse pairs for the application in INEPT-type transfer elements were optimized: a point-to-point pulse sandwich called BEBEtr, consisting of a broadband excitation and time-reversed excitation pulse, and a combined universal rotation and point-to-point pulse pair called BUBI, which acts as a refocusing pulse on ~1H and a corresponding inversion pulse on ~(13)C. After a derivation of quality factors and optimization protocols, a theoretical and experimental comparison with conventionally derived BEBOP, BIBOP, and BURBOP-180° pulses is given. While the overall transfer efficiency of a single pulse pair is only reduced by approximately 0.1%, resulting transfer to undesired coherences is reduced by several percent. In experiments this can lead to undesired phase distortions for pairs of uncompensated pulse shapes and even differences in signal intensities of 5-10% in HSQC and up to 68% in more complex COB-HSQC experiments.
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This article describes a high-current, pulse power inductor design to achieve compactness, robustness, and enhanced energy density. Conventional pulse power inductor designs focus on containing the strong expansive Lorentz forces ...
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This article describes a high-current, pulse power inductor design to achieve compactness, robustness, and enhanced energy density. Conventional pulse power inductor designs focus on containing the strong expansive Lorentz forces on the inductor coil using bulky external housing. The novelty of the present design is the use of a high-conductivity metallic enclosure placed coaxially around the inductor coil which modifies the magnetic field distribution in such a way that the force experienced by the inductor coil is compressive, rather than expansive. Hence, the Lorentz forces on the inductor coil are contained using a strong inner coil former used for holding the coil, thus eliminating the need for a strong external housing. This leads to a more compact inductor design. This inductor design is studied extensively using COMSOL Multiphysics 5.3 and Opera 18R2 for validation of design concept. Based on these simulations, inductors with inductance of 2 mu H and energy density of 5 kJ/l are fabricated and tested successfully on an experimental setup to get a pulsed current of magnitude 250 kA and rise time 82 mu s with two such inductors connected in parallel as load. Based on the experimental experience and confidence gained on these inductors, a design concept of more compact inductor has also been proposed.
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A composite miniature structure used to generate megawatt electrical pulses is described. Two photoconductive switches (one GaAs and the other Si) are used, along with voltage multiplication and pulse forming lines, to generate ov...
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A composite miniature structure used to generate megawatt electrical pulses is described. Two photoconductive switches (one GaAs and the other Si) are used, along with voltage multiplication and pulse forming lines, to generate over 14-kV pulses from a DC bias of only 9 kV. These megawatt pulses have picosecond synchronization and can vary in width from nanoseconds to picoseconds.
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Based on an approximate solution of the Schrodinger equation, the effect that a pair of extremely short small-amplitude subcycle pulses has on a quantum system is studied. It is shown that, if the pulses are shorter than the inver...
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Based on an approximate solution of the Schrodinger equation, the effect that a pair of extremely short small-amplitude subcycle pulses has on a quantum system is studied. It is shown that, if the pulses are shorter than the inverse frequencies of atomic transitions, the probability of transitions between levels is determined by the electric area of the pulses and the time delay between them. As a consequence, a unipolar pulse can more efficiently affect the system than a bipolar one, while a sequence of pulses realizes a selective action on quantum objects, despite a nonresonant character of the interaction.
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90° and 180° universal rotation (UR) pulses are two of the most important classes of pulses in modern NMR spectroscopy. This article presents a systematic study characterizing the achievable performance of these pulses as functi...
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90° and 180° universal rotation (UR) pulses are two of the most important classes of pulses in modern NMR spectroscopy. This article presents a systematic study characterizing the achievable performance of these pulses as functions of bandwidth, pulse length, and tolerance to B1-field inhomogeneity/miscalibration. After an evaluation of different quality factors employed in pulse design algorithms based on optimal control theory, resulting pulses are discussed in detail with a special focus on pulse symmetry. The vast majority of resulting BURBOP (broadband universal rotations by optimal control) pulses are either fully symmetric or have one symmetric and one antisymmetric Cartesian rf component, where the importance of the first symmetry has not been demonstrated yet and the latter one matches the symmetry that results from a previously derived construction principle of universal rotation pulses out of point-to-point pulses [3]. Optimized BURBOP pulses are shown to perform better than previously reported UR pulses, resulting in shorter pulse durations for the same quality of broadband rotations. From a comparison of qualities of effective universal rotations, we find that the application of a single optimal refocusing pulse matches or improves the performance of two consecutive inversion pulses in INEPT-like pulse sequence elements of the same total duration.
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