Jiangsu Laser Union Introduction: Researchers from MIT and the University of Waterloo have developed a high-power, portable laser device called a tuned quantum cascade laser, a type of laser that can generate terahertz lasers outside of the lab. The laser could potentially be used in applications such as skin cancer localization and detection of hidden explosives . The results were published in the recent issue of Nature.
Tuned quantum cascade laser developed to generate terahertz lasers
Until today, generating terahertz lasers with sufficient power enabled real-time imaging and rapid spectroscopic measurements of temperatures at temperatures below 200 K or lower. These temperatures can only be achieved by an overall temperature drop in the device, limiting the technology to laboratory use only. In the recent topical issue of Nature, Qing Hu, a distinguished professor of electrical engineering and professor of computational science from MIT, and colleagues report on their quantum cascade laser, which can be realized to operate at for temperatures higher than 250 K, meaning that only a removable cooling system is required.
Terahertz quantum cascade lasers, embedded in microchips and semiconductor laser devices, were first invented in 2002, but until the technology could be adapted to work at temperatures higher than 200K proved to be very difficult, as physical reasons in this area prevented this from being achieved, Hu said.
By working at a higher temperature, we can finally apply the technology in a compact and mobile system and make a breakthrough in this area, and apply it outside the lab, Hu said, which would allow mobile terahertz imaging and spectroscopy systems to be used immediately in a wide range of applications such as healthcare, biochemistry, security, and other fields.
Hu began studying terahertz frequencies, a band of the electromagnetic (wave) spectrum between the microwave and infrared ranges, back in 1991.
This research took us 11 years and three generations of students, and resulted in our terahertz cascade laser in 2002, he said, noting that since then, the highest limiting operating temperatures have been the biggest obstacle limiting our use of terahertz lasers, which essentially remain below room temperature. The maximum temperature of 250 K reported in this paper is considered to be a major step forward from the earlier 210 K. This result of an operating temperature of 210 K was obtained in 2019, and this result is a step forward from the temperature of 200 K achieved in 2012, an advance that took seven years.
This laser, which measures targets that are only a few millimeters long and thinner than a human hair,
we understand that above the barrier of electron leakage is a big killer for this laser, belonging to quantum well structures and finely tailored to engineering and barriers. Within these structures, the electrons descend like a waterfall and form a step-like structure that emits a light particle or photon at each step.
A very important innovation described in the journal Nature Photonics is the laser multiplication of the height of the barriers to stop the leakage of electrons, which is a phenomenon used to achieve an increase at higher temperatures. We understand that above the barrier where the electrons are leaking, causing problems in the system if it can't be cooled by a cryostat, Hu said, the more popular view is that scattering, along with high barriers, is damaging, so high barriers need to be avoided.
The team developed the right parameters for the energy band structure, which is used for high barriers and new designs.
The biggest contribution of the research team was in the simulation and fabrication of quantum devices, which led to very important advances in the problems faced in the challenge of THz photons.
In a medical setup, the new mobile laser system, which includes a compact camera and detector that can be used anywhere there is an electrical outlet, enables real-time imaging of routine skin scans or in-surgery practice of skin cancers, which show up very well in terahertz lasers due to the fact that they contain a high concentration of water and blood compared to regular cells.
This technique is very effective.
This technology can also be used in many industrial applications, wherever there is a need to detect foreign objects, and the products detected need to be safe and of good quality.
The detection of gases, drugs, and explosives is one of the more complex aspects of using terahertz lasers. For example, compounds such as hydroxide, an ozone depleting agent, have a specific spectral fingerprint at terahertz laser frequencies, and for drugs, including heroin, and explosives such as TNT.
In a medical setting, the new portable system, which includes a compact camera and detector and can operate in the field, is a good example of how to use a terahertz laser. In a medical setting, the new portable system, which includes a compact camera and detector and can operate anywhere with an electric outlet, could provide real-time imaging during regular skin-cancer screenings or even during surgical procedures to excise the skin. The cancer cells show up "very dramatically in terahertz" because they have higher water and blood concentrations than normal cells, Hugh's cancer cells are more sensitive to the effects of cancer than normal cells. The cancer cells show up "very dramatically in terahertz" because they have higher water and blood concentrations than normal cells, Hu says.
The technology could also be applied in many industries where the detection of foreign objects within a product is necessary to assure the safety of the product. The technology could also be applied in many industries where the detection of foreign objects within a product is necessary to assure its safety and quality.
Detection of gases, drugs, and explosives could become especially For example, compounds such as hydroxide, an ozone-destruction agent, have a special spectral " fingerprint" within the terahertz radiation. fingerprint" within the terahertz frequency rage, as do drugs including methamphetamine and heroin, and explosives including TNT.
Utilizing room temperature pyroelectric detectors
With terahertz lasers, we can not only observe optically opaque materials (blackbody materials), but we can also identify matter," Hu said. He also said that terahertz lasers can be generated without the need for a cooling system, allowing clear visualization of targets
From: High-power portable terahertz laser systems, Nature Photonics (2020). DOI: 10.1038/s41566-020-00707-5 , www.nature.com/articles/s41566-020-00707-5