The temporal contrast of a high-power laser (i.e. the difference in magnitude between the primary main pulse of light and any prepulses or continuous emission from the laser that precedes the main pulse's arrival on target) is a critical parameter. Many experiments and applications are sensitive to this parameter because for a high-power laser even a relatively weak pre-pulse can contain significant energy. If the main pulse is focused to 1020 W/cm2, even a pre-pulse with six orders of magnitude less energy can cause early ionization and distort the target. As a result, several techniques have been developed to reduce the magnitude of pre-pulses and the plateau for high power lasers.
This invention proposes a volumetric transmission grating based on ionization created in a neutral gas by crossing and interfering two short-pulse pump lasers so that their intensity maxima rise above the medium’s ionization threshold. This will create a modulated index of refraction that can diffract a subsequent probe beam like a transmission grating. Crucially for the application of contrast cleaning, the diffracted probe beam travels in a different direction than the incident beam, and the grating turn-on time is extremely fast. When driven by 30 fs pumps, diffraction efficiency rises from unmeasurable to a maximum in less than a picosecond. If the probe beam and the pump pulses are timed appropriately, the formation of the grating can act like an optical switch, changing the direction that a beam propagates in less than a picosecond.
Current stage of technology development: TRL 1-2
LLNL has filed for patent protection on this invention.
U.S. Patent Application No. 2024/0047930 Temporal Contrast Improvement for Short Pulse Lasers Via Ionization Gratings published 2/8/2024
- Enables 6 orders of magnitude higher contrast than current state-of-the-art plasma mirror approaches.
- Believed to be possible to achieve >80% efficiency with <1ps turn on time and >1010 contrast improvement.
- Intense ultrafast lasers for high energy density physics, secondary particle creation and plasma wakefield acceleration.
- Inertial confinement fusion research.
- Ultrafast X-ray radiography in medicine.
- Electron and ion beams for cancer therapy.
