Researchers at Lehigh Photonics and Nanoelectronics Center have achieved a record high output power of terahertz lasers by using a new phase-locked technology, and reported the highest radiation efficiency of any single-wavelength semiconductor quantum cascade laser.
Terahertz lasers may appear soon. The radiation emitted by terahertz laser is between microwave and infrared light in the electromagnetic spectrum. Because they can penetrate common packaging materials (such as plastics, fabrics and cardboard) and can be used to identify and detect various electromagnetic waves, they have always been the focus of research. Chemicals and biomolecules can even image some types of biological tissues without causing damage. The potential of terahertz laser lies in improving its intensity and brightness by improving power output and beam quality.
Now, Kumar, Jin and John L. Reno of Sandia have reported another breakthrough of terahertz technology: they have developed a new phase-locked technology of plasma laser, and used this technology to achieve a record high-power output of terahertz laser. Their laser produces the highest radiation efficiency of any single-wavelength semiconductor quantum cascade laser. These results are explained in the paper "Phase-locked terahertz plasmon laser array with output power of 2 W in single spectral mode" published by Optica on June 2, 2020/KLOC-0.
Kumar said: "As far as we know, the radiation efficiency of terahertz laser is the highest demonstrated by any single-wavelength QCL so far, and it is also the first report that this QCL achieves more than 50% radiation efficiency." . "Such a high radiation efficiency exceeds our expectations, which is one of the reasons why our laser output power is significantly higher than the previous power."
In order to improve the optical power output and beam quality of semiconductor lasers, scientists often use phase-locked technology, which is an electromagnetic control system that can force a series of optical cavities to emit radiation during the locking step. Terahertz QCL uses a metal-coated optical cavity to limit light. It is a kind of laser called plasma laser, which is famous for its poor radiation performance. They said that the number of technologies available in the existing literature is limited, and these technologies can be used to greatly improve the radiation efficiency and output power of this plasma laser.
Jin said: "Our paper describes a new plasmon phase-locked scheme, which is obviously different from the previous research on phase-locked lasers in a large number of semiconductor laser literature." The proven method uses the propagating surface wave of electromagnetic radiation as a tool for phase locking of plasma optical cavity. By realizing the record high output power of terahertz laser, it is an order of magnitude higher than the previous work, which proves the effectiveness of this method. "
Surface wave propagating along the metal layer of the cavity but in the surrounding medium instead of inside the cavity is a unique method developed by Kumar research group in recent years, which will continue to innovate to further explore new ways. The team predicts that the output power level of their lasers can lead to cooperation between laser researchers and applied scientists to develop terahertz spectroscopy and sensing platforms based on these lasers.
This innovation of QCL technology is the result of long-term research in Lihai by Kuhai Laboratory. Kumar and Jin put forward the idea of final realization through about two years of design and experiment. The cooperation with Dr. Reynolds of Sandia National Laboratory enabled Kumar and his team to receive semiconductor materials and form quantum cascade optical media for these lasers.
According to the researchers, the main innovation of this work lies in the design of optical cavity, which has nothing to do with the performance of semiconductor materials to some extent. They said that the newly acquired inductively coupled plasma (ICP) etching tool of Lihai CPN Company played a key role in pushing the performance limit of these lasers.
Kumar said that this research represents how to develop narrow-beam single-wavelength terahertz lasers and will be developed in the future, which is a paradigm shift. He added: "I think the future of terahertz lasers looks very bright."