Posted in | Laser

A New Technique to Control Laser Polarization

Artist's depiction of the laser polarization metasurface that can tune the laser's polarization state purely electronically, without any moving parts. (Credit: Nicoletta Barolini/UCLA)

A UCLA-led team has developed a new method to control laser polarization which could pave the way for a new generation of powerful and high-quality lasers. Such lasers can prove useful in chemical sensing and detection, medical imaging, or fundamental science research.

Polarized sunglasses allow people to see more clearly in strong, intense light. A polarizing phenomenon operates by filtering visible light waves so that only waves that have their electric field pointing in a particular direction can pass through, thus reducing glare and brightness.

Similar to color and brightness, polarization is a key property of light that originates from a laser. In the standard technique, the polarization state of a laser is tuned or controlled by using a separate component like a waveplate or a polarizer. In order to change its polarization, the waveplate or polarizer has to be physically rotated, but this process is very slow and leads to a physically larger laser system.

The research group from the UCLA Henry Samueli School of Engineering and Applied Science has now created a new artificial material, a type of “metasurface,” that can adjust the polarization state of the laser electronically, with no moving parts. The study has been reported in Optica. The breakthrough development was used on a group of lasers in the terahertz range of frequencies on the electromagnetic spectrum, which lies between infrared and microwaves waves.

While there are a few ways to quickly switch polarization in the visible spectrum, in the terahertz range there is currently a lack of good options. In our approach, the polarization control is built right into the laser itself. This allows a more compact and integrated setup, as well as the possibility for very fast electronic switching of the polarization. Also, our laser efficiently generates the light into the desired polarization state - no laser power is wasted generating light in the wrong polarization.

Benjamin Williams, Associate Professor of Electrical Engineering, UCLA

Williams added that terahertz radiation can enter into a wide range of materials, such as paints, plastics, foams, dielectric coatings, packaging materials, etc. without damaging them.

So some applications include non-destructive evaluation in industrial settings, or revealing hidden features in the study of art and antiquities. For example, our laser could be used for terahertz imaging, where the addition of polarization contrast may help to uncover additional information in artwork, such as improved edge detection for hidden defects or structures.

Benjamin Williams, Associate Professor of Electrical Engineering, UCLA

The study is based on the team’s latest development of the world’s first vertical-external-cavity surface-emitting laser (VECSEL) that works in the terahertz range.

The new metasurface features a clear zigzag pattern of wire antennas that run across its surface, and covers an area of 2 mm2 square millimeters. An electric current running through the wires selectively energizes specific parts of the laser material, enabling users to alter and customize the polarization state as desired.

The research’s lead authors are electrical engineering graduate student Luyao Xu and electrical engineering undergraduate student Daguan Chen. Other authors include Mohammad Memarian, a postdoctoral scholar in UCLA’s microwave electronics lab; electrical engineering graduate student Christopher Curwen; UCLA electrical engineering professor Tatsuo Itoh, who holds the Northrop Grumman Chair in Engineering; and John Reno of Sandia National Laboratories.

The National Science Foundation and NASA supported the research.

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