Spy satellites generally don't communicate directly with each other and never attend the same parties. Normally they play a game of Chinese whispers by using radio signals to transfer data down to a ground station on Earth, which then relays this data to the other satellite.
Optical terminals between satellites are considered to be faster and more secure, at least according to CACI International -- the company that developed the optical terminals for the space lasers.
The two satellites, named Able and Baker, were launched last summer by the U.S. Défense Advanced Research Projects Agency as part of its Blackjack project. DARPA wants to build a constellation of military small satellites in low Earth orbit.
The two satellites successfully pulled off the 40-minute laser communications experiment on April 14, during which time Able and Baker used CACI's CrossBeam free-space optical terminals. Infrared lasers transmit data by encoding the message into an optical signal, which is then carried to a receiver.
The experiment, known as Mandrake 2, was funded by the Space Development Agency (SDA) and the Air Force Research Laboratory. Mandrake 2 launched on June 30, 2021 as an early risk-reduction flight for DARPA's Blackjack constellation project.
The Blackjack constellation aims to deploy an initial batch of 20 small satellites in low Earth orbit, which will connect with each other to form a mesh network in space.
The agency is seeking to create a full constellation that would include somewhere between 300 and 500 satellites in low Earth orbit. The satellites are being developed by Lockheed Martin, Northrop Grumman, and York Space.