X-wave bullets with negative group velocity in vacuum.
Propagation-invariant, X waves with negative group velocity are reported. Beam aperturing allows for a comprehensive analysis concerning the causality of the optical signal and forerunner formation.
Zapata-Rodríguez
Carlos J
CJ
Departamento de Optica, Universidad de Valencia, Burjassot, Spain. carlos.zapata@uv.es
Porras
Miguel A
MA