Quantum optics with very intense lasers

Abstract

Traditional concerns of Quantum Optics are coherence and saturation in bound-bound atomic transitions. For the first time these concerns are beginning to be appropriate to the bound-free and free-free spectroscopy of photo-electrons. Recent experimental evidence indicates that laser intensities in the rangeI=10¹²–10¹³ Watts/cm² are sufficient to saturate a variety of multiphoton ionization processes and to create coherent above-threshold dressed electronic states. We first discuss the experimental background, and describe the laser parameters and experimental methods that have been used to obtain the data. Then we review a simple quantum optical description of ionization, and a classical theory of photon-electron interactions. Order-of-magnitude estimates of the ponderomotive potential are given and a relativistic critical field strength is derived. The results of a numerical integration of Schrödinger's equation for an electron being ionized are also shown, including the first theoretical evidence for above-threshold photo-electron peak shifts. The very recent development of terawatt Nd lasers is mentioned. Finally, it is suggested that nonlinear optical processes associated with high-intensity ionization should show new and interesting non-perturbative effects.