Several new phenomena in femtosecond laser filamentation

Beginning with an introduction of the physical model of femtosecond laser filamentation widely accepted today, this paper reviews the latest advances we have achieved in the studies of femtosecond laser filamentation, including an experimental verification of higher-order Kerr effect, investigations of remote lasing generated in air, and development of sptiotemperal focusing technique for remote manipulation of femtosecond laser filament. Our findings point out that although a seemingly complete picture of the fundamental processes in the femtosecond laser filamentation has been established, there are still many challenging problems to be solved. For example, recent experiments show that a negative higher-order Kerr effect cannot be ignored during the filamentation, showing the incompleteness of the current understanding on the femtosecond laser filamentation; the physical mechanism of lasing action in air induced by femtosecond laser filamentation has been still unclear; and new methods for fully manipulating both the profiles of femtosecond laser filaments and the spatiotemporal properties of the light fields inside the filaments have yet to be developed. These facts conclude that this field is still full of opportunities for innovation.