| In the interaction of a short laser pulse with an atom or molecule, the strong field regime is realized when the strength of the laser's electric field is comparable to that of the Coulomb binding field. For several years now, these laser field strengths have been achievable using neodymium-based (1 mum) and titanium:sapphire-based (0.8 mum) laser technologies. This has led to the discovery of surprising phenomena such as above-threshold ionization (ATI) and high-harmonic generation (HHG). HHG has subsequently been used to generate light pulses with durations on the order of tens of attoseconds (1 as = 10-18 s), opening up the exploration of dynamics in atoms and molecules on the time scale of the electronic motion.;Numerous studies have detailed the role of the intensity of the laser field, but the range of laser wavelengths over which the strong field interaction has been explored has been limited by the availability of sources. In addition, this wavelength constraint has imposed a restriction on the type of neutral atoms that have been explored. In order for an atom to experience the peak intensity of the laser pulse, it must not completely ionize during the intensity increase on the pulse's rising edge. In practice, this has restricted laser strong field exploration to atoms with high ionization potentials, specifically the noble gases.;In this dissertation, strong field studies of the weakly bound neutral cesium atom, utilizing a unique, intense, 100 fs, mid-infrared laser (3.6 mum), are presented. Photoelectron energy spectra are shown which exhibit very high order ATI peaks, and electron energies many times the cesium ionization threshold energy. The 31st harmonic of the 3.6 mum light has been observed. In addition, a cross-correlation frequency-resolved optical-gating (XFROG) technique has been used to measure the complete spectral amplitude and phase of harmonics 5 through 13, as well as their relative phase. The harmonics are found to exhibit negative dispersion, where the higher harmonic orders lead the lower orders in time. The complete temporal reconstruction including harmonics 7-13 consists of a train of pulses with a temporal envelope having a full-width at half-maximum of 40 fs and individual pulse durations ∼2 fs, which is 1/6 of the driving laser period. |
