High-order harmonic generation with an annular laser beam.
High-order harmonics have been generated by the use of an annular laser beam. The nonlinearity of harmonic production and the shorter wavelengths involved cause the harmonics to emerge strongly peaked on the laser axis. Thus the harmonics emerge from the focus inside the missing portion of the laser beam. This permits the laser to be blocked by an aperture that passes the harmonics.
J
J
Peatross
J L
JL
Chaloupka
D D
DD
Meyerhofer