New Terahertz Beam Lasers Can Now Operate Outside of Labs

The high-power, portable terahertz laser could prove useful in medical imaging and contraband detection, among other things.
Fabienne Lang

The quantum cascade laser is seeing its next-generation thanks to MIT and the University of Waterloo researchers. 

Now, it's portable, high-powered, and can generate terahertz outside of a laboratory environment. This development will make it extremely useful in settings such as hospitals and airports for detecting skin cancers and hidden contraband, for instance. 

The team has managed to create a device that doesn't require the usually-extremely-cold temperatures it needs to operate, meaning it can be transported to other settings. 

Their study was published in Nature Photonics on Monday.


Terahertz radiation

In order to carry out real-time imaging and fast spectral measurements using terahertz radiation, you needed temperatures as low as 200 kelvins, or -100 degrees Fahrenheit (-73 degrees Celcius). That was true until now.

Thanks to the team of researchers, this process can now happen at 250 kelvins, -10 degrees Fahrenheit (-23 degrees Celcius). So instead of requiring bulky equipment in a lab, it's now possible to carry out the same work in different locations with the use of a compact portable cooling system. 

The new tech is being used on terahertz quantum cascade lasers, which are" tiny chip-embedded semiconductor laser devices," as the researchers put it. These lasers have been around since 2002, and researchers have been trying to find ways to increase the temperatures needed to operate them. 

New Terahertz Beam Lasers Can Now Operate Outside of Labs
A scanning electron microscope photo of a terahertz quantum cascade laser device. Source: MIT

"This will enable portable terahertz imaging and spectral systems that will have an immediate impact on wide-ranging applications in medicine, biochemistry, security, and other areas," said Qing Hu, one of the paper's authors and MIT Distinguished Professor of Electrical Engineering and Computer Sciences.

The team's lasers are only a few millimeters in length and are thinner than hair. They are called 'cascade' lasers because electrons 'cascade' down a sort of staircase, and in doing so emit a light particle at each step. 

The way the team managed to lower the temperature needed to operate these lasers was by doubling the height of the barriers in the laser so as to prevent leakage of the electrons, something that increases at higher temperatures. 

"We understood that over-the-barrier electron leakage was the killer," which meant the system would break down if not cooled with a cryostat, Hu explained. "So, we put a higher barrier to prevent the leakage, and this turned out to be key to the breakthrough."

The team is positive with the new discovery and believes it can push through so as to create powerful terahertz without using a cooler at all. 

As Hu mentioned, "Using the direct phonon scheme and taller barriers is the way to go forward. I can finally see the light at the end of the tunnel when we will reach room temperature."

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