Smoothing scheme for intensity sweep and polarization rotation at a subpicosecond timescale

Muyu Yi; Zheqiang Zhong; Bin Zhang

doi:10.1364/JOSAB.37.000188

Journal of the Optical Society of America B
Vol. 37,
Issue 1,
pp. 188-196
(2020)
•https://doi.org/10.1364/JOSAB.37.000188

Smoothing scheme for intensity sweep and polarization rotation at a subpicosecond timescale

Muyu Yi, Zheqiang Zhong, and Bin Zhang

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Muyu Yi, Zheqiang Zhong, and Bin Zhang, "Smoothing scheme for intensity sweep and polarization rotation at a subpicosecond timescale," J. Opt. Soc. Am. B 37, 188-196 (2020)

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Abstract

A novel scheme for decreasing the scattering levels of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), as well as for improving illumination uniformity of focal spots, is proposed. In this scheme, four beamlets in a laser quad are frequency shifted, spatial phase shaped by conjugate phase plates, and counter-rotating circularly polarized by polarization control plates before being focused by wedged lenses. Consequently, the intensity sweep and the polarization rotation of the focal spot in the timescale of a subpicosecond are achieved, resulting in the reduction of the scattering level of SRS and SBS, and also the improvement of the illumination uniformity when the frequency shift among beamlets is comparable to the parametric backscattering growth rate and the filamentation instability growth rate. The theoretical model of the novel smoothing scheme has been established, and the influences of some key parameters including spatial modulation type, peak-to-mean value of phase distortion, and frequency shift have been discussed. Results show that the uniformity of the focal spot of this novel scheme is improved much faster than that of the conventional temporal smoothing scheme, i.e., smoothing by spectral dispersion. The parametric instabilities are significantly reduced and both phase distortion and modulation depth of the laser quad have a large tolerance, opening a new dimension for controlling the incident light in laser plasma interaction.

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Supplementary Material (4)

Name	Description
Visualization 1	Dynamic diagram of tilted phase.
Visualization 2	Dynamic diagram of cylindrical phase.
Visualization 3	Dynamic diagram of elliptical phase.
Visualization 4	Dynamic diagram of spiral phase.

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Equations (22)

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Wavefront Shaping Element	$Φ (x, y)$	Variation of the Interference Structure	Sweep Characteristics of Speckles
Tilted phase	$Φ (x, y) = l x$ ( $l$ is constant)	Transverse variation	Redistribution in $x$ direction
Cylindrical phase	$Φ (x, y) = e x p (- x^{2} / w^{2})$	Transverse variation	Redistribution in $x$ direction
Elliptical phase	$Φ (x, y) = e x p (- a^{2} x^{2} / w^{2} - b^{2} y^{2} / w^{2})$	Zooming	Redistribution in radial direction
Spiral phase	$Φ x, y = a n g l e y / x$	Rotation	Redistribution in azimuthal direction

Regimes	Conditions of Laser and Plasma	$b$	$R / R_{0}$
Only valid in the linear regime		$\frac{π}{2}$	0.15
SRS is Landau damped due to the high electron temperature, dominant over SBS	$I_{0} = 5 \times 10^{14} W / {c m}^{2}$ ; $τ = 15 p s$ ; $n_{0} = 5 \times 10^{20} {c m}^{- 3}$ ; $T_{e} = 1000 e V$ ; $T_{i} = 50 e V$	$\sqrt{2}$	0.22
A sum of two frequency-shifted linearly polarized beams		1.27	0.33
The electron temperature is lower such that SRS is not Landau damped, dominant over SRS	$I_{0} = 10^{15} W / {c m}^{2}$ ; $τ = 3 p s$ ; $n_{0} = 2 \times 10^{20} {c m}^{- 3}$ ; $T_{e} = 100 e V$ ; $T_{i} = 50 e V$	1.25	0.36

Wavefront Shaping Element	$Φ (x, y)$	Variation of the Interference Structure	Sweep Characteristics of Speckles
Tilted phase	$Φ (x, y) = l x$ ( $l$ is constant)	Transverse variation	Redistribution in $x$ direction
Cylindrical phase	$Φ (x, y) = e x p (- x^{2} / w^{2})$	Transverse variation	Redistribution in $x$ direction
Elliptical phase	$Φ (x, y) = e x p (- a^{2} x^{2} / w^{2} - b^{2} y^{2} / w^{2})$	Zooming	Redistribution in radial direction
Spiral phase	$Φ x, y = a n g l e y / x$	Rotation	Redistribution in azimuthal direction

Regimes	Conditions of Laser and Plasma	$b$	$R / R_{0}$
Only valid in the linear regime		$\frac{π}{2}$	0.15
SRS is Landau damped due to the high electron temperature, dominant over SBS	$I_{0} = 5 \times 10^{14} W / {c m}^{2}$ ; $τ = 15 p s$ ; $n_{0} = 5 \times 10^{20} {c m}^{- 3}$ ; $T_{e} = 1000 e V$ ; $T_{i} = 50 e V$	$\sqrt{2}$	0.22
A sum of two frequency-shifted linearly polarized beams		1.27	0.33
The electron temperature is lower such that SRS is not Landau damped, dominant over SRS	$I_{0} = 10^{15} W / {c m}^{2}$ ; $τ = 3 p s$ ; $n_{0} = 2 \times 10^{20} {c m}^{- 3}$ ; $T_{e} = 100 e V$ ; $T_{i} = 50 e V$	1.25	0.36

Abstract

Supplementary Material (4)

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Figures (9)

Tables (2)

Equations (22)

Journal of the Optical Society of America B