New type of metasurface allows unprecedented laser control

To project complex holograms, the shape of the laser beam can also be controlled. Credit: Christina Spgele/Harvard SEAS Many of today's technology relies on the ability to control the properties of laser light. This is true for everything from commercial VR headsets to microscopy for biomedical research. Today's laser systems are heavy and complicated because they rely on rotating parts to control the power, wavelength and shape of the laser beam. Researchers at Harvard John A. Paulson School of Engineering and Applied Sciences now have a single metasurface that is capable of tuning the various properties of laser light without the use of optical components. The metasurface can divide light into multiple beams, and control their intensity and shape in an independent, precise, and efficient way. This research has opened the doors to lightweight, efficient optical systems that can be used for a variety of applications, including quantum sensing and VR/AR headsets. Federico Capasso is the Robert L. Wallace Professor in Applied Physics and Vinton Hayes Senior Fellow in Electrical Engineering at SEAS. He was also the senior author of this paper. Nature Communications published the research recently. Only two components make up the tunable laser: a laser diode, and a reflective surface. This surface uses supercells instead of the previous metasurfaces that relied on individual pillars to control light. Instead, it uses a group of pillars that work together to control different aspects. The incident light can be divided into three distinct beams with different properties. These are a conventional beam (right), Bessel beam (center) or an optical vortex. Credit: Christina Spgele/Harvard SEAS The diode emits light that hits the metasurface's supercells. A portion of this light is reflected back to create a laser cavity. The second part of the light is reflected back into a beam that is separate from the first. Christina Spgele, a graduate student in SEAS, and the first author of this paper, stated that different colors are deflected when light hits the metasurface. "We were able to harness this effect, and designed it so that the wavelength we chose has the correct direction to enter the diode. This allows the laser to only operate at that wavelength. Researchers can change the wavelength by simply moving the metasurface relative to the laser diode. Michele Tamagnone (ex-postdoctoral fellow at SEAS, co-author of this paper) stated that the design was more compact and simple than other wavelength-tunable lasers. Researchers also demonstrated that the shape and projection of a laser beam can be controlled in order to project complex holograms, such as the century-old Harvard shield. The researchers also showed that they could split the incident light into three distinct beams with different properties. These beams were a conventional beam, an optical vortex, and a Bessel beam. This beam looks like a bullseye, and can be used in many applications, including optical tweezing. Capasso stated, "In addition to controlling all types of lasers, this ability generate multiple beams in parallel, directed at arbitrary angles and each implementing an individualized function will allow many applications, from scientific instrumentation, augmented or virtual reality, and holography." Continue exploring Metasurface's world of polarization Christina Spgele and colleagues, Multifunctional wide angle optics and lasing that are based on supercell-derived metasurfaces, Nature Communications (2021). Information from Nature Communications Christina Spgele and colleagues, Multifunctional wide angle optics and lasing that are based on supercell-metasurfaces. Journal information: Nature Communications. DOI: 10.1038/s41467-224071-2

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