Researchers at Columbia University in New York and NEC Research Institute in Princeton, N.J., have demonstrated two-dimensional terahertz imaging using two slightly detuned continuous-wave diode lasers that serve as the optical source for both signal generation and detection. The process, which uses off-the-shelf laser diodes as opposed to costly ultrafast lasers, produces the terahertz signal by nonlinearly mixing the two diode laser beams in a photoconductive emitter.Detection is performed using a ZnTe electro-optic crystal to coherently upconvert a terahertz signal into the optical part of the spectrum, where it can be imaged using a standard CCD. The scientists' proof-of-concept experiment was reported in the Aug. 5 issue of Applied Physics Letters.