Terahertz imaging with nonlinear quantum-cascade-laser source

We demonstrate terahertz imaging using a terahertz nonlinear quantum cascade laser source (THz NL-QCL). THz NL-QCLs are ultrabroad terahertz source which can be operated at room temperature. The maximum operating temperature of conventional THz-QCLs has been limited to 210.5 K so far. Therefore, THz NL-QCL sources are the only electrically pumped monolithic terahertz semiconductor sources operable at room temperature. Currently, various room temperature compact THz sources have been reported. However, the operation frequencies of these sources were basically below 1 THz. Although several devices demonstrate THz emission above 1THz, output powers are still quite low; thus, it is very difficult to apply to practical THz applications. THz NL-QCL sources are able to operate above 1 THz, and the average THz output powers have exceeded 10 μW (duty cycle >5%) at room temperature, which can potentially be applied to THz applications. Also, in edge-emitting metal-metal THz QCLs, ring-like fringe patterns in their far-field beams are frequently observed due to far-field interference of coherent radiation in deep sub -wavelength apertures. Otherwise, the beam profile of THz NLQCL is Gaussian-like far-field pattern. The beam quality of nonlinear quantum cascade laser is better than that of conventional terahertz quantum cascade laser. Therefore, THz NL-QCL sources are suitable for terahertz imaging. We demonstrated terahertz imaging with the THz NL-QCL sources.