Researchers from the University of Electrocommunications in Tokyo and NEC Corp. in Kanagawa, Japan, have produced terahertz radiation with an energy density of 10 µJ/cm2 from a photoconductive semiconductor antenna. Using 0.5-ps pulses from a 248-nm, 10-mJ KrF laser system, the team produced the high energy density by inducing coherently added emissions from more than 2000 photoconductive gaps on the chip. A chemical vapor-deposited film provided a threshold breakdown in the gaps high enough for an electric field stress of 2 x 106 V/cm to be applied.The team, reporting in the Dec. 20 issue of Applied Optics, predicted that, by using a higher laser intensity, electric field and emission area, a focused intensity of several hundred megawatts per square centimeter may soon be achieved.