Wave function of a photoelectron and its collapse in the photoemission process

Based on the first-order perturbation theory, we show that the wave function of a photoelectron is a wave packet with the same width as the incident light pulse. Photoelectron detection measurements revealed that the widths of signal pulses were much shorter than the light pulse and independent of the origin (photoemission or other noises), which is an experimental observation of the wave function collapse. Signal pulses of photoelectrons were distributed along the time axis within the same width as the light pulse, consistent with the interpretation of a wave function as a probability distribution.