A micro-fabricated sheet-beam Orotron THz source

We describe the fabrication of an Orotron driven by a sheet beam of electrons. The sheet beam is generated by a carbon nanotube field emission electron gun, which is less than 2 mm in total thickness. The orotron cavity is 2 cm long and 1 cm wide, and houses a microfabricated Smith-Purcell grating which generates the THz radiation. The sheet beam is 5 mu m thick and 6 mm wide, and it travels within 15 mu m of the top surface of the Smith-Purcell grating for the length of the cavity. The Orotron is discretely tunable, which means that there are a number of cavity resonances that can be driven by changing the energy of the beam such that for the period of the Smith-Purcell grating the cavity is driven on one of the resonances. For this work, a target frequency of 0.5 THz, corresponding to a beam energy of 3 keV, was used.