35 mile laser shoot

Last Saturday night at about 10pm I was at Warm Springs Oregon. That is an Indian Res. My 2 grown children are 1/2 Warm Springs Indian. We were at a house on a hill overlooking a valley, more of a bowl 4miles in diameter.To the southwest is Mt.Jefferson about 35 miles away. It was a clear night with little wind and no clouds or particulates in the air. Hitting the sides of the valley "bowl" was child's play for my RPL-450 with a 3X beam expander. So we started pointing towards Mr.Jefferson with its white snowy slopes. All four of us were sure we could see the light scattering when it hit the snow but weren't sure. So we got out the Orion 6" reflector telescope and pointed it at the mountain. Sure enough that laser light was going 35miles reflecting off the snow and enough of it was left to see the return image in the telescope. That was some exciting stuff.
I know there may be some who will doubt you could hit the mountain at 35 miles but all four of us saw the same thing. I will get a decent camera soon and make photos of this in the near future.

Only 35 Miles ??? Some folks using a telescope have found the reflectors on the moon. Still it's fun to see the beam at that distance.
Always look out for aircraft.

Mike

On the moon?

I've seen pics of the gear used for the lunar range finding experiments - seems to entail a lot more than a powerful green and a simple telescope.

As for seeing the reflection at 35 miles: that seems entirely feasible with some binoculars or a telescope, as long as its dark.

Benm said:

On the moon?

I've seen pics of the gear used for the lunar range finding experiments - seems to entail a lot more than a powerful green and a simple telescope.

As for seeing the reflection at 35 miles: that seems entirely feasible with some binoculars or a telescope, as long as its dark.

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Hi Benm,
I would have to agree with you, it takes orders of magnitudes of both laser power and light gathering (telescope) than any hobbyist or amateur is going to have on hand.

I just visited the McDonald observatory lunar ranging system website.
The specs for the laser is 1500mj which is 1.5 joules of energy, it supplies this energy in a 200 picosecond pulse. Converting this amount of energy over this short time period your looking at 750GW, that Gigawatts or 7500000000 Watts with a beam diameter of 7mm and a divergence of 0.075urad (micro radians).
On the receiving end they use a 30 inch reflector coupled to very sensitive electronic sensors and when they send this 200 picosecond pulse of 750GW, they only get back a few photons of the light that was transmitted.

That will be interesting to see. A 10X beam expander should make it even easier to see the the spot with the naked eye

They went there on Mythbusters on the Moon landing Myth eppisode.

why don't i see the 450mw laser on the opto site? the max il 425.

I have some A4 sized fresnell lenses on their way here - they could be part of a very nice beam expander if somehow properly set up. The good thing about large beam expanders is that ridicilously large amounts of power are still essentially eye safe - 400 mW on a 20x20 cm would still limit eye exposure to under 1 mW (each, and in this case you might hit both at the same time ).

Regarding the moon bouncing, the returning light was measured in individual photons. That little light would be impossible to detect by eye. You'd definitely need a telescope, like Mike said, but even then, I think you'd have a difficult time seeing the reflection..

Wow, that is quite impressive. Counting the reflection, the total distance is actually 70 miles! What's even more impressive is that a lot of light had probably been scattered when it hit the snow.

I'm guessing if you were to look into the beam directly, you would be able to see it several hundred miles way in a low-light, low-disturbance environment (such as a desert).

I got up at around 2am that night(day)and pointed the beam around the edges of the valley "bowl" and got a 100 coyote chorus. That too was impressive.
When I talked with Jack about upgrading my RPL-225 he said he had three 450s' that he hadn't put up on the web site yet. He gave me the "homey hookup" supposedly. It is indeed a 450. I tend to agree with Jack that you get more "bang for your buck" with a 3X than a 10X beam expander. I have both.

ixfd64 said:

I'm guessing if you were to look into the beam directly, you would be able to see it several hundred miles way in a low-light, low-disturbance environment (such as a desert).

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You could, but you would need to get up very high to have a horizon that far away. If you were to construct 2 towers, each 500 feet tall, you could shine and observe a beam between them over 200 miles or so.

Also, you should probably define 'dark'. The human eye is capable of registering a single photon entering it if adapted to complete darkness for a long time. Under starlight, and especially moonlight, this would already be different. Considering urban background lighting, it's a different picture altogheter.

Hey that was a great story. I'm guessing that a 300mw greenie would be blindingly bright all the way to the horizon ~10-14 miles, looking straight into the beam.

usakicksass said:

It is indeed a 450. I tend to agree with Jack that you get more "bang for your buck" with a 3X than a 10X beam expander. I have both.

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How so ?

The 3X gives all the focus you need for playing around. The 10X does the same thing, barely noticeable in comparison, but at twice the price.

usakicksass said:

The 3X gives all the focus you need for playing around. The 10X does the same thing, barely noticeable in comparison, but at twice the price.

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I thought price was what you were refering to.
However performance wise a 10x expander will put more energy into a given area do to the smaller beam divergence; which would translate into a brighter spot in the far field. And if it's distance you want then lowering the beam divergence is the goal. However very low divergences can be counter productive by spreading a beam to wide from the start will result in a given area in the far field with a lower over all radiance making it difficult to see with the naked eye. I know this from practical experience.