Modified Plasma Mirrors to Maximize Efficiency of High Harmonic Generation in Solids

Princeton University, Princeton NJ

Investigators

Abstract

Plasma mirrors -- microscopically small, momentary light reflectors formed by high-power laser beams irradiating and ionizing solid surfaces -- are powerful photonic devices for manipulating light that is too intense to be handled by conventional optics. Not only can plasma mirrors redirect and focus high-power light, they can also serve as ultrafast nonlinear filters suppressing unwanted noise in pulsed laser beams, and as generators of frequencies from terahertz to x-rays for applications that are beyond the reach of current light sources. Using micro- and nano-structures as well as ultralight materials as a base for transient plasma mirrors can potentially make them more efficient, enhance their light modification properties, and add new functionalities to advance x-ray biomedical imaging and ultrafast metrology. This project investigates how novel material structures can affect intense laser-plasma interactions and the efficiency of frequency up-conversion by plasma mirrors to produce higher energies of the radiation. The efficiency of high-order-harmonic emission from overdense relativistic laser-produced plasmas scales with the ratio of laser field strength to plasma density as a result of the balance of forces that produces emitting relativistic electrons. Condensed-phase materials that are fully ionized by ultrahigh-contrast laser beams tend to be too dense for all but the most powerful laser systems to reach the condition of high efficiency. One way of reducing the effective density of the plasma, while keeping a steep density gradient, is to make plasma thinner by using a free-standing nanometer-scale foil, such as multi-layer graphene, as a base material; another way is to use an ultralight nanoporous material. The aim of this project is to study the behavior of femtosecond light pulses at multi-terawatt peak powers focused down to a few micrometers in the interaction with dense relativistic laser-produced plasmas. These plasmas will be created in materials with micro- and nanoscale structure, such as v-grooves, free-standing nanometer foils, and aerogels. Experiments and numerical simulations will be developed for a variety of material structures. This research will achieve fundamental understanding of frequency up-conversion in plasma mirrors and the potential of structured and ultralight materials to maximize its efficiency. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.