Researchers at Strathclyde University and Capital Normal University in Beijing are collaborating on the development of a new terahertz (THz) radiation source that could offer a less harmful alternative to x-rays.
THz radiation is far-infrared electromagnetic radiation that has a frequency between 0.1THz and 10THz (1THz = 10^12Hz), which fits between the mid-infrared and microwave spectra.
Unlike visible light, radiation penetrates materials such as plastic, cardboard, wood and composite materials, and is a promising replacement for X-rays used in imaging and security.
The vibrational and rotational spectral fingerprints of large molecules coincide with the THz band, which makes THz spectroscopy a powerful tool for identifying hazardous substances, such as drugs and explosives.
THz radiation is important for biology and medicine because many biological macromolecules, such as DNA and proteins, have their collective motion at THz frequencies. It can also be used to uncover the intricacies of semiconductors and nanostructures, and therefore are important tools for developing new electro-mechanical devices and solar cells.
Many different methods of generating THz radiation exist, including driving photocurrents in semiconductor antennas, excitation of quantum wells and optical rectification in electro-optic crystals. However, their maximum power is restricted because of damage to the optical materials at high powers. The use of Plasma acceleration to accelerate charged particles has long been viewed as an attractive alternative.
Led by Strathclyde’s Prof Dino Jaroszynski, the group has shown experimentally that unprecedentedly high-charge bunches of relativistic electrons can be produced by a laser wakefield accelerator (LWFA). These are produced in addition to the usual high-energy, low-charge beams that are emitted.
The team showed that when an intense ultra-short laser pulse is focussed into helium gas, a plasma bubble moving at the nearly the speed of light is formed. These high-charge beams of electrons are distinct from the usual low-charge (picocoloumb), high-energy (100s MeV to GeV), femtosecond duration electron bunches that are commonly observed from the LWFA.
Prof Jaroszynski, who is the director of the Scottish Centre for the Application Plasma-based Accelerators (SCAPA), project, said: “This is an unprecedented efficiency at these THz energies. The increasing availability of intense THz sources will lead to completely new avenues in science and technology.
“New tools for scientists lead to new advances. The interaction of intense THz radiation with matter allows access to nonlinear processes, which enables the identification of normally hidden phenomena, and also unique control of matter, such as aligning molecules using high THz fields or distorting band structure in semiconductors.