skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures

Abstract

Our work is based on high harmonic generation in a gaseous medium (helium ion), by exploiting gold bowtie nanostructures as laser field amplifiers. As the result of emission of a laser pulse, the wave function of the atom varies with time; so, it is necessary to solve 1D time-dependent Schrödinger equation by means of split operator method. By illumination of a short duration, long wavelength three color laser pulse inside the gap, the enhanced field not only changes with time, but also varies in space. In this work we considered this space inhomogeneity in linear and nonlinear schemes. We show that in nonlinear case, the plateau region is more extended. We also show that in larger gaps, cutoff occurs on higher frequencies. But limitation of electron motion in bowtie nanostructures leads to the choice of an optimum 16 nm gap size in our case. We predict that, by the superposition of supercontinuum harmonics, a 26 attosecond pulse can be generated.

Authors:
;  [1];  [2]
  1. University of Guilan, Department of Faculty of Science (Iran, Islamic Republic of)
  2. Shahid Beheshti University, Laser and Plasma Research Institute (Iran, Islamic Republic of)
Publication Date:
OSTI Identifier:
22617056
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 124; Journal Issue: 3; Other Information: Copyright (c) 2017 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; AMPLIFIERS; ELECTRONS; EMISSION; GOLD; HARMONIC GENERATION; HARMONICS; HELIUM IONS; ILLUMINANCE; LASER RADIATION; NANOSTRUCTURES; PULSES; SCHROEDINGER EQUATION; SPECTRA; TIME DEPENDENCE; WAVE FUNCTIONS; WAVELENGTHS

Citation Formats

Hosseinzadeh, F., Batebi, S., E-mail: s-batebi@guilan.ac.ir, and Soofi, M. Q.. Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures. United States: N. p., 2017. Web. doi:10.1134/S1063776117020121.
Hosseinzadeh, F., Batebi, S., E-mail: s-batebi@guilan.ac.ir, & Soofi, M. Q.. Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures. United States. doi:10.1134/S1063776117020121.
Hosseinzadeh, F., Batebi, S., E-mail: s-batebi@guilan.ac.ir, and Soofi, M. Q.. Wed . "Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures". United States. doi:10.1134/S1063776117020121.
@article{osti_22617056,
title = {Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures},
author = {Hosseinzadeh, F. and Batebi, S., E-mail: s-batebi@guilan.ac.ir and Soofi, M. Q.},
abstractNote = {Our work is based on high harmonic generation in a gaseous medium (helium ion), by exploiting gold bowtie nanostructures as laser field amplifiers. As the result of emission of a laser pulse, the wave function of the atom varies with time; so, it is necessary to solve 1D time-dependent Schrödinger equation by means of split operator method. By illumination of a short duration, long wavelength three color laser pulse inside the gap, the enhanced field not only changes with time, but also varies in space. In this work we considered this space inhomogeneity in linear and nonlinear schemes. We show that in nonlinear case, the plateau region is more extended. We also show that in larger gaps, cutoff occurs on higher frequencies. But limitation of electron motion in bowtie nanostructures leads to the choice of an optimum 16 nm gap size in our case. We predict that, by the superposition of supercontinuum harmonics, a 26 attosecond pulse can be generated.},
doi = {10.1134/S1063776117020121},
journal = {Journal of Experimental and Theoretical Physics},
number = 3,
volume = 124,
place = {United States},
year = {Wed Mar 15 00:00:00 EDT 2017},
month = {Wed Mar 15 00:00:00 EDT 2017}
}
  • We describe plasmonic interactions in suspended gold bowtie nanoantenna leading to strong electromagnetic field (E) enhancements. Surface enhanced Raman scattering (SERS) was used to demonstrate the performance of the nanoantenna. In addition to the well known gap size dependence, up to two orders of magnitude additional enhancement is observed with elevated bowties. The overall behavior is described by a SERS enhancement factor exceeding 10^11 along with an anomalously weak power law dependence of E on the gap size in a range from 8 to 50 nm that is attributed to a plasmonic nanocavity effect occurring when the plasmonic interactions entermore » a strongly coupled regime.« less
  • Tuning of the harmonic wavelength by varying the driving radiation wavelength, chirp, and intensity during the interaction of Ti:sapphire laser radiation with preformed laser plasma and solid surfaces was studied. High-order harmonics (HHG) were studied at different spectral, phase, and intensity characteristics of femtosecond radiation. Analysis of the variation of the high-order harmonic distribution in the case of different plumes is presented. We show that the tuning of harmonic wavelength allows achievement of resonance enhancement of single harmonics in the plateau distribution of HHG.
  • We present analytical and numerical calculations of the power and angular distributions of high-order harmonics generated by limited laser beams in extended media with a dispersion weak when compared with the geometric dispersion. When the thickness of the harmonic-generating layer is large, the spectrum of high-order harmonics differs considerably from the spectrum of a single-atom response. In particular, two plateaus may arise in the spectrum of high-order harmonics owing to the off-axially phase-matched generation of certain harmonics (the generation of a part of the angular spectrum of these harmonics is phase-matched). The efficient off-axially phase-matched harmonic generation is provided mainlymore » by amplitude modulation of the high-frequency response of a medium to the pump field in the cross section of the beam, which broadens the radiation pattern of harmonic emission. Off-axially phase-matched harmonic generation in Gaussian beams is possible with any geometric dispersion (with an arbitrarily tight focusing). The results of our calculations agree well with the experimental data on high-order harmonic generation in thick gas layers available from the literature. (nonlinear optical phenomena and devices)« less
  • Using the plasma harmonic method, we show the generation of efficient and intense high-order harmonics from plasma of pencil lead. We demonstrate multimicrojoule energy in each harmonic order for the 11th to the 17th order of a Ti:sapphire laser. By analyzing the target morphology and the plasma composition, we conclude that these intense harmonics are generated from nanoparticles of graphitic carbon.
  • Purpose: Noise characteristics of clinical multidetector CT (MDCT) systems can be quantified by the noise power spectrum (NPS). Although the NPS of CT has been extensively studied in the past few decades, the joint impact of the bowtie filter and object position on the NPS has not been systematically investigated. This work studies the interplay of these two factors on the two dimensional (2D) local NPS of a clinical CT system that uses the filtered backprojection algorithm for image reconstruction. Methods: A generalized NPS model was developed to account for the impact of the bowtie filter and image object locationmore » in the scan field-of-view (SFOV). For a given bowtie filter, image object, and its location in the SFOV, the shape and rotational symmetries of the 2D local NPS were directly computed from the NPS model without going through the image reconstruction process. The obtained NPS was then compared with the measured NPSs from the reconstructed noise-only CT images in both numerical phantom simulation studies and experimental phantom studies using a clinical MDCT scanner. The shape and the associated symmetry of the 2D NPS were classified by borrowing the well-known atomic spectral symbols s, p, and d, which correspond to circular, dumbbell, and cloverleaf symmetries, respectively, of the wave function of electrons in an atom. Finally, simulated bar patterns were embedded into experimentally acquired noise backgrounds to demonstrate the impact of different NPS symmetries on the visual perception of the object. Results: (1) For a central region in a centered cylindrical object, an s-wave symmetry was always present in the NPS, no matter whether the bowtie filter was present or not. In contrast, for a peripheral region in a centered object, the symmetry of its NPS was highly dependent on the bowtie filter, and both p-wave symmetry and d-wave symmetry were observed in the NPS. (2) For a centered region-ofinterest (ROI) in an off-centered object, the symmetry of its NPS was found to be different from that of a peripheral ROI in the centered object, even when the physical positions of the two ROIs relative to the isocenter were the same. (3) The potential clinical impact of the highly anisotropic NPS, caused by the interplay of the bowtie filter and position of the image object, was highlighted in images of specific bar patterns oriented at different angles. The visual perception of the bar patterns was found to be strongly dependent on their orientation. Conclusions: The NPS of CT depends strongly on the bowtie filter and object position. Even if the location of the ROI with respect to the isocenter is fixed, there can be different symmetries in the NPS, which depend on the object position and the size of the bowtie filter. For an isolated off-centered object, the NPS of its CT images cannot be represented by the NPS measured from a centered object.« less