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.
© 2006 Optical Society of America
Original Manuscript: July 27, 2006
Revised Manuscript: September 12, 2006
Manuscript Accepted: September 12, 2006
Published: November 9, 2006
Carlos J. Zapata-Rodríguez and Miguel A. Porras, "X-wave bullets with negative group velocity in vacuum," Opt. Lett. 31, 3532-3534 (2006)