Terahertz radiation can be useful in many applications including spectroscopy, communications, astronomy and imaging through objects and tissue for security and medical purposes. However, radiation in this particular wavelength range has been more challenging to generate than other forms that can be produced using ordinary LEDs, lasers or transistors, typically requiring advanced and energy-intensive optical systems that require special temperature conditions or take up a substantial amount of space. Now, engineers at the Vienna University of Technology have developed a much simpler, extremely compact source of terahertz radiation that can operate at room temperature, opening up the possibility for more affordable, accessible and portable devices to leverage this technology.
The new source, which is less than 1 mm in size, incorporates an oscillator with double resonant-tunneling diodes (RTDs). The RTDs were designed with particularly narrow quantum wells allowing only very few, specific electron states to exist between tunnel barriers, explained first author Petr Ouředník. The design enables negative electrical resistance in the oscillating circuit, causing the circuit to gain energy as voltage is increased and allowing external direct current to be converted into terahertz radiation through continued electromagnetic oscillations, said corresponding author Michael Feiginov. In addition to its simplicity and compact size, the device produces a considerably high intensity of terahertz radiation. This work was published in Applied Physics Letters.
“There are so many application ideas that we can’t even say today which one is the most realistic,” said Feiginov. “The terahertz range is used in radio astronomy, one can use it to see through optically opaque objects, for example in security checks at the airport or even in material testing. Another exciting application are chemical sensors: different molecules can be recognized by the fact that they absorb very specific frequencies in the terahertz range. All these technologies will benefit from simple and compact terahertz sources, and that’s what we wanted to make an important contribution to.”
The researchers note in their paper that the radiation source could produce even higher operating frequencies and output powers through further optimization of RTD parameters and other components.
Photo: First author Petr Ouředník in the lab. Credit: Vienna University of Technology