Ultrashort bunches of electrons, emitted from solid surfaces through excitation by ultrashort laser pulses, are an essential ingredient in advanced X-ray sources, and ultrafast electron diffraction and spectroscopy. Multiphoton photoemission using a noble metal as the photocathode material is typically used but more brightness is desired. Artificially structured metal photocathodes have been shown to enhance optical absorption via surface plasmon resonance but such an approach severely reduces the damage threshold in addition to requiring state-of-the-art facilities for photocathode fabrication. Here, we report ultrafast photoelectron emission from sidewalls of aligned single-wall carbon nanotubes. We utilized strong exciton resonances inherent in this prototypical one-dimensional material, and its excellent thermal conductivity and mechanical rigidity leading to a high damage threshold. We obtained unambiguous evidence for resonance-enhanced multiphoton photoemission processes with definite power-law behaviors. In addition, we observed strong polarization dependence and ultrashort photoelectron response time, both of which can be quantitatively explained by our model. These results firmly establish aligned single-wall carbon nanotube films as novel and promising ultrafast photocathode material.

The 25 percent streamflow duration and corresponding depth were selected to represent ordinary high water. Statistical relations of 25 percent flow duration depth to eight basin parameters were analyzed using a stepwise linear regression procedure. A procedure for estimating "ordinary high water" depth was derived using one independent variable drainage area size. Two equations were derived; the standard error of estimate of the equation for hydrologic area 1, the Appalachian Plateaus, is 26 percent and for area 2, the Coastal Plains province, is 39 percent. The equations apply where the stream channels or streamflow is not significantly altered by man's activities.

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