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Powerful terahertz emission from laser wake fields excited in inhomogeneous plasmas
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10.1063/1.2136107
/content/aip/journal/pop/12/12/10.1063/1.2136107
http://aip.metastore.ingenta.com/content/aip/journal/pop/12/12/10.1063/1.2136107
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(Color online). Schematic of electromagnetic emission from a wake field generated by a laser pulse incident obliquely to the plasma density gradient.

Image of FIG. 2.
FIG. 2.

(Color online). Spatial-temporal plots of the (a) longitudinal electric field , (b) transverse electric field , and (c) magnetic field in the laboratory frame obtained from 1D PIC simulation. The incident pulse has the parameters , , and . The trapezoid plasma profile takes the parameters and . It rises linearly from 0 to between and , then remains homogeneous at up to , and finally declines linearly to 0 again at . The laser pulse runs along at the lower edge of the structure [indicated by dashed black lines in (a) and (b)] having the temporal width of nearly one plasma oscillation and that it is not visible because of polarization. The white solid line in (a) shows with and . The black lines in (b) represent some constant phases for the wake emission (EM) and wake field (ES). The white solid line in (c) shows the vacuum-plasma boundary. The fields are normalized by and .

Image of FIG. 3.
FIG. 3.

(Color online). (a) Emission spectra based on Eq. (9) as a function of the incident angles of the laser pulse for a pulse duration and a density scale length of . (b) Emission spectra as a function of the plasma density scale length for the incident angle of 15° and pulse duration . (c) Emission spectra as a function of the pulse duration at the incident angle of 15° and plasma density scale length . The incident pulse has a sine-square profile.

Image of FIG. 4.
FIG. 4.

(Color online). The integral given in Eq. (10): (a) in the plane for a laser pulse with duration ; (b) in the plane for the plasma scale length . These are obtained for the linear density profile with at and for a sine-square pulse.

Image of FIG. 5.
FIG. 5.

(Color online). (a) Time dependence of the emission at different incident angles for a sine-square laser pulse with and and the plasma parameters with and . The field is normalized by . (b) Comparison of emission spectra between the model calculation and PIC simulations. The simulation results have been multiplied by the same numerical factor. (c) Emission spectra from PIC simulations for different laser intensities. The spectra have been divided by and the spectrum for has also been multiplied by an additional factor of 0.5.

Image of FIG. 6.
FIG. 6.

(Color online). The emission pulse profiles [(a), (b), and (c)] and corresponding spectra (d) obtained from 1D PIC simulations show the tunability by the pulse duration and plasma density. The plasma density has a linear profile that increases from 0 to in a length of . The laser pulse has a sine-square profile with a peak amplitude and an incident angle 15°. Other parameters are (a) and ; (b) and ; (c) and .

Image of FIG. 7.
FIG. 7.

Emission from a tailored density profile. (a) The initial density profile with and ; (b) the emitted pulse profile; (c) the spectrum of the emitted pulse, illustrating that the emission spectrum is tailored within and . The incident laser pulse has a sine-square profile with parameters , , and .

Image of FIG. 8.
FIG. 8.

(Color online). Emitted pulse profiles (a) and corresponding spectra (b) with different plasma scale lengths ( and ). The incident laser pulse has a sine-square profile with parameters , , and .

Image of FIG. 9.
FIG. 9.

(Color online). Emission from an overdense plasma surface. (a) The emitted pulse profiles for different durations ( and ) of the incident laser pulse. (b) The spectra of the produced emission. The incident laser pulse has parameters and . The plasma density increases linearly from 0 to in a distance of .

Image of FIG. 10.
FIG. 10.

The angular distributions of the emission spectra obtained with Eqs. (9) and (13) based on the model calculation for a laser pulse with a Gaussian distribution transversely and a sine-square profile longitudinally for a duration and arbitrary laser amplitudes. The plasma has a linear density profile with at . Other parameters for the laser pulse are (a) and ; (b) and ; (c) and ; (d) and .

Image of FIG. 11.
FIG. 11.

(Color online). Snapshots of the magnetic component of the wake field emission found from 2D PIC simulation at . The laser pulse is incident from the left boundary of the simulation box. It has parameters , , and focused pulse radius (a) or (b). The plasma density increases linearly from 0 at to at marked by the dashed lines. The black solid lines roughly illustrate the emission angles.

Image of FIG. 12.
FIG. 12.

(Color online). Temporal structure of the emitted pulse from plasma to the left side through the left boundary (a) and its spectrum (b) obtained from 2D PIC simulation. The laser pulse is incident from the left boundary of the simulation box. It has the parameters , , and . The plasma density increases linearly from 0 to in a distance .

Image of FIG. 13.
FIG. 13.

(Color online). Snapshots of the magnetic component of the wake-field emission found from 2D PIC simulation at . The incident pulses have parameters , , incident angle , and pulse radius (a) , (b) , and (c) . The plasma density increases linearly from 0 to in as marked by the white solid lines given in (a) and (b). The black solid line in (c) shows the emission direction and the black dashed line is the normal to the vacuum-plasma interface.

Image of FIG. 14.
FIG. 14.

(Color online). The integral given in Eqs. (14) and (16) for the energy conversion efficiency as a function of the (a) plasma density scale length, (b) the pulse transverse diameter, and (c) the longitudinal pulse duration for incident laser pulses with a Gaussian distribution transversely and a sine-square profile longitudinally.

Image of FIG. 15.
FIG. 15.

(Color online). Snapshots of the wake field at found in 2D PIC simulation. The pulse is incident from the left boundary of the simulation box and it has parameters , , and . The plasma density increases linearly from 0 (at ) to (at ). (a) Electron density; (b) longitudinal electric field; (c) magnetic field in the direction.

Image of FIG. 16.
FIG. 16.

(Color online). (a) Temporal profiles of the emitted pulse through the left boundary of the 2D PIC simulation box. (b) Spectra of the emitted pulse through the left boundary. (c) Temporal profiles of the emitted pulse through the left boundary at transverse coordinates and . The parameters for the laser pulse and the plasma density are the same as in Fig. 15. (d) Temporal profiles of the emitted pulses through the left boundary found in 1D PIC simulations for incident laser pulses with peak amplitudes and 3, which have the same longitudinal density profile as in the 2D case.

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/content/aip/journal/pop/12/12/10.1063/1.2136107
2005-12-02
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Powerful terahertz emission from laser wake fields excited in inhomogeneous plasmas
http://aip.metastore.ingenta.com/content/aip/journal/pop/12/12/10.1063/1.2136107
10.1063/1.2136107
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