In a series of recent tests, the Persistent Optical Wireless Energy Relay (POWER) program achieved several records for transmitting power over distance. The team recorded more than 800 W of power delivered during a 30-s transmission from a laser 8.6 km away. Over the course of the test campaign, more than 1 MJ of energy was transmitted. Previously, the greatest reported distance records for an appreciable amount of optical power (>1 μW) were 230 W of average power at 1.7 km for 25 s and a lesser (but undisclosed) amount of power at 3.7 km. In the optical power beaming receiver designed for PRAD (POWER Receiver Array Demo), the laser enters the center aperture, strikes a parabolic mirror, and reflects onto dozens of photovoltaic cells arranged around the inside of the device which convert the energy back to usable power. Courtesy of DARPA. The DARPA-led team brought together industry and government, including the U.S. Naval Research Laboratory and the High Energy Laser Systems Test Facility (HELSTF) at the U.S. Army’s White Sands Missile Range. These tests, referred to as PRAD (POWER Receiver Array Demo), mark an important step toward the POWER program’s long-term goal of being able to instantly beam power from a location where it can be easily generated to wherever it’s needed, opening a novel design space for platform capabilities unbounded by fuel limitations. To achieve the power and distance records, PRAD used a receiver technology with a compact aperture for the laser beam to shine into, ensuring very little light escapes once it has entered the receiver. Inside the receiver, the laser strikes a parabolic mirror that reflects the beam onto dozens of photovoltaic cells to convert the energy back to usable power. The receiver was designed by Teravec Technologies, led by principal investigator Raymond Hoheisel, with support from Packet Digital and the Rochester Institute of Technology. According to the researchers, the technology is scalable to higher power levels and can be integrated into different platforms, such as unmanned aerial vehicles, to support the long-term needs of the POWER program. For the tests, both the transmitter and receiver were on the ground, which required the beam to go through the thickest part of the atmosphere. The POWER Receiver Array Demo (PRAD) set the records for power and distance for optical power beaming; the graphic shows how it compares to previous notable efforts. Courtesy of DARPA. “It’s a lot easier to send a power beam directly up or down relative to the ground because there is so much less atmosphere to fight through,” said POWER program manager Paul Jaffe. “For PRAD, we wanted to test under the maximum impact of atmospheric effects.” While efficiency wasn’t the focus of this demonstration, the team measured more than 20% efficiency from the optical power out of the laser to the electrical power out of the receiver at shorter distances. Because the goal of the effort was to rapidly validate the capability of a new design to massively extend potential distance, trade-offs were made to accelerate the design and build of the test receiver. The receiver was completed in about three months. With the PRAD testing completed, the POWER program has significantly reduced risk for a key element of the realization of long-distance power beaming. The program is now moving forward to demonstrate the benefits of integrated relays and vertical power transmission and is seeking potential partners to help complete the project’s second phase.