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Hello all! First Timer Here. Need Your Help!

Campy

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Hello to all the good people at the forum. I have been reading many posts over the past five or six months and have enjoyed the conversation. I have been observing because we have been planning on doing an experiment here in the next week or two but I have hit a major snag and now we are a bit stuck and could really use your assistance. So, tonight I signed up. Hope you can help.

Long story short... we are doing some Earth curvature experimentation. Let's leave that aside for now and see if we can get us where we need to be.

1. A while back we purchased a 1W Green Laser and tried conducting a 4 mile test across the ocean. The beam was between 12-15 feet in diameter at the 4 mile distance rendering the test useless.

2. We then purchased a 2W Blue Laser and a 3W Blue Laser. The 3W was from China and I bet the 2W is a better quality laser but tests have shown otherwise.

3. We tested the 2W laser at 3.26 miles and 3.44 miles and because the blue lasers output a rectangle instead of a circle, we got a beam of 8'x15' and 9'x19' respectively. These were not exact measurements but are probably within 2-3 feet. Realizing that we were going to need a much smaller beam, we purchased a 10x Beam Expander and that just arrived yesterday.

4. That brings me to the issue. First off, we have the expander and it has a male connector that measures 17mm. We have two lasers, unsure which is better for the experiment, the 3W has a female threaded hole that measures 12mm and the 2W measures at 11mm. These were measured using the lens inserts that came with each laser.

5. I went to Orchard Supply and could not find any adapter or connector that would allow a 17mm male to be transferred to a 12mm or 11mm female. So, that is my first question. I see many of you selling various parts and sinks and I wonder if by chance, anyone has or can make or can point me to where I can get an adapter to connect our expander to the lasers themselves. Also, is this a best practice or is it better or more feasible if I instead build a housing with fine threaded adjustment screws to hold the expander and allows the laser and the expander to be joined like that?

Now, I want to explain the test that we had planned on doing this next weekend, that can only be done if we figure out how we are going to get this to work and also I am looking for any input or advice as to what to expect for a beam divergence with the added focuser. Originally, the test was going to be done where as we would need a very small beam at the distance of 3.88 miles (distance of test) but we have changed the test a bit to eliminate the need of a level laser beam and housing.

Now what we have is a theodolite that will be used to measure the distance off the surface of water to where the beam passes a wooden post. So, we will have a wooden post next to the river, premarked at 6" intervals. We will use the theodolite and measure the distance from the surface of the river to the wooden post. Let's use 5 feet as an example. So, once we know the bottom of the post is 5 feet above the water line, we obviously know every spot on the post and its distnace from the water since we will have premarked it. We are doing this to 3 posts. One at about 20 feet distance from the laser, one at 1.94 miles and one at 3.88 miles. Due to terrain, each post may be slightly different so we said post 1 was 5 feet, we can pretend that the middle post is 5.5 feet and the far post is 6 feet just for this example. So, the plan is, once all three have been measured, is to shoot the laser from the starting point, having it pass close to each. The goal being to line up the laser such that it hits the first and last post at the same spot.

This is where the size of the beam at 3.88 miles comes into play. We need to be as accurate as possible and so my first question is, what size beam do you expect? Because what we are trying to do is to get the beam to pass post one and post three, at the same point. For example.... let's say we pass post one at 8 feet, then we want to get the laser to hit the post at the 3.88 mile mark at the same distance above the water line, in this case 8 feet. Once we are satisfied that both the first post and last post are being passed or hit at the 8 foot mark, then someone at the middle post at 1.94 miles will quickly see where the beam crosses the middle post. If the earth is curved as science and all educational teaching has taught, then the beam will cross the middle post at 5.25 feet instead of 8 feet. If it crosses at 8 feet, then we have an interesting result as this would show that over a span of 3.88 miles, there was not the observed drop that we have been taught must be present.

So, sorry so much for short huh. The biggest question... without getting into details about the curvature of earth is where can I get the adapters we need to attach the focuser and any other helpful hints... I am all ears... and eyes of course. Thanks for your time.

JC
 

Campy

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Alaskan

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That appears to be a Jetlasers PLE Pro along with their 10X expander, is that what you have? Is it 520 nm? At 1 watt, it must be. If you had purchased the 800 mw DPSS PLE Pro the divergence would be about half of what a 520 nm laser pointer can produce, for a given lens size.

If you know the divergence of the laser pointer you can can calculate the expected spot size using this online calculator: pseudonomen137's JScript Diameter Calculator

If you are starting out with 2.6 mRad, which might be about right for a 520 nm laser diode, and then put a 10X beam expander on it, the divergence should be close to 1/10. To use a beam expander you must make sure the input aperture diameter is large enough for the diameter of the beam going in, and that the output lens size is large enough to produce the desired amount of expansion without clipping.

For example, a 2 mm diameter beam from your laser pointer into a 10X beam expander needs a output collimation lens of more than 20 mm diameter. Some laser pointers produce such a large diameter output beam that some beam expanders can't be used, obviously 4 mm into a 10X beam expander with only a 25 mm output lens would cause the beam to be clipped, much of the power blocked. Although, in such a beam expander, you would probably have too small of an input aperture or diameter to get all of the power into it anyway, it would be blocked on the input for most designs.
 

Campy

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That appears to be a Jetlasers PLE Pro along with their 10X expander, is that what you have? Is it 520 nm? At 1 watt, it must be. If you had purchased the 800 mw DPSS PLE Pro the divergence would be about half of what a 520 nm laser pointer can produce, for a given lens size.
Those are just images I grabbed from the net. Do you want pictures of my two lasers and the expander? Also, the problem with doing any measurement as you have suggested is I can't connect them currently. I would think it isn't too safe to just hold them to each other but I don't know... you tell me. I can take images right now if that would help.
 

Campy

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Well, not sure anyone wanted them but here are some images of the lasers and focuser...


Thanks again for the assistance
 

lasersbee

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Welcome to the Forum...
Looks like an interesting project...
Enjoy your stay.

Jerry
 

Campy

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Welcome to the Forum...
Looks like an interesting project...
Enjoy your stay.

Jerry
Thanks Jerry... and 3DLaSeRBuiLDeR and ArcticDude as well. Nice to be here. Hope someone can help me get this experiment done! lol
 

lasersbee

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Thanks Jerry... and 3DLaSeRBuiLDeR and ArcticDude as well. Nice to be here. Hope someone can help me get this experiment done! lol
I know you are new here... but it is
frowned upon my the Forum community
to Double Post.
It is easy to edit or add to a Post by
using the [EDIT] button at the bottom
right of each of your Posts...

Jerry
 

Alaskan

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That beam expander is certainly a 10X Jetlasers, I'm bowing out from here, busy with other things but good luck with your project. Oh, the edit button is your friend, I use it A LOT, saves the double post.
 

Hap

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Welcome to LPF Campy! :yh: :beer:

-Alex
 
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