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Self-organized coherent bursts of stimulated Raman scattering and speckle interaction in multi-speckled laser beams
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10.1063/1.4774964
/content/aip/journal/pop/20/1/10.1063/1.4774964
http://aip.metastore.ingenta.com/content/aip/journal/pop/20/1/10.1063/1.4774964

Figures

Image of FIG. 1.
FIG. 1.

Upper: The instantaneous reflectivity for an isolated F/8 speckle at . Lower: The time-integrated hot electron fluxes exiting the simulation boundaries (see the schematic in the middle panel); each color curve shows the flux obtained at the boundaries of corresponding color (the flux of the Maxwellian background is indicated by the gray curve).

Image of FIG. 2.
FIG. 2.

Top: Head-on view of laser speckles in 2D (left) and 3D (right) geometry. In 2D, every hot electron that leaves a large amplitude speckle (shown in blue) and moves to the right encounters the neighboring speckle. In 3D, only a fraction of the hot electrons encounter a given neighboring speckle. As a consequence, inter-speckle coupling via exchange of hot electrons should be weaker in 3D than in 2D. Upper middle: Depiction of a 3D, two-speckle simulation which includes a nonlinear, strong speckle above at peak intensity and a neighboring weak speckle below at . Lower middle: The instantaneous reflectivity from a simulation in which both speckles are polarized along y. Bottom: The field at showing SRS daughter EPW in both speckles that have the same laser polarization.

Image of FIG. 3.
FIG. 3.

Upper frames: Reflectivity (left) and pump field (right) from a multi-speckled simulation in a domain 500 × 80 μm at and ; the black arrow indicates the first SRS burst from strong speckles in the while oval; bursts are indicated by the red arrows. Middle and lower frames: Snap shots of quantity , proportional to the backscatter Poynting flux, showing spatial locations of SRS bursts. Middle left inset: time-averaged (over simulation duration 13.36 ps) electron velocity space distribution measured at the location of the strong speckles (spatially averaged over ), showing a strong trapping tail. Middle right inset: The field containing both laser and the scattered light wavefronts distinguished by their different wavelengths (as labeled). SRS backscatter light wave bowing occurring in multiple speckles with two strong speckles centered around z = 14 and 23 μm. Lower right inset: Time-averaged (over ) SRS spectral power as a function of transverse wavenumber measured at the laser entrance (enhanced online). [URL: http://dx.doi.org/10.1063/1.4774964.1]doi: 10.1063/1.4774964.1.

Image of FIG. 4.
FIG. 4.

Flux of SRS side-loss hot electrons and forward hot electrons (theflux of the Maxwellian background) from the simulation shown in Fig. 3 at average pump intensity (top frame) and (lower frame).

Image of FIG. 5.
FIG. 5.

SRS reflectivity scaling with from 2D single-speckle simulations 19 (indicated by the circles), 2D multi-speckle simulations with pump only at average pump intensity (diamonds), and for seeded SRS at average pump intensity and average seed intensity (triangles). The dashed curves are fits .

Image of FIG. 6.
FIG. 6.

Results from a seeded simulation at (with a linear density gradient in x) at average pump intensity and average seed intensity . Top: The frequency spectrum measured at the laser entrance boundary in which the bandwidth of the seeds is depicted by the red curve. Upper and lower middle: Collective SRS bursts with and the time average reflectivity. Bottom: The time-integrated energy flux of side-loss and forward hot electrons.

Image of FIG. 7.
FIG. 7.

The time-integrated energy flux of side-loss and forward hot electrons for a range of values at 0.23, 0.3 (without seeds or density gradient), 0.36 (without seeds but with density gradient), and 0.51 from a seeded simulation at average seed intensity and with a linear density gradient in x.

Image of FIG. 8.
FIG. 8.

Left frames: The instantaneous reflectivity at (the simulation is indicated by the green diamond in Fig. 5 ) and at and 0.51 (the simulations indicated by the red triangles in Fig. 5 ) showing large bursts of SRS with as manifestation of self-organized, collective SRS resulting from electron trapping enhanced speckle interaction. Right frames: Time-resolved SRS spectrum vs. transverse wavenumber at these values for large SRS bursts (marked with letter “A” in the left frames) indicated by the solid curves as compared to the SRS spectra during times when self-organized coherent SRS events are absent (marked with letter ‘B’ in the left frames) indicated by the dotted curves (the relative amplitude between the solid and dotted curves is arbitrary).

Image of FIG. 9.
FIG. 9.

Results from a crossing-beam simulation with size 500 × 262 μm at in which the pump beam cross the seed beam at an angle (left frame); the average pump intensity is , the average broadband seed intensity is , and the plasma has a linear density gradient along x. Middle and right frames: Coherent bursts with and the time-averaged reflectivity. The SRS Poynting flux for steady, low level scatter is along the seed beam direction, whereas the Poynting flux for strong SRS bursts is along the pump beam path (enhanced online). [URL: http://dx.doi.org/10.1063/1.4774964.2]doi: 10.1063/1.4774964.2.

Image of FIG. 10.
FIG. 10.

Upper left frame: SRS reflectivity vs. laser average intensity scaling for collections of speckles at (density and ) without field (triangles) and with field at (squares). Upper middle frame: SRS reflectivity vs. average seed intensity at (density at the center of the x-domain and ) without field (triangles) and with field at . Upper right frame: SRS reflectivity vs. with field for average seed intensity at (triangles) and (squares). Lower left: The time-integrated energy flux of side-loss and forward hot electrons for at average pump intensity with field ( ). Lower middle and right frames: The time-integrated energy flux of side-loss and forward hot electrons for at average pump intensity and average seed intensity without field and with field ( ). The simulations have size 500 × 80 μm.

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/content/aip/journal/pop/20/1/10.1063/1.4774964
2013-01-09
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Self-organized coherent bursts of stimulated Raman scattering and speckle interaction in multi-speckled laser beams
http://aip.metastore.ingenta.com/content/aip/journal/pop/20/1/10.1063/1.4774964
10.1063/1.4774964
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