More Power for Terahertz Lasers

Scanning electron microscope image of the terahertz quantum cascade laser (Source: Wang et al. / AIP Advances)

Scanning electron microscope image of the terahertz quantum cascade laser (Source: Wang et al. / AIP Advances)

Researchers have nearly doubled the conti­nuous output power of a tera­hertz quantum cascade laser, with potential appli­cations in medical imaging, airport security and more. Increasing the continuous output power of these lasers is an important step toward increasing the range of practical appli­cations. Terahertz radia­tion sits between microwaves and infrared light on the electro­magnetic spectrum. It is relatively low-energy and can penetrate materials such as clothing, wood, plastic and ceramics. The unique qua­litites of terahertz radiation make it an attrac­tive candidiate for imaging, but the ability to produce and control terahertz waves has lagged behind techno­logy for radio, microwave and visible light.

Recently, scientists have made rapid progress on a techno­logy to produce terahertz light called a quantum cascade laser or QCL. Quantum cascade lasers are made from thin layers of material. The thin layers give the laser the valuble property of tuna­bility, meaning the laser can be designed to emit at a chosen wavelength. The output power of tera­hertz QCLs is also relatively high compared to other tera­hertz sources, said Xuemin Wang, a researcher in the China Academy of Enginee­ring Physics.

Wang and his colleagues’ work focuses on even further increa­sing the output power of tera­hertz quantum cascade lasers, especially in the mode in which the laser output power is continuous. “In engineering, bio­mechanics and medical science, the applications require continuous wave mode,” Wang said. By optimizing the material growth and manu­facturing process for tera­hertz QCLs, Wang and his team made a laser with a record output power of up to 230 milliwatts in continuous wave mode. The previous record was 138 milli­watts.

Wang said the new 230 milli­watt laser could be used in air, a challenge for lower-powered lasers since particles in the air can scatter or absorb the laser light before it reaches its target. The increase demon­strates that the team’s method of precisely controlling the growth of the laser’s layers can increase output power, Wang said, and he is hopeful that future improve­ments could bring the continuous power above 1 watt. The 1 watt level has been reached in tera­hertz QCLs in pulsed wave mode. Wang said he thinks scientists and engineers could use the new laser as a flexible source of tera­hertz radiation for spectros­copy, medicial imaging, remote sensing and other appli­cations. (Source: AIP)

Reference: X. Wang et al.: High-power terahertz quantum cascade lasers with ~0.23 W in continuous wave mode, AIP Adv.; online July 26 2016; DOI: 10.1063/1.4959195

Link: Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang Sichuan, China

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