Collimated hot electron jets generated from subwavelength grating targets irradiated by intense short-pulse laser

Hot electron emission from subwavelength grating targets irradiated by a 60 fs short-pulse laser was investigated at moderate intensities in excess of 1015 W/cm2. Collimated hot electron jets with a divergence angle as small as 5° were observed at the specular reflection direction when the laser beam was incident at the resonance angle for surface plasmon excitation. When the incident angle, which departs from the resonant angle, is increased, the collimated hot electron jet remains near the specular reflection direction, but its intensity attenuates gradually. At the same time, the number of the hot electrons with very large spreading angle emitting along the target normal direction increases with the incident angle.