From the web site of the above video.
Photonic propulsion uses photon pressure for propelling spacecraft, does not need conventional rocket propellant and can thus achieve fractions of the light speed. However, traditional photonic propulsion is highly inefficient and impractical. Photonic Laser Thruster (PLT) increases photonic propulsion efficiency by more than 1,000 times by recycling photons between two space platforms. In this way, PLT enables innovative propellant-free spacecraft maneuvers and propulsion that are beyond the reach of the traditional rockets and thrusters. Therefore, PLT is projected to potentially revolutionize space endeavors from satellite maneuvers to human space travel. In the present demonstrations, a 0.5 kW laser platform was used for PLT to deliver 3.3-mN photon thrust to a CubeSat, which translates into a 500 kW intracavity laser beam. The 500 kW intracavity laser power was confirmed in two independent ways: one with the use of a radiation pressure meter and another optically by measuring the leaked laser power through the mirror on the satellite. The kinetics of the satellite agrees with the thrust estimated from the laser power.