Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

Light The Moon?

Eidetical

Active member
Joined
May 14, 2022
Messages
199
Points
43
In 1962, a group of MIT scientists hit the moon with a pulsed ruby laser beam and detected its return (with a photomultiplier tube) for the first time. The Raytheon model LHM-1 they used is seen below. They used large telescopes on both outbound and inbound beams. Rangefinding to the moon was sooo important, they lugged that big heavy retroreflector array up on the first mission to land to get a much stronger signal.

I believe the human eye can detect a single photon of green light. I believe the few joules of output that Raytheon laser had can easily be topped by today's (probably 30 year old surplus) frequency doubled Nd:YAG lasers that can run faster than a few pulses per minute. I'd imagine that large telescope access is easier these days.

I wonder if it would be possible to actually see a green spot on the moon, looking through a big telescope. Yeah, I know, "Paint the Moon" garbage and all that from years ago, but I still gotta wonder. Keep that big scary laser spitting out those monster green q-switched pulses, modern tracking, adaptive optics, maybe multiple lasers hitting the same spot. I think I'd see me some green!

Anyway, here's the laser and the guys, and a pic of it without the cover next to the smaller model LH-3:

Raytheon LHM-1 .jpg

Raytheon LHM-1 Guts.jpg
 





Joined
Jul 10, 2015
Messages
9,877
Points
113
It sounds like a nice idea, but the spot is so spread out by the time it hits the moon that you can't see it, even if you had a million watt DPSS and a big beam expander, we are still talking about 1/4 million miles, your spot would cover a significant portion of the moon making it impossible to see.

The reflectors on the moon do reflect laser light back, but it takes amplifiers just to detect it on Earth because what comes back is extremely faint.

apollo_reflector.jpg



p.s Have you seen the GuideStar lasers used to excite sodium atoms @ 90 km for adjusting adaptive optics ? https://en.wikipedia.org/wiki/Laser_guide_star
eso1613a.jpg
 
Last edited:

Unown (WILD)

Well-known member
Staff member
LPF Site Supporter
Joined
Sep 4, 2020
Messages
1,439
Points
113
Wow imagine having that in a portable
 
Joined
Jul 10, 2015
Messages
9,877
Points
113
I would love to see the materials science advance to where we could buy single mode laser diodes like the Sharp 488 and Osram 520 only able to output dozens of watts with the same beam specs, alas the efficiency would have to be near 100%
 

Eidetical

Active member
Joined
May 14, 2022
Messages
199
Points
43
I believe the spot would only cover about a mile diameter on the moon. This calculation needs more than hand-waving. They need photomultipliers to make measurements, but there's still more than a few photons hitting the eyepiece there. I read they use pulsed green at 50Hz to make those measurements now, or maybe an IR wavelength. The telescopes they use are hobbyist size now.
 
Last edited:
Joined
Jul 10, 2015
Messages
9,877
Points
113
Even a 1 mile dia. spot on the moon would be impossible to see unless....well how many watts would it take ?

I look at my lasers spot at about 500 meters through a spotting scope ( no pun intended ) and both direct and dpss spots are no longer round/rectangular, they are a splotch of sorts, still if you could produce a 1 mile wide splotch/spot on the moon a 1/4 million miles away, how bright would it need to be to see it from Earth at night if shown on the Earth facing dark part of even a " new " moon ?

What would it take to do moon advertising ? Is it even possible ?

image14.png
 
Last edited:




Top