Plasma: The Key for Unlocking Compact Multi-Petawatt Lasers?
16 Nov 2020
- Helen Towrie





These frames show the evolution of the scaled duration (Gamma*tau) of the growing short pulse versus its amplitude a1. The short pulse is being amplified, so all curves evolve from low a1 to high a1. The frames (a) and (b) deal with Raman amplification while the frames (c) and (d) deal with Brillouin amplification, a related process with a somewhat different scaling. The dashed line in each frame corresponds to the "rule" we discovered for the amplification process. In the frames (a) and (c), we studied amplification for various regimes of pulse intensities. These frames show that the rule always applies, regardless of the intensities you are using. In the frames (b) and (d), we varied the initial duration of the short pulse, keeping the initial amplitude fixed. This shows that the short pulse will first go back to the dashed line (the "rule"), and only then amplify, sticking close to the rule all the while.


​Published today in Scientific Reports, a team led by Raoul Trines at the Central Laser Facility (CLF), IST Lisbon, Stanford University and St Andrews University, have proposed a novel method that could finally open the door for to efficient Raman or Brillouin amplification, a process that could allow us to achieve multi-petawatt powers in compact laser systems.

Raman amplification is a method to transfer energy from a long pulse with moderate intensity to a much shorter pulse, giving the short pulse a very high intensity in the process. This is usually done using optical fibres, but the high intensity of the short pulse could end up damaging the fibre. Thus, the team aimed to study Raman amplification in plasma.

“You cannot burn a plasma, since effectively it is already burnt," explained Dr Raoul Trines. “This way, we hope to achieve final intensities and powers that rival those of high-power solid-state laser systems, in a much more compact setup."

Achieving such powerful laser acceleration using plasma could allow us to build cheaper, more compact, yet more powerful lasers. One can compare this to the development of plasma-based particle accelerators that could achieve the same outcomes as conventional particle accelerators, but using much more compact experimental setups.

Raman amplification has shown great promise in theory and in computer simulations, but experimental results to date have not yet delivered the predicted levels of amplification.

“We have now unearthed a likely cause for this: the properties of the short pulse before amplification. We made three new discoveries," said Dr Trines.

The first of these discoveries was, during amplification of the short pulse, this pulse follows a strict rule: the product (coupling coefficient)*(pulse duration)*(pulse amplitude) remains approximately 3.4, never moving away from this value.

Second, if you start with a short pulse that does not obey this rule, then the pulse will first change its duration until it does obey the rule, and only then amplify.

Third, in nearly all existing experiments, the initial short pulse is so far away from the optimal shape, and the interaction distance so short, that the interaction is already over before the short pulse has the chance to fully reshape itself, i.e. before true amplification can even start.

Dr Trines and his team expect that future experiments applying these proposed methods will show much better amplification than past experiments.

​Read the paper here.


Contact: Gianchandani, Shikha (STFC,RAL,ISIS)