The first, second, third, and fourth harmonics of Smith-Purcell radiation in a broadband ranging from 330 nm in the ultraviolet range to 1350 nm in the near infrared range have been detected using a 416 nm pitch grating. We used a single tip Si field emitter as an electron source and the input power level was low such as beam currents of 20-200 nA and acceleration voltages of 25-34 W Emission peaks in the Smith-Purcell radiation blueshift with increasing the acceleration voltage and coincide with the theoretical ones. (c) 2006 American Vacuum Society.