Chirp waveform control to produce broad harmonic plateau and single attosecond pulse

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Hang Liu ◽  
Cui-Yan Xu ◽  
Xiao-Dan Jing ◽  
Yan Qiao ◽  
Li-Qiang Feng
Keyword(s):  
Instantaneous Frequency ◽  
Free Electron ◽  
Fourier Transformation ◽  
Attosecond Pulse ◽  
The Other ◽  
Laser Parameters ◽  
Waveform Control ◽  
Chirped Pulses ◽  
Attosecond Pulses

Abstract Waveform control of three kinds of chirped pulses (i.e. βt, βt 2 and βt 3) to produce harmonic spectra and attosecond pulses has been investigated. It is found that by properly choosing the chirps, the chirp delays and the other laser parameters, not only the instantaneous frequency of some specific half profiles can be decreased, but also its intensity can be increased. As a result, the free electron can receive more energy when it accelerates in these regions, thus leading to the extension of the harmonic cutoff and harmonic plateau. Finally, through the Fourier transformation of the harmonic spectra and by superposing some harmonics, three single attosecond pulses with the durations of 30 as, 33 as and 39 as can be obtained.

Initial state effect on waveform control of high-order harmonic spectrum and attosecond pulse generation

2021 ◽  
pp. 2150366
Author(s):  
Hang Liu ◽  
Xiaodan Jing ◽  
Yan Qiao ◽  
John McCain ◽  
Liqiang Feng
Keyword(s):  
Harmonic Spectrum ◽  
Pulse Generation ◽  
Attosecond Pulse ◽  
High Order ◽  
High Order Harmonic Generation ◽  
Initial State ◽  
High Order Harmonic ◽  
Waveform Control ◽  
Attosecond Pulses ◽  
Attosecond Pulse Generation

In this paper, the waveform control of high-order harmonic generation and attosecond pulse generation from a different initial state of He atom has been investigated. The results show that (i) by properly controlling the carrier-envelope phases, the time delays and the laser intensities of a 3-color laser pulse, the best waveforms for the harmonic cut-off extension can be found. Although the harmonic cut-offs from the ground initial state and the superposition initial state are almost the same, the harmonic intensities from the superposition initial state are 4 to 5 orders of magnitudes higher than those from the ground initial state. (ii) With the introduction of the inhomogeneous effect, the harmonic cut-offs can be further extended. However, the harmonic intensities from the superposition initial state are remarkably decreased compared with those from the homogeneous pulses, which is unbeneficial to generate the intense attosecond pulses. (iii) When the ground state is chosen to be the initial and with the assistance of the 4th UV pulse, not only the larger harmonic cut-offs can be obtained, but also the stronger harmonic plateaus can be found, which is favorable for producing the intense attosecond pulses. Thus, at the end of this paper, by superposing the harmonics from the best harmonic spectra, the single attosecond pulses with the duration of 36 as can be obtained.

scholarly journals Normal and Abnormal Human Face Detection Based on DCT and FFT Techniques - A Proposed Method

2021 ◽  
Author(s):  
Samir Bandyopadhyay ◽  
Shawni Dutta ◽  
Vishal Goyal ◽  
Payal Bose
Keyword(s):  
Face Detection ◽  
Fourier Transformation ◽  
Input Image ◽  
The Other ◽  
Fast Fourier Transformation ◽  
Length Variation ◽  
Human Face ◽  
Discrete Cosine Transformation ◽  
Cosine Transformation ◽  
Human Face Detection

In today’s world face detection is the most important task. Due to the chromosomes disorder sometimes a human face suffers from different abnormalities. For example, one eye is bigger than the other, cliff face, different chin-length, variation of nose length, length or width of lips are different, etc. For computer vision currently this is a challenging task to detect normal and abnormal face and facial parts from an input image. In this research paper a method is proposed that can detect normal or abnormal faces from a frontal input image. This method used Fast Fourier Transformation (FFT) and Discrete Cosine Transformation of frequency domain and spatial domain analysis to detect those faces.

Darstellung und Kristallstruktur von K2Sb4S7 · H2O / Preparation and Crystal Structure of K2Sb4S7 · H2O

1979 ◽  
Vol 34 (3) ◽  
pp. 383-385 ◽  
Author(s):  
Brigitte Eisenmann ◽  
Herbert Schäfer
Keyword(s):  
Crystal Structure ◽  
Free Electron ◽  
Electron Pair ◽  
Three Dimensional ◽  
The Other ◽  
Water Molecules ◽  
Triclinic System ◽  
Dimensional Network ◽  
Free Electron Pair

Abstract K2Sb4S7 · H2O crystallizes in the triclinic system with a = 1171.4(5) pm, b = 952.0(5) pm, c = 715.6(5) pm and α = 99.36(5)°, β = 86.80(5)°, γ= 103.48(5)°. One half of the Sb atoms has three sulfur neighbours forming with the free electron pair a ψ-ShS3 tetrahedron, while the other half is coordinated by four S atoms to build a ψ-trigonal SbS4 bipyramid. These polyhedra are connected by common edges and corners to a three-dimensional network with two types of channels, in which either K+ ions only or K+ ions and water molecules are located.

Attosecond XUV sources generation from polarized gating two-color chirped pulse

2015 ◽  
Vol 29 (21) ◽  
pp. 1550111 ◽  
Author(s):  
Liqiang Feng ◽  
Hang Liu ◽  
Tianshu Chu
Keyword(s):  
High Order ◽  
Promising Method ◽  
Polarization Angle ◽  
Single Quantum ◽  
Experimental Realization ◽  
Chirped Pulse ◽  
Laser Parameters ◽  
High Order Harmonic ◽  
Attosecond Pulses ◽  
Cycle Pulse

A promising method to generate the attosecond XUV sources from the high-order harmonic has been theoretically presented by controlling the polarized gating two-color chirped pulse. The results show that with the introduction of the chirps, the harmonic has been remarkably extended. Moreover, the harmonic interferences are very sensitive to the polarization angle between the two lasers. Particularly, when the polarization angle is equal to [Formula: see text], the supercontinuum with a single quantum path contribution is achieved, and a series of isolated attosecond pulses with the duration of 33 as are directly obtained. Further, by testing the influences of other laser parameters on the supercontinuum, we found that this polarized two-color chirped scheme can also be achieved in the multi-cycle pulse region, which is much better for experimental realization.

Linienprofilanalyse von Röntgen-Weitwinkelreflexen mittels Fourier-Transformation zur Bestimmung von Mikrospannungen und parakristallinen Störungen / Analysis of X-Ray Line Profiles for Microstrains and Paracrystalline Distortions by Fourier Transformation

1974 ◽  
Vol 29 (8) ◽  
pp. 1152-1158 ◽  
Keyword(s):  
Gaussian Distribution ◽  
Fourier Transformation ◽  
The Other ◽  
Line Profiles ◽  
Linear Polyethylene ◽  
X Ray ◽  
Other Hand ◽  
Distortion Analysis ◽  
Diffraction Patterns

Many synthetic and biopolymers are paracrystalline. The same holds for some catalysts, graphites and semiconductors. This can be proved directly by diffraction patterns, the integral widths being proportional to (sin ϑ)2 for the higher orders of reflection of the same net plane. To test this, three orders of reflections must be observable. Warren, on the other hand, has shown that microstrains with a Gaussian distribution can directly be calculated from the line profiles of only two reflections by Fourier-Transformation. His method is expanded here to other types of microstrains and to paracrystalline distortions by carefully taking into account a termination effect. Examples are given for turbostratic graphite, linear polyethylene and annealed polybutene I. They demonstrate how useful this method is for distortion analysis.

A perspective for investigating photo-induced molecular dynamics from within with femtosecond free electron lasers

2017 ◽  
Vol 19 (30) ◽  
pp. 19536-19544 ◽  
Author(s):  
Nora Berrah
Keyword(s):  
Molecular Dynamics ◽  
Pulse Duration ◽  
Free Electron ◽  
Attosecond Pulse ◽  
Femtosecond Pulses ◽  
Free Electron Lasers ◽  
Near Future

Photo-induced molecular dynamics can now be investigated using free electron lasers (FELs) whose attributes are unprecedented brightness, few femtosecond pulses duration and in the near future few hundreds of attosecond pulse duration.

Classical harmonic oscillator approach of a helical-wiggler free-electron laserwith axial guide field

2000 ◽  
Vol 78 (12) ◽  
pp. 1069-1085 ◽  
Author(s):  
M N Rhimi ◽  
R El-Bahi ◽  
A W Cheikhrouhou
Keyword(s):  
Fixed Point ◽  
Free Electron ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Basic Feature ◽  
Operating Conditions ◽  
The Other ◽  
Guide Field ◽  
Constants Of Motion ◽  
Definition Of

Electron beam dynamics in a helical-wiggler free-electron laser (FEL) with a uniform axial guide magnetic field are studied using a three-dimensional Hamiltonian approach. The basic feature of the analysis is the definition of a rotational variable, [Formula: see text], that plays the primordial role in lowering to the half the dimension of the quadratic Hamiltonian as a system of two uncoupled oscillators with definite frequencies and amplitudes. It is through applying this variable in the vicinity of a fixed point that the Heisenberg picture of the dynamics of the particles comes to light, leading thus to the association of the steady-state ideal helical trajectories with arbitrary trajectories. The approach recognized the usual two constants of motion, one being the total energy while the other is the canonical axial angular momentum, Pz'. If the value of the latter is such that a fixed point exists, the Hamiltonian is expanded about the fixed point up to second order. The so-obtained oscillator characteristic frequencies allowed one to study the different modes of propagation and to identify, and then avoid the problematic operating conditions of the FEL concerned. On the other hand, the amplitudes of the oscillations, which do depend on the frequencies, are fortunately found to be constants of motion and then controlled by the boundary conditions (initial conditions). PACS Nos.: 52.40-w, 52.60+h, 42.55.Tb, 52.75Ms

scholarly journals Generation and characterisation of isolated attosecond pulses at 100 kHz repetition rate

2021 ◽  
Author(s):  
Tobias Witting ◽  
Mikhail Osolodkov ◽  
Felix Schell ◽  
Felipe Morales ◽  
Serguei Patchkovskii ◽  
...  
Keyword(s):  
Surface Science ◽  
Repetition Rate ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Attosecond Pulse ◽  
Light Sources ◽  
Pump Probe ◽  
Attosecond Pulses ◽  
Atomic And Molecular Physics ◽  
Pump Probe Experiment

Abstract The generation of coherent light pulses in the extreme ultraviolet (XUV) spectral region with attosecond pulse durations constitutes the foundation of the field of attosecond science [1]. Twenty years after the first demonstration of isolated attosecond pulses [2], they continue to be a unique tool enabling the observation and control of electron dynamics in atoms, molecules and solids [3, 4]. It has long been identified that an increase in the repetition rate of attosecond light sources is necessary for many applications in atomic and molecular physics [5, 6], surface science [7], and imaging [8]. Although high harmonic generation (HHG) at repetition rates exceeding 100 kHz, showing a continuum in the cut-off region of the XUV spectrum was already demonstrated in 2013 [9], the number of photons per pulse was insufficient to perform pulse characterisation via attosecond streaking [10], let alone to perform a pump-probe experiment. Here we report on the generation and full characterisation of XUV attosecond pulses via HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The high number of 106 XUV photons per pulse on target enables attosecond electron streaking experiments through which the XUV pulses are determined to consist of a dominant single attosecond pulse. These results open the door for attosecond pump-probe spectroscopy studies at a repetition rate one or two orders of magnitude above current implementations.

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