Arrays of frozen waves: Some theory and experiments

A priori, all beams or pulses are subject to progressive spatial spreading along their propagation even in homogeneous media: Such an effect (diffraction) is always a limitation when the beam is desired to maintain its transverse shape. However, there are wave groups that can withstand diffraction; they are called Localized Waves or Nondiffracting Waves and, because of this property, their applications are being intensively explored. Special Localized Waves are the so-called “Frozen Waves” (FWs), whose longitudinal intensity pattern can be modeled at will within a prefixed space interval. The present work refers to arrays of FWs, namely, to sets of FWs spaced apart transversely and parallel to each other. Our main aim, in fact – after a brief theoretical introduction – is generating arrays of FWs in free space by holographic methods, that is to say, by computer generated holograms optically reproduced by a spatial light modulator. Our present results confirm once more the so-called “Frozen Wave method”, developed years ago. Arrays of optical beams of this type can possess applications in optical tweezers, medicine, atom guiding, remote sensing, and so on.