Relativistic Broadband Spatio-Temporal Light Springs – A New Tool for Exploring Laser Plasma Interactions*

Laser-plasma interactions driven by relativistic beams carrying orbital angular momentum (OAM) have become accessible with recent advances in optics manufacturing. However, transferring OAM from a monochromatic beam to plasma remains challenging as OAM is nominally encrypted in the laser phase and plays only a small role in ponderomotively driven interactions such as wakefield acceleration. Spatio-temporal structures carrying OAM in both their phase and amplitude can be created from the superposition of 2 or more OAM beams with different wavelengths. Referred to as ‘light springs’, these beams propagate with an intensity profile that is azimuthally dependent allowing for ponderomotive coupling of OAM to plasmas.

 

In this work, we demonstrate a novel and practical approach to both generating and measuring broadband light springs in existing high power laser facilities. These light springs consist of a broad range of colors and OAM states and have unique properties such as programmable transverse spot motion, focal spots that can accelerate and decelerate azimuthally, as well as programmable effective group velocities in plasmas. Results will be compared to simulations and theory followed by a discussion on potential applications of these beams.