Optical wave-packet with nearly-programmable group velocities

Abstract

During the process of Bessel beam generation in free space, spatiotemporal optical wave-packets with tunable group velocities and accelerations can be created by deforming pulse-fronts of injected pulsed beams. So far, only one determined motion form (superluminal or luminal or subluminal for the case of group velocity; and accelerating or uniform-motion or decelerating for the case of acceleration) could be achieved in a single propagation path. Here we show that deformed pulse-fronts with well-designed axisymmetric distributions (unlike conical and spherical pulse-fronts used in previous studies) allow us to obtain nearly-programmable group velocities with several different motion forms in a single propagation path. Our simulation shows that this unusual optical wave-packet can propagate at alternating superluminal and subluminal group velocities along a straight-line trajectory with corresponding instantaneous accelerations that vary periodically between positive (acceleration) and negative (deceleration) values, almost encompassing all motion forms of the group velocity in a single propagation path. Such unusual optical wave-packets with nearly-programmable group velocities may offer new opportunities for optical and physical applications.

Space-time wave packets

“…Recent theoretical work by Li et al [295][296][297] has introduced new ideas exploiting carefully sculpted angular dispersion to produce wave packets that accelerate with arbitrary axial profiles of the group velocity that complement the experimental approach in [45,294].…”

Spectral reorganization of space-time wave packets in presence of normal group-velocity dispersion

“…Space-time wave packets (STWPs) are a class of spatio-temporally structured pulsed optical fields that are propagation-invariant in linear media [1][2][3][4][5][6]. To date, STWPs have been experimentally studied predominantly in free space [7] and non-dispersive dielectrics [8], in which a host of useful characteristics of STWPs have been verified, including: tunable group velocities [4,9,10] and acceleration [11][12][13][14][15][16][17], self-healing [18], and anomalous refraction [19,20]. Moreover, almost arbitrary dispersion profiles can be introduced in free space [21,22], which has enabled the observation of the space-time Talbot effect [23].…”

Reciprocating propagation of laser pulse intensity in free space

“…Currently, the spatiotemporal (ST) coupling is frequently used to modulate the propagation or structure of a pulsed beam, which permits both velocity control (i.e., superluminal or subluminal, and accelerating or decelerating) and direction control (i.e., forward or backward) [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. The first example is the 3-dimensional (3-D) flying focus (FLFO) within the extended Rayleigh length independently demonstrated by Quéré, et al [24,25] (originally named "sliding focus") and Froula, et al [26,27] (originally named "flying focus"), respectively, which can propagate at an arbitrary group velocity in free space including all motion forms of superluminal or subluminal, accelerating or decelerating, and forward or backward propagations.…”

“…The second example is the 2-D optical ST wave-packet demonstrated by Abouraddy, et al [28][29][30][31][32][33][34], which can also propagate at an arbitrary group velocity in free space including all above motion forms. The third example is the 3-D ST Gauss-Bessel pulsed-beam (or 3-D optical wave-packet) created by pre-deforming the pulse-front of the input Gauss pulsed-beam that is for the generation of a Gauss-Bessel pulsedbeam [35,36], similarly whose group velocity is tunable, too. Apart from the above motion forms (i.e., superluminal or subluminal, accelerating or decelerating, and forward or backward propagations), a compound motion with several different motion forms in a single propagation path is also possible [36].…”