Control of laser high-harmonic generation with counterpropagating light - art. no. 133902

Relatively weak counterpropagating light is shown to disrupt the emission o f laser high-harmonic generation. Harmonic orders ranging from the teens to the low thirties produced by a 30-femtosecond pulse in a narrow argon jet are "shut down" with a contrast as high as 2 orders of magnitude by a chirp ed 1-picosecond counterpropagating laser pulse (60 times less intense). Alt ernatively, under poor phase-matching conditions, the counterpropagating li ght boosts harmonic production by similar contrast through quasiphase match ing where out-of-phase emission is suppressed.