http://www.digitaljournal.com/tech-and-science/science/laser-used-to-wirelessly-charge-a-smartphone/article/515522

Laser used to wirelessly charge a smartphone

Posted Feb 21, 2018 by Tim Sandle
Physicists have used a laser to wirelessly charge a smartphone. This was achieved safely and using the distance of a typical room.
Graphene enables ultrafast laser pulses for spectroscopy and biomedical applications.
Graphene enables ultrafast laser pulses for spectroscopy and biomedical applications.
Andrew Adams
The engineering feat, from the University of Washington, represents the fist time a method has been developed to safely charge a smartphone wirelessly using a laser. This addresses a major issues with smart devices. While the devices work wirelessly they need to be plugged in so that their batteries charge. Batteries with a relatively low time span is a major frustration for business and personal users of smartphones and tablets.
With the technology, the charging beam is generated by a laser emitter. The laser is configured to produce a focused beam in the near-infrared spectrum. As the laser reaches a smartphone, special 3D printed "retroreflectors", which have been placed around the power cell on a smartphone, reflect the guard beams back to photodiodes on the laser emitter.
In trials using a prototype model the new laser method can potentially charge a standard smartphone as rapidly as a standard USB cable. According to lead researcher Professor Shyam Gollakota: "We have designed, constructed and tested this laser-based charging system with a rapid-response safety mechanism, which ensures that the laser emitter will terminate the charging beam before a person comes into the path of the laser."
The laser used for the charging is normally colorless; however, for demonstration purposes the researchers used red beams. A video demonstrating the technology has been uploaded by the researchers onto Facebook.
The use of lasers carries potential safety issues. To overcome these the researchers inserted a metal, flat-plate heatsink on the test smartphone. This was to dissipate excess heat from the laser. An additional safety feature was in the form of a reflector-based mechanism, which shuts off the laser if a person attempted to move in the charging beam's path.
The research has been published in the new journal Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies. The peer reviewed paper is titled "Charging a Smartphone Across a Room Using Lasers."