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Los Alamos National Laboratory

Los Alamos National Laboratory

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Laser Plasma Interactions

Understanding and controlling laser produced plasmas for fusion and basic science

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Thomson scattering is widely used to measure plasma temperature, density, and flow velocity in laser-produced plasmas at Trident, and is also used to detect plasma waves driven by unstable and nonlinear processes.

A typical configuration uses a low intensity laser beam (2nd, 3rd, or 4th harmonic of 1054-nm) to probe a plasma volume. The Thomson scattered light is collected by a lens and is measured using a spectrometer coupled to a gated or streaked camera. The range of plasma wave numbers probed is determined by the Thomson probe beam wavelength and scattering geometry.

Thomson scattering is routinely used at Trident in various configurations including self-Thomson scattering, imaging Thomson scattering, streaked Thomson scattering, and to obtain “ω-k” plasma wave dispersion.

The Thomson scattered spectrum can be measured with temporal resolution ~ 10 ps, spatial resolution ~ 10-µm, and spectral resolution ~ 0.5 Å.

Backscattered diagnostics

Coupling of the laser beam energy to a given target is important in both fundamental and applied laser-matter interaction experiments.

The intense laser beam can drive parametric instabilities which scatter laser light primarily in the backward direction, resulting in a loss of laser energy in the target. Measurements of the backscattered light include the reflected energy, time-resolved spectra, and time-integrated angular distribution of the light scattered just outside the lens (near backscatter).

Backscattered diagnostics can be deployed both for random phase plate smoothed laser beams, and the near-diffraction-limited single hot spot laser beam. The backscattered light can be measured with temporal resolution ~ 10 ps, and spectral resolution ~ 0.5 Å.

Related images


Streaked Thomson scattering from electron plasma waves in a gas jet laser produced plasma.

Streaked Thomson scattering from electron plasma waves in a gas jet laser produced plasma. The probe laser is a 1-ns pulse, followed by three 100-ps pulses. The time-dependent plasma density can be deduced from the spectral shifts.


Time-resolved backscattered spectra

Time-resolved backscattered spectra from a N2H2 gas jet plasma experiment, shot number 20040. The narrow spectrum near 527-nm is from stimulated Brillouin scattering, and the broad spectrum between 650 – 730 nm is from stimulated Raman scattering.


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