Laser beam shaping is an active discipline in optics owing to its importance to both illumination and detection processes. The formation of single or multiples optical vortices in a laser beam has taken on recent interest in areas ranging from electron and atom optics to astronomy. An optical vortex is characterized as a point node of destructive interference around which the phase varies by an integer multiple of 2 times π. Here we describe our efforts to create localized vortex cores using only the interference of several Gaussian profile laser beams, a method that may be particularly suited to the application of vortex modes to intense femtosecond laser pulses.
We have demonstrated electron diffraction from a standing light wave. More recently, we have also demonstrated the onset of Bragg scattering for electrons by a thick standing wave of light. Here, we investigate the use of thick Bragg crystals for the electron analogue of acousto-optical modulators. In atom optics it has been shown both theoretically and experimentally that effects analogous to acousto-optical modulation can be achieved for atoms. Based on this approach we estimate the experimental parameters needed for electrons.
It is perhaps surprising that atomic and electron beams with poorly defined energy can be used for diffraction and interferometry. It may also be surprising that we consider modulation at frequencies much smaller than the frequency width of the electron beam as being useful. This contrasts the usual optical application of AOM's as a frequency shifter. For white light interferometers, the use of such modulation promises a greatly improved signal to noise by providing a beatnote in the interference signal at the modulation frequency.