Introduction to Jiangsu Laser Alliance: Researchers from MIT and the University of Waterloo have developed a high-power, movable laser device called a tunable quantum cascade laser. This type of laser can be used in the laboratory Externally generated terahertz laser. Lasers could have potential applications such as locating skin cancer and detecting hidden explosives. This result was published in the recently published "Nature".
The developed tunable quantum cascade laser that can produce terahertz laser
Until today, terahertz laser that generates enough power can achieve real-time images and temperatures below 200K or more Fast spectral measurements at low temperatures. These temperatures can only be achieved by reducing the overall temperature of the device, limiting the technology to laboratory use. In the recently published top issue of Nature, Qing Hu, a distinguished professor of electrical engineering and computing science from MIT, and his colleagues reported that their quantum cascade laser can operate at temperatures higher than 250K. This means that only a removable cooling system is sufficient.
Terahertz quantum cascade lasers, semiconductor laser devices embedded in microchips, were first invented in 2002, but until the technology could be adapted to operate above 200K it proved very difficult because of the Physics in the field prevent this goal from being achieved, Hu said.
By working at a relatively high temperature, we can eventually apply this technology in compact and mobile systems and achieve breakthroughs in this field, while applying it outside the laboratory, Hu Said that this will make mobile terahertz imaging and spectroscopy systems immediately available in a wide range of applications, such as medicine, 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 the continuous efforts of three generations of students made our terahertz cascade laser come out in 2002. He said that from then on, the highest limit operating temperature It has become the biggest obstacle limiting our use of terahertz lasers, which are basically maintained below room temperature. The maximum temperature reported in this paper is 250 K, which is considered a big step forward from the earlier 210 K result obtained in 2019 for an operating temperature of 210 K, which was achieved in 2012 This progress was based on 200K and took 7 years.
This laser can measure a target with a length of only a few millimeters and a thickness thinner than a human hair.
We understand that there is a need for this laser to overcome the barrier of electron leakage. It is said to be a big killer, a quantum well structure and finely customized engineering and obstacles. Within these structures, electrons cascade down to form a step-like structure, emitting a light particle, or photon, at each step.
A very important innovation was described in the journal "Nature Photonics", which is to prevent the leakage of electrons by increasing the height of the laser multiplication barrier. This is a phenomenon used to achieve an increase at higher temperatures. . We understand that the barrier of electron leakage will cause problems in the system. If a cryostat cannot be used for cooling, Hu said that the more popular view is scattering. At the same time, high barriers are accompanied by damage, so high obstacles to avoid.
The research team developed the correct parameters for the band structure, which is used for high barriers and new designs.
The biggest contribution of the research team lies in the simulation and manufacturing of quantum devices, which has made very important progress in the challenges of THz photons.
In a medical setting, the new mobile laser system, which includes a compact camera and detector that can be used anywhere there is an outlet, can enable real-time imaging of routine skin scans or In the practice of skin cancer during surgery, these cancer cells show up very clearly in the terahertz laser because they contain high concentrations of water and blood than regular cells.
This technology can be applied in many industrial fields at the same time, as long as it is necessary to detect foreign objects, and the detected products need to ensure safety and quality.
Detecting gases, drugs and explosives has become a more complicated matter using terahertz lasers. For example, compounds such as hydroxide, an ozone depleting agent, have specific spectral fingerprint information at terahertz laser frequencies, as well as 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 anywhere with an electric outlet, could provide real-time imaging during regular skin-cancer screenings or even during surgical procedures to excise skin cancer tissues. 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 its safety and quality.
Detection of gases, drugs, and explosives could become especially sophisticated with the use of terahertz radiation. For example, compounds such as hydroxide, an ozone-destruction agent, have a special spectral "fingerprint" within the terahertz frequency rage, as do drugs including methamphetamine and heroin, and explosives including TNT.
Using room temperature pyroelectric detectors and TH in Camera measurement device for TEC-cooled THZ QCL
Using terahertz laser, we can not only observe optically opaque materials (black body materials), but also identify substances. Hu said. He also said: Terahertz laser can be generated without the need for a cooling system, so that the target can be clearly observed
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