Novel laser produces random mid-infrared light for improved imaging applications

Feb 26, 2014
Novel laser produces random mid-infrared light for improved imaging applications
Random lasers remove speckling while maintaining brightness and could be used for applications where imaging quality is important, such as checking mail or airport security. Credit: Tomasz Wyszołmirski/iStock/Thinkstock

Most lasers produce coherent light, meaning that the light waves are perfectly synchronized with each other. Spatially coherent waves, however, can interfere with one another and produce speckles in an image. With this in mind, scientists are turning to so-called random lasers, which not only show promise for applications such as biological and environmental imaging, but also mimic natural, disordered scattering from objects such as clouds.

Hou Kun Liang and co-workers at the A*STAR Singapore Institute of Manufacturing Technology and Nanyang Technological University, Singapore, have now developed a random laser that emits light in the mid-infrared range1. Moreover, the random laser is driven by electricity, making it more suitable for practical applications.

"Most are driven by optical pumping—this requires another laser to excite the random media," says Liang. "With electrical pumping we can make the laser smaller, less complex and cheaper."

The researchers modified a design known as a quantum cascade laser that contains several thin layers of compound semiconductors. When an external voltage is applied, electrons are driven across the layers and emit photons at every step. The frequency of the emitted light can be controlled by adjusting the thickness of the layers.

"A is like an electron reservoir," says Liang. "After an electron relaxes to a lower energy level, instead of becoming inactive, it flows to the subsequent active region where it is 're-used'. This is important for our laser, because loss in the mid-infrared region is high, and so we need a high gain to compensate for it."

Crucially, Liang and co-workers used plasma etching to create a random pattern of small holes—each only three micrometers in diameter—on the top surface of their laser. This design causes the laser light to be randomly scattered before it is emitted through the holes.

Currently, the random laser must be cooled to very low temperatures using liquid nitrogen to maximize the gain, but Liang and co-workers anticipate that their design can be improved to reduce the loss of mid-infrared radiation at room temperature. Liang also points out that their design gives them great freedom to explore other laser frequencies.

"For example, terahertz lasers can penetrate thick plastics and papers and, unlike X-rays, are harmless to humans. These lasers could be used for applications, such as checking mail or airport security, where imaging quality is important—a random would remove speckling while maintaining brightness."

Explore further: Optical 'dog's nose' may hold key to breath analysis

More information: Liang, H. K., Meng, B., Liang, G., Tao, J., Chong, Y. et al. "Electrically pumped mid-infrared random lasers." Advanced Materials 25, 6859–6863 (2013). DOI: 10.1002/adma.201303122

Related Stories

Harnessing randomness to improve lasers

Jan 15, 2014

Randomly arranged items usually have poor optical properties. The rough—or random—surface of a frosted-glass window, for example, obscures the view of an object. The optical industry therefore expends ...

Taking the 'random' out of a random laser

Jul 15, 2013

( —Random Lasers are tiny structures emitting light irregularly into different directions. Scientists at the Vienna University of Technology have now shown that these exotic light sources can be ...

Diagnosis just a breath away with new laser

Jan 31, 2014

( —University of Adelaide physics researchers have developed a new type of laser that will enable exciting new advances in areas as diverse as breath analysis for disease diagnosis and remote sensing of critical ...

Laser-induced damage in focus

Jan 17, 2014

The transformation of infrared light to a different wavelength, such as visible light, is important in many applications. Some of the most efficient semiconductor lasers operate in the infrared region of ...

Recommended for you

Optical 'dog's nose' may hold key to breath analysis

12 hours ago

University of Adelaide researchers are developing a laser system for fast, non-invasive, onsite breath analysis for disease, potentially enabling screening for a range of diseases including diabetes, infections and various ...

Could your smartphone one day tell you you're pregnant?

Jul 01, 2015

Researchers at the Hanover Centre for Optical Technologies (HOT), University of Hanover, Germany, have developed a self-contained fiber optic sensor for smartphones with the potential for use in a wide variety ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.