Multifrequency Bessel beams with adjustable group velocity and longitudinal acceleration in free space

Abstract

The group velocity of an optical beam in free space is usually considered to be equal to the speed of light in vacuum. However, it has been recently realized that, by structuring the beam's angular and temporal spectra, one can achieve well pronounced and controlled subluminal and superluminal propagation. In this work, we consider multifrequency Bessel beams that are known to propagate without divergence and show a variety of possibilities to adjust the group velocity of the beam by means of designed angular dispersion. We present several examples of multifrequency Bessel beams with negative and arbitrary positive group velocities, as well as longitudinally accelerating beams and beams with periodically oscillating local group velocities. The results of these studies can be of interest to scientists working in the fields of optical beam engineering, light amplitude and intensity interferometry, ultrafast optics, and optical tweezers.

Continuous wave Bessel beams with a strong longitudinal acceleration in free space

“…Measured group velocity of the longitudinally accelerating Bessel beam (see the blue dots and the estimated error bars).The blue line shows the theoretically predicted group velocity of the beam. The curve corresponds to the theoretical curve shown in Fig.6of Ref [21]. for the current parameter values.…”

“…Recently, a systematic theoretical description of structured pulsed and cw laser beams with varying group velocities in free space has been presented [21]. There it was shown that, for cw beams, the velocity of the intensity peaks can fluctuate or change deterministically both in space and time.…”

“…Being transmitted by the axicon, the collimated component (of frequency ω 1 ) forms a Bessel beam with a constant angular spectrum, while the focused component (of frequency ω 2 ) forms a beam with a local (on-axis) angular spectrum that depends on the coordinate z. As a result, the group velocity of the combined Bessel beam becomes a function of z given by [21]…”