Strong Field Laser Physics
ULTRA-Strong Light Fields:
- In ultrastrong light fields, our common understanding of light - matter interactions begins to fail. The speed of the photoelectron becomes relativistic and the magnetic field of light affects the way light interacts with matter. Our recent research results have characterized this progression from the strong- to ultrastrong-field and shown this can have a significant effect on strong field "rescattering physics" that is responsible for high harmonic generation and multielectron ionization for atoms in strong laser fields.
Instrumentation for the Ultra-Strong Field:
- Ultrahigh intensities mean relativistic interactions. Where traditional laser-matter interactions result in photons and ionization products with eV to 1 keV of energy, the energy scale of ultrastrong fields is an MeV. Such energetic particles require new detection methods closer to nuclear instrumentation. High energy particles transmit right through normal micro-channel plates and time of flight is very limited since all velocities are near the speed of light. The figure above (a) represents the type of chamber currently used to detect photoelectrons for ultrahigh field ionization with high contrast, 40 fs pulses (b,c). Fast scintillation materials and photomultiplier tubes are used as detectors and magnetic field deflection and 150 picosecond timing electronics are used to help analyze the electron energies.
MeV Photoelectrons from Ultrastrong Fields:
- Results from recent photoelectron measurements from ultrastong field interactions with atoms are shown in the above photoelectron spectrum for the ionization of xenon at 1019 W/cm2. The photoelectrons have the highest energy observed from the photoionization of a single atom by optical frequency photons. The angular distibutions of the photoionization (shown just above the spectrum as inserts) have also been measured and are currently being analyzed to provide insight into the fundamentals of the ionization and propagation of the photoelectrons. In any sense of the definition this interaction is highly nonperturbatuve with the light-atom interaction resulting in the absorption of nearly one-million photons during ionization.