CE5
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It would be swell, if more interest could be generated here on LPF concerning FSO-free space optical, communication applications.
What I learned in a nut shell:
You don't need high power if you can get a low divergence laser diode which has a tiny emitter and expand it, they can be only a couple hundred milliwatts if single mode and produce a beam which can stay in a relatively tight beam to be viewed as the brightest spot of light coming from the earth (if you are away from other light sources so it can stand out). However, if the beam is uber tight, it is also uber difficult to put on a target too, perhaps too difficult.
Here's what I'd do, I'd mount and align a low divergence IR laser diode which has been expanded to a few inches diameter directly on a telescope, mount it right on top of the telescope so you can spot properly. Alignment is going to be extremely tedious and might not work out very well for extremely long distances over a couple hundred miles, but I haven't researched that aspect well enough to give advice on it.
You can also use a high power source (which I just said isn't necessary) and get the same low divergence of a single mode low power diode by expanding the beam to a very wide beam. Doing so can produce a beam just as tight as an extremely low divergence diode, but with more power. However, still difficult to put the spot on something because the output won't be very wide a long distance away.
If you want to attract something out there, might be better to use a 1064 nm YAG laser, expand the output as wide as you can and then collimate it. After that put a large number of optical line rods in front of the collimated beam, just stack them to cover the entire output. Now you will have most of the power converted into several laser lines and can sweep a very large area without missing your target, that is, if you want to make a beacon. The power which will land on the target will be extremely reduced, but if you are using a YAG laser with several million watts of peak power all packed into nanosecond pulses, I think it might still show up at the distant end as a very bright source, even if 100 or more miles away.
What I don't know is how safe this is, it might not be safe, might not be at all advisable. If you hit someone close by, especially since it would be a wide line, it could blind someone. So, I don't advise doing something like that until you have had a professional run the numbers to give you a good idea how hazardous the beam could be to someone close by, or within a mile or more distant etc. Off the top of my head, I'd guess this is very hazardous as well as illegal. Maybe this isn't a reasonable project to build, maybe too dangerous, I just don't know. However this might produce a flash of IR light which can be viewed from extreme distances and then you don't have the trouble of trying to target something with a very tight beam which is nearly impossible to put on something and keep it on it if they are moving, or even if stationary, when very far away.
Maybe better not to go the YAG route, you could however use the same concept with a single mode laser diode which has much lower power and constant, instead of a short pulse. Just expand the output as big as you can get it and put a bunch of line producing rod lenses in front. You could make a fairly small hand held laser pointer to do this with, but I don't know I would build something like this in the visible spectrum. Expanding the beam will produce a very low divergence output, putting a line lens in front will produce a line which expands very little in thickness as it travels forward and you would be certain to be flashing a lot of aircraft out there which is illegal. Would the line be weak enough it doesn't matter? If it is that weak, then it isn't effective for your use either, but if you can get enough power at IR into a line being produced from a uber low divergence beam, it might work, but still hazardous close up, I am sure.
Some membeers will certainly caution you against doing this, I am too, but wanted to share some ideas, might be work arounds so it can be done safely, but the beam will need to be expanded to a huge diameter to reduce the power density to be safer.
It would be swell, if more interest could be generated here on LPF concerning FSO-free space optical, communication applications.
I've done something similar. I've attached my laser to a spotting scope. I had to come up with a mount to center the beam incrementally.What I learned in a nut shell:
You don't need high power if you can get a low divergence laser diode which has a tiny emitter and expand it, they can be only a couple hundred milliwatts if single mode and produce a beam which can stay in a relatively tight beam to be viewed as the brightest spot of light coming from the earth (if you are away from other light sources so it can stand out). However, if the beam is uber tight, it is also uber difficult to put on a target too, perhaps too difficult.
Here's what I'd do, I'd mount and align a low divergence IR laser diode which has been expanded to a few inches diameter directly on a telescope, mount it right on top of the telescope so you can spot properly. Alignment is going to be extremely tedious and might not work out very well for extremely long distances over a couple hundred miles, but I haven't researched that aspect well enough to give advice on it.
You can also use a high power source (which I just said isn't necessary) and get the same low divergence of a single mode low power diode by expanding the beam to a very wide beam. Doing so can produce a beam just as tight as an extremely low divergence diode, but with more power. However, still difficult to put the spot on something because the output won't be very wide a long distance away.
If you want to attract something out there, might be better to use a 1064 nm YAG laser, expand the output as wide as you can and then collimate it. After that put a large number of optical line rods in front of the collimated beam, just stack them to cover the entire output. Now you will have most of the power converted into several laser lines and can sweep a very large area without missing your target, that is, if you want to make a beacon. The power which will land on the target will be extremely reduced, but if you are using a YAG laser with several million watts of peak power all packed into nanosecond pulses, I think it might still show up at the distant end as a very bright source, even if 100 or more miles away.
What I don't know is how safe this is, it might not be safe, might not be at all advisable. If you hit someone close by, especially since it would be a wide line, it could blind someone. So, I don't advise doing something like that until you have had a professional run the numbers to give you a good idea how hazardous the beam could be to someone close by, or within a mile or more distant etc. Off the top of my head, I'd guess this is very hazardous as well as illegal. Maybe this isn't a reasonable project to build, maybe too dangerous, I just don't know. However this might produce a flash of IR light which can be viewed from extreme distances and then you don't have the trouble of trying to target something with a very tight beam which is nearly impossible to put on something and keep it on it if they are moving, or even if stationary, when very far away.
Maybe better not to go the YAG route, you could however use the same concept with a single mode laser diode which has much lower power and constant, instead of a short pulse. Just expand the output as big as you can get it and put a bunch of line producing rod lenses in front. You could make a fairly small hand held laser pointer to do this with, but I don't know I would build something like this in the visible spectrum. Expanding the beam will produce a very low divergence output, putting a line lens in front will produce a line which expands very little in thickness as it travels forward and you would be certain to be flashing a lot of aircraft out there which is illegal. Would the line be weak enough it doesn't matter? If it is that weak, then it isn't effective for your use either, but if you can get enough power at IR into a line being produced from a uber low divergence beam, it might work, but still hazardous close up, I am sure.
Some membeers will certainly caution you against doing this, I am too, but wanted to share some ideas, might be work arounds so it can be done safely, but the beam will need to be expanded to a huge diameter to reduce the power density to be safer.
Really, the best option you are going to have is to get a DPSS 532 then. It won't be as bright as a 520 at night, but the divergence of a 532 will more then make up for it on distance vs the 520.