BBC News: Space probe breaks laser record.
A spacecraft has sent a laser signal to Earth from 24 million km (15 million miles) away in interplanetary space. The Messenger probe exchanged laser signals with a US ground station partway through its journey to the planet Mercury. Messenger blasted off in 2004 on a mission to map the surface of the nearest planet to the Sun. After arriving in 2011, the probe will orbit Mercury for a year to explore its atmosphere, composition and structure. The US space agency (Nasa) craft is equipped with a laser altimeter that will map the topography of Mercury by timing the return of laser pulses fired at the planet. The instrument and the ground station in Maryland transmitted laser pulses back and forth in a test of the payload carried out in May.
Light Amplification by Stimulated Emission of Radiation, laser. White light is made up of many different wavelengths of light, lasers have just one, which makes them great for precision measurements. The laser laboratory at Surrey University had plenty of red (694nm) ruby lasers, and one green (532 nm) argon laser. Undergraduates weren't allowed to use the full beam of the green because it was a six watt laser, over a thousand times more powerful than the milliwatt reds you can buy as pointers. The green laser beam was piped around the room with mirrors and each work station could use a portion of the beam. Our experiments had to be enclosed in a box before you could open the slot to let the beam in. I remember doing interferometry experiments with the green laser, and making holograms with the reds.
The laser lab was an entirely black room, walls, ceiling, door, floor, black curtains enclosing each work station, and no windows. You would come out at lunchtime like a mole blinking in the daylight, and go back in until it was getting dark outside. One full day a week was spent in the labs for the first two years of my degree, with at least a month in the laser lab on various experiments. Bumped into Hubby once, after a morning in the laser lab. He was visiting a friend on campus months before we started dating. Rubbing my eyes, couldn't see where I was going, and bump! Fond memories.