Researchers create compact room temperature THz source
Devices using terahertz waves can detect explosives, chemical agents, and dangerous biological substances from safe distances. In astronomical research, atomic and molecular emission lines in the THz range are key diagnostic probes of the interstellar medium. But current terahertz sources are large, multi-component systems that sometimes require complex vacuum systems, external pump lasers, and even cryogenic cooling.
"A single-component solution capable of room temperature and widely tunable operation is highly desirable to enable next generation terahertz systems," said Manijeh Razeghi, director of Northwestern's University's Centre for Quantum Devices who, with her team, has been working to develop such a device.
In a recent paper in Applied Physics Letters, they demonstrate a room temperature, highly tunable, high power terahertz source. The monolithic design (pcitured above) is based on three-section Sampled Grating Distributed Feedback - Distributed Bragg Reflector (SGDFB-DBR) design in a mid-infrared quantum cascade laser . Sampled grating design has been widely applied to the semiconductor lasers at telecom wavelengths to extend their monolithic tuning range.
Based on nonlinear mixing in quantum cascade lasers, the group's THz source can emit up to 1.9 milliwatts of power and has a frequency coverage of 1 to 4.6THz. By designing a multi-section, sampled-grating distribution feedback and distributed Bragg reflector waveguide, Razeghi and her team were also able to give the device a tuning range of 2.6 to 4.2THz at room temperature.
"I am very excited about these results," Razeghi said. "No one would believe any of this was possible, even a couple years ago."
'Widely tunable room temperature semiconductor terahertz source' by Q Y Lu et al is published in Applied Physics Letters 105, 201102 (2014); http://dx.doi.org/10.1063/1.4902245