Absolute-phase phenomena in photoionization with few-cycle laser pulses

Currently, the shortest laser pulses(1) that can be generated in the visibl e spectrum consist of fewer than two optical cycles (measured at the full-w idth at half-maximum of the pulse's envelope). The time variation of the el ectric field in such a pulse depends on the phase of the carrier frequency with respect to the envelope- the absolute phase. Because intense laser-mat ter interactions generally depend on the electric field of the pulse, the a bsolute phase is important for a number of nonlinear processes(2-8). But cl ear evidence of absolute-phase effects has yet to be detected experimentall y, largely because of the difficulty of stabilizing the absolute phase in p owerful laser pulses. Here we use a technique that does not require phase s tabilization to demonstrate experimentally the influence of the absolute ph ase of a short laser pulse on the emission of photoelectrons. Atoms are ion ized by a short laser pulse, and the photoelectrons are recorded with two o pposing detectors in a plane perpendicular to the laser beam. We detect an anticorrelation in the shot-to-shot analysis of the electron yield.