Photoelectron spectroscopic determination of the energy bandwidths of high-order harmonics (7th-55th) produced by an ultrafast laser in neon - art. no. 023812

The energy bandwidths of high-order harmonics of a Ti:sapphire ultrafast la ser are extracted from electron kinetic-energy measurements of the photoion ization of gas-phase atoms and molecules. High-order harmonics of the 70 fs , 800 nm laser are produced by focusing approximate to 2.5 mi pulses into a jet of neon gas and are frequency-separated by a grazing-incidence grating . Photoelectrons resulting from the ionization of gaseous samples are energ y-analyzed with a magnetic bottle time-of-flight spectrometer. Energy broad ening of the photoelectron peaks at low kinetic energies are a direct resul t of the energy bandwidths of the harmonics. The energy bandwidths of the h armonics are found to increase from 0.11(+/- 0.03) eV (7th harmonic) to 0.3 7(+/- 0.03) eV (45th harmonic) in a gradual manner. The higher-order harmon ics (47th-55th) appear to reach a plateau at a value of approximate to 0.43 eV. Though a full theoretical treatment of bandwidths of the harmonics for the 70 fs driving pulse regime does not exist, the theories developed for shorter pulses (less than or equal to 30 fs) can give insight into the obse rved results.