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Interplanetary precision laser could put a red dot on the red planet

A new “interplanetary precision laser” is being developed which increases the range of lasers so they theoretically could reach Mars and beyond.


Current laser technology allows for us to shine our lights at some pretty far away places. Lasers can today reach the moon, and have been pointed at it for various reasons, including accurate measurement of how far away it is. Conventional precision laser technology uses something called “passive laser ranging”. Laser light being emitted using this technology deteriorates at a rate of R^-4, where R is the distance the light has traveled.

A newly developed technology, “active laser ranging”, features signal deterioration of only R^-2, making it many, many times farther reaching. The system also features sub-milimeter accuracy, meaning it will be easier to point it at very distant targets. The scientists responsible for the discovery, Yijiang Chen, Kevin M. Birnbaum, and Hamid Hemmati from the University of California, have published a paper on the laser system in Applied Physics Letters.

“In principle, this approach could be scaled up to any interplanetary distance by increasing the size of the telescopes,” said Birnbaum in an interview with Phys.org, “We calculated that ranging from Earth to Mars or Jupiter should be achievable with quite modest telescopes of 1 m in diameter on Earth and 15 cm on the spacecraft.”

The old laser technology used a reflector, such as the mirrors astronauts have left on the moon, to bounce the laser signal back to Earth where it can be received and the travel time measured. The new active technology has a receiver and transceiver at each end. It actually has two laser-beams flying through space; one going to the target, and an entirely different one going back

Diagram of how the active laser ranging system works
Birnbaum explains further: “Compared to current optical technologies, the key is that we use an active transceiver. Currently, optical ranging is done by bouncing light off of a passive target, a reflector. This is very effective for ranges up to the Earth-Moon distance, but it is simply not reasonable for interplanetary distances because the planets are thousands of times farther than the Moon. The amount of light falls as 1/R4, so the signal would get trillions of times weaker if you tried to use the same passive system to measure the range of the planets. We use active transceivers with lasers at both ends, so each end can see a much brighter signal.”

What makes the new active system particularly useful is that it can be used with modern lasers and don’t require any particularly powerful devices to increase the range: “Commercially available lasers have enough pulse energy, and the light intensity as it leaves the transmitter can be low enough that it is even eye-safe. The key is to have a very sensitive receiver and a method to pick out the ‘signal’ photons from all the background light.”

Of course, the biggest challenge of sending a laser to Mars, as one can imagine, is that the receiver/transceiver actually has to be placed there. While robotic rovers could probably get the job done, it still involves a trip to the red planet, and obviously, there are certain environments where the technology isn’t feasible; but then again, you could say the same for passive ranging.

Via Phys.org

David F.
A grad student in experimental physics, David is fascinated by science, space and technology. When not buried in lecture books, he enjoys movies, gaming and mountainbiking

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