Plasma optics refers to the use of plasmas to manipulate light in ways that are similar to solid-state optics. The disadvantage of standard solid-state-based optics is that they have a damage threshold that limits the admissible power and energy densities. Plasma has already been broken down and can therefore withstand extremely high light intensities and energy densities.
Plasmas can, then, be used for areas such as the following:
- Amplify light pulses
- Focus light pulses to the diffraction limit
- Diffract light.
Plasmas might present a way forward for creating Exawatt light pulses using very small spatial scales. Light can be amplified in plasma by relying on parametric instabilities that occur when laser light is interacting with preformed plasma. Parametric instabilities such as Raman or Brillouin backscattering are detrimental in inertial confinement fusion but can be beneficial when exploited in a controlled way to create short and intense light pulses. The mechanism relies on the fact that two transverse electromagnetic waves can be coupled in plasma by either Raman backscattering (SRS), an electron plasma wave, or Brillouin backscattering (SBS), an ion-acoustic wave. This three-wave coupling process takes the form of an instability that allows the amplitude of one wave to grow at the expense of the other wave. The plasma wave is necessary to fulfill the fundamental conservation laws of momentum and energy. A long pump pulse of moderate intensity collides with a short seed pulse inside the plasma. The three-wave coupling process then provides an energy transfer from the pump to the seed, thereby increasing the intensity of the latter. In the ideal case, pump-depletion occurs, which means that all the energy of the pump pulse is scattered into the seed pulse. In this scenario, the seed provides the time scale and the pump is the energy reservoir. By properly selecting the parameter space of the operation, competing instabilities such as filamentation can be avoided. This implies that the amplification process can take place over large cross-sectional areas. The next step involves focusing the amplified pulse by using an ellipsoidal plasma mirror. Research in this area generally involves the use of the Brillouin instability in the so-called strong-coupling regime (sc-SBS) because it has several advantages over the Raman instability. The key feature of sc-SBS is that it is a driven mode rather than an Eigenmode of the plasma. In this quasi-mode regime the properties of the electrostatic mode (the plasma response) are determined by the laser pump field. Plasma optics is quite a young field in optics and laser science, but it has huge potential because there is a constant push for ever higher laser intensities and ways to handle and manipulate it. P3, which can use both high-energy laser beams and short-pulse beams, offers a unique way to perform research on plasma optics.
REFERENCES:
- A.A. Andreev et al. Short light pulse amplification and compression by stimulated Brillouin scattering in plasmas in the strong coupling regime, Phys. Plasmas 13, 053110 (2006).
- L. Lancia et al. Experimental evidence of short light pulse amplification using strong-coupling stimulated Brillouin scattering in the pump depletion regime, Phys. Rev. Lett. 104, 025001 (2010).
- S. Weber et al. Amplification of ultrashort laser pulses by Brillouin backscattering in plasmas, Phys. Rev. Lett. 111, 055004 (2013).
- C. Riconda et al. Spectral characteristics of ultra-short laser pulses in plasma amplifiers, Phys. Plasmas 20, 083115 (2013).
- J. Fuchs et al. Plasma devices for focusing extreme light pulses, Eur. Phys. J. ST 223, 1169 (2014).
- G. Lehmann et al. Regions for Brillouin seed pulse growth in relativistic laser-plasma interaction, Phys. Plasmas 19, 093120 (2012).
Stefan WEBER, stefan.weber@eli-beams.eu
