Temporal Coherence and Spatial Coherence

2021 ◽  
pp. 39-45
Author(s):  
M. Françon ◽  
N. Krauzman ◽  
J.P. Mathieu ◽  
M. May
Keyword(s):  
Spatial Coherence ◽  
Temporal Coherence

Determining the global coherence of chorus waves in the magnetosphere

2021 ◽  
Author(s):  
Shuai Zhang ◽  
Jonathan Rae ◽  
Clare Watt ◽  
Alexander Degeling ◽  
Anmin Tian ◽  
...  
Keyword(s):  
Growth Parameters ◽  
Time Lag ◽  
Spatial Coherence ◽  
Temporal Coherence ◽  
Geomagnetic Index ◽  
Outer Radiation Belt ◽  
Chorus Waves ◽  
Van Allen Probes ◽  
Temporal And Spatial ◽  
Chorus Wave

<p>Whistler mode chorus waves play a vital role in the Earth’s outer radiation belt dynamics through the cyclotron resonant pitch angle diffusion.     Recent numerical studies have shown that the temporal and spatial variability of wave growth parameters have universal importance for the diffusion process, which should be much larger than those in the traditional averaged diffusion model.       In the present study, we analyzed both the temporal and spatial coherence of chorus wave in a statistical method using data from the EMFISIS instrument onboard the Van Allen Probes A&B from November 2012 to July 2019. In total, we find 3,875 chorus wave events to calculate the correlation of wave amplitudes between Van Allen Probes A&B.      The results show that both the spatial and temporal correlation of chorus waves decrease significantly with increasing spacecraft separation and time lag, and the spatial and temporal coherence of chorus wave only last ~433 km and ~12 s. We also find that the spatial coherence of chorus waves is higher at L>6, on the dayside, or with a lower geomagnetic index (AL*), while the temporal coherence of chorus waves does not depend on the L-shell, geomagnetic index (AL*) or magnetic local time (MLT). Our results will increase the accuracy of modeling wave-particle interactions due to chorus waves.</p>

High-resolution imaging with the schottky emitter FEG TEM

1993 ◽  
Vol 51 ◽  
pp. 1072-1073
Author(s):  
Max T. Otten
Keyword(s):  
Spatial Coherence ◽  
Temporal Coherence ◽  
Energy Spread ◽  
Total System ◽  
High Resolution Imaging ◽  
A Value ◽  
High Tension ◽  
Two Factors ◽  
Resolution Imaging ◽  
Improved Performance

The Philips CM-series Field Emission TEMs, equipped with the Schottky field emitter and operating at 200 kV (CM20 FEG and the newer CM200 FEG) and 300 kV (CM30 FEG) have a dramatically improved performance in HRTEM imaging relative to their LaB6 equivalents (Table 1). The spatial and temporal coherence of these microscopes far exceeds that of similar microscopes equipped with LaB6 filaments. As a result, the information in the HRTEM images proceeds well beyond the point resolution (the information limit for the 200 kV microscopes typically lies around 0.6× their point resolution) (Fig. 1).The information limit is determined by brightness (controlling the illumination semi-angle α and thus the spatial coherence) and the energy spread (controlling the temporal coherence). These two factors are inversely related — if one goes up, the other goes down. The energy spread under HRTEM conditions is ∼0.8 eV, a value that is not inherent to the Schottky emitter but is due to the total system including the emitter and high-tension tank and accelerator.

scholarly journals Spatial coherence of room-temperature monolayer WSe2 exciton-polaritons in a trap

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hangyong Shan ◽  
Lukas Lackner ◽  
Bo Han ◽  
Evgeny Sedov ◽  
Christoph Rupprecht ◽  
...  
Keyword(s):  
Room Temperature ◽  
Zeeman Effect ◽  
Spatial Coherence ◽  
Temporal Coherence ◽  
Light Sources ◽  
Strong Light ◽  
Matter Coupling ◽  
Exciton Polaritons ◽  
System Ground State ◽  
Fundamental Phenomenon

AbstractThe emergence of spatial and temporal coherence of light emitted from solid-state systems is a fundamental phenomenon intrinsically aligned with the control of light-matter coupling. It is canonical for laser oscillation, emerges in the superradiance of collective emitters, and has been investigated in bosonic condensates of thermalized light, as well as exciton-polaritons. Our room temperature experiments show the strong light-matter coupling between microcavity photons and excitons in atomically thin WSe2. We evidence the density-dependent expansion of spatial and temporal coherence of the emitted light from the spatially confined system ground-state, which is accompanied by a threshold-like response of the emitted light intensity. Additionally, valley-physics is manifested in the presence of an external magnetic field, which allows us to manipulate K and K’ polaritons via the valley-Zeeman-effect. Our findings validate the potential of atomically thin crystals as versatile components of coherent light-sources, and in valleytronic applications at room temperature.

Using convergence and spread-of-focus parameters to model spatial and temporal coherence in HRTEM image simulations

1993 ◽  
Vol 51 ◽  
pp. 974-975
Author(s):  
Jan-Olle Malm ◽  
Michael A. O’Keefe
Keyword(s):  
Diffraction Pattern ◽  
Spatial Coherence ◽  
Incident Beam ◽  
Temporal Coherence ◽  
Spot Size ◽  
Real Space ◽  
Partial Coherence ◽  
Hrtem Image ◽  
Degree Of Convergence ◽  
Image Simulations

In all HRTEM images, the incident electron beam suffers from the effects of limited spatial and temporal coherence. These effects produce a smearing of the image, and provide the ultimate limits as to how high a spatial frequency can be transferred to the image (i.e. resolution). The effect of partial temporal coherence is manifested as a spread of focus, and that of partial spatial coherence as incident beam convergence. The effects of partial coherence can be included in HRTEM image simulations by summing images in real space, or by applying an appropriate transmission cross-coefficient (TCC) when computing the image intensity spectrum in reciprocal space. Figure 1 shows a method of including the effects of incident beam convergence by real-space summation. The degree of convergence is estimated by measuring the spot size in the experimental diffraction pattern (a). Each spot in the diffraction pattern is sub-sampled (b), and a series of images is computed at incident beam angles appropriately sampling the convergence cone.

scholarly journals ANALYSIS OF A TWO-CRYSTAL DELAY LINE FOR FEMTOSECOND PULSES OF THE X-RAY FREE ELECTRON LASER

2018 ◽  
pp. 36-46
Author(s):  
V. A. Bushuev ◽  
I. A. Petrov
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Spatial Coherence ◽  
Temporal Coherence ◽  
Diffraction Reflection ◽  
Probe Type ◽  
Statistical Optics ◽  
X Ray ◽  
Pump And Probe ◽  
Dynamic Diffraction

Using the methods of statistical optics the formation of delayed X-ray pulses in the diffraction reflection of an incident pulse with an arbitrary degree of temporal coherence from a system of parallel crystals with different lattice periods is considered. The results are of interest for constructing delay lines in experiments with a time resolution of the pump-and-probe type and realizing of the self-seeding mode to increase the degree of temporal coherence of the X-ray free-electron laser radiation. A rigorous theory of dynamic diffraction in Bragg geometry is applied to the diffraction reflection of short X-ray pulses from a system of two parallel crystals with arbitrary thicknesses, and also, for a system of two pairs of parallel crystals. The dependence of the delay time and the intensity of the delayed pulses on the thickness of the crystals and the distances between them are analyzed. Since the pulses from the X-ray free electron laser have high spatial coherence, i.e. a small angular divergence, but very poor temporal coherence, special attention is paid to the effect of the degree of temporal coherence on the width of the energy spectrum of the incident pulses and on the influence of this width on the intensity of the delayed pulses.

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