25 dollars via PP to who ever best answers this optical problem.

[Laser57]

As I understand this, to keep the line as thin as possible for as long a distance away as possible, you just start out with a low divergence collimated beam which is turned into a line using a cylindrical lens (or a laser line generator lens), that the low divergence properties of the collimated beam are not affected by the lens in the perpendicular plane opposite of the line and will be the same divergence in that plane.

In simple terms, what I want is the thickness of the line to remain as thin as possible for as far as possible, or to have as low divergence as I can get in regard to the thickness of the line as it travels forward. This will allow the line to remain as bright as possible to a distant observer, that's what I'm after, I want to use a line because you can't miss with one, just sweep it up and down in the direction you want to be seen and it will cross someones vision. I have a small rescue laser which is made for that purpose, but it just uses a simple cylinder lens and the thickness of the line gets pretty darn wide at a distance, I want to make one which keeps as much power as possible in the thin line so it is brighter (I think I beat that horse explaining the project far too much, but wanted to make sure I'm understood).

What do you think about this idea, I produce a thin line by using a laser line generator and then shoot that line into a cylindrical concave lens so that the line is expanded to make it thicker, isn't this the same as using a beam expander to reduce the divergence even further?

Thank you for your help guys, I guess I won't have to wait two weeks

[Eidetic]

If that's your application, you'll have to upcollimate (to, say, 10mm like the example Steve gave above). Easy and cheap to do, and shouldn't be a problem for a rescue laser. Any line generation technique will work, but you'll want very little spread in that direction compared to that used for making a line for cutting or construction.

[Laser57]

I suppose I could take the raw uncollimated output from a laser diode and shoot it into a long one axis plano-convex cylindrical lens to turn it into a line, but with the distance between the laser diode and the lens, the beam would expand quite a bit before collimation into a line, producing the same effect as a two lens beam expander, except to produce a low divergence line?

[White-Light]

As I understand this, to keep the line as thin as possible for as long a distance away as possible, you just start out with a low divergence collimated beam which is turned into a line using a cylindrical lens (or a laser line generator lens), that the low divergence properties of the collimated beam are not affected by the lens in the perpendicular plane opposite of the line and will be the same divergence in that plane.

In simple terms, what I want is the thickness of the line to remain as thin as possible for as far as possible, or to have as low divergence as I can get in regard to the thickness of the line as it travels forward. This will allow the line to remain as bright as possible to a distant observer, that's what I'm after, I want to use a line because you can't miss with one, just sweep it up and down in the direction you want to be seen and it will cross someones vision. I have a small rescue laser which is made for that purpose, but it just uses a simple cylinder lens and the thickness of the line gets pretty darn wide at a distance, I want to make one which keeps as much power as possible in the thin line so it is brighter (I think I beat that horse explaining the project far too much, but wanted to make sure I'm understood).

What do you think about this idea, I produce a thin line by using a laser line generator and then shoot that line into a cylindrical concave lens so that the line is expanded to make it thicker, isn't this the same as using a beam expander to reduce the divergence even further?

Thank you for your help guys, I guess I won't have to wait two weeks

Is this for an emergency signal then?

If so it may help to know if it has to be hand held like a torch or if it can be a small boxed unit attached to and powered from a snow mobile. The size and power availability and even some idea of cost will help people to advise you on what's available. Eg one of the best lasers for beam specs is OPSL but they cost a fortune and I doubt they could be made hand held. Gas lasers would probably be too fragile etc etc.

[buffo]

to keep the line as thin as possible for as long a distance away as possible, you just start out with a low divergence collimated beam which is turned into a line using a cylindrical lens (or a laser line generator lens), that the low divergence properties of the collimated beam are not affected by the lens in the perpendicular plane opposite of the line and will be the same divergence in that plane.

Correct. The cylindrical lens will not affect the vertical axis at all, so the divergence will stay the same.

In simple terms, what I want is the thickness of the line to remain as thin as possible for as far as possible, or to have as low divergence as I can get in regard to the thickness of the line as it travels forward. This will allow the line to remain as bright as possible to a distant observer, that's what I'm after

You have a conceptual error here: The thickness of the line is NOT the limiting factor in how bright the line will appear to a distant observer.

The length of the line will affect the brightness a whole lot more. You are spreading the power of the output beam out over a very wide area, and the trivial change in power due to the vertical thickness of the beam is insignificant compared to the logarithmic reduction in power due to the length of the line. (The average power at any point along the line will drop off rapidly as the distance increases.)

Remember, perceived brightness is proportional to intensity, and intensity is power per unit area. So as the area goes up, the intensity (and thus the perceived brightness) goes down. So which factor increases the area the most? The vertical divergence, or the length of the horizontal line?

One way you can help minimize this power reduction is to use a spinning polygonal mirror instead of a line generating optic like a cylindrical lens or a diffraction grating. That way when the beam sweeps past an observer, it will have the full strength of the beam, albeit for a brief period. So long as the mirror is spinning at a speed fast enough that the line appears solid to the eye (thanks to the persistence of vision), this will work far better than a static line-generating optic.

If I produce a thin line by using a laser line generator and then shoot that line into a cylindrical concave lens so that the line is expanded to make it thicker, isn't this the same as using a beam expander to reduce the divergence even further?

If you want to up-collimate, you need a lens pair. One to expand the beam, and another to bring it back to parallel again. The first lens will be positive, the second one negative. However, you are correct in that you can expand just the vertical axis using a pair of cylindrical lenses mounted after the line-generating optic, if you want, and the results will be similar to using a beam-expander mounted before the line-generating optic.

I suppose I could take the raw uncollimated output from a laser diode and shoot it into a long one axis plano-convex cylindrical lens to turn it into a line, but with the distance between the laser diode and the lens, the beam would expand quite a bit before collimation into a line, producing the same effect as a two lens beam expander, except to produce a low divergence line?

Not quite. You want to have some sort of initial collimation on the beam as soon it exits the diode. The closer you get that primary lens to the emitter, the better. After that, if you want to up-collimate the resulting beam, you have lots of space to do it.

In my opinion, the BEST way to do this would be to start with a standard collimated source (use a single-mode diode with a small emitter and a GOOD primary collimating lens). Then up-collimate the entire beam (as suggested above). The beam would pass through a diverging lens first (double-concave) and then through a focusing lens (double convex) to bring the beam back to as close to parallel as possible.

After that, you would use either a line diffraction grating or a cylindrical lens to create the line. The vertical axis of the beam would remain untouched, and since you up-collimated it already you should get very low divergence numbers. And as mentioned above, if brightness is your primary concern, then ditch the idea of using gratings or cylindrical lenses and instead use a multi-sided spinning mirror to sweep the beam and make the line.

Adam

[mixedgas]

Having observed lasers from aircraft, you really do not want much of a spread. Unless someone has already localized you via other means, they will be searching at an altitude that is a tradeoff between: A height where the aircraft is efficient for long duration, A height known to them to have a wide visual field yet allow a human observer to be the most effective, and a height known to avoid obstructions in the area. That height gets lower if they know your rough position. You need a large, low divergence, beam to maximize slant range. Especially during daytime.


Far better to have a LARGE up-collimated beam and a small mirror to aid in a slight sweep or a less then 2.5' spread linear lens. Loosing optical power in a log pattern is not a good idea.


The human eye, especially the peripheral vision, homes in on blinking or motion. The most annoying blinking is from a half second period to a one and a half second period. At any distance, the laser is undergoing atmospheric scintillation which adds a natural blink or shimmer to the beam. The optical lever effect adds to the tremors in your hand, also causing a cyclic undulation at the detector. Which is one of the reasons pilots are so annoyed by a laser pointer misused. So no real need to blink the beam.

Laser rescue beacons are patented by an Alaskan company. http://www.greatlandlaser.com/ If you can improve upon their patent, you can market this.

Far, far better to have a EPIRB or a radio on 121.5 Mhz on land, or Marine 16 for water. 2-5 watt VHF radios are good for a roughly 10 mile sphere around you with a quarter wave or half wave antenna, when the RX is on a aircraft. Not so much range with a lame helical "rubber ducky" antenna. Every commercial flight and many bush pilots are monitoring Guard or local CTAF.

Xenon rescue strobes are HIGHLY effective. Small, and carrying a second battery is easy. Xenon works well because the eye physiology is annoyed by pulsed light with a high peak power. Especially in the 350 microsecond region where Xenon tubes run.

If I wanted a laser beacon, I'd also consider one of the Laser Genetics handhelds which are sort of designed for this. I'm not a fan of laser flashlights, a good 3 or 4 cell LED Maglight with flash mode would often be a better choice, as laser diodes eat batteries. The temperature compensated Green laser flashlight has a heater which burns even more energy when in use. Ideally you have a handheld laser, a flash, and a rescue mirror with a sighting hole in it.. The flash works when you have hypothermia, too.

You can thank my Scoutmaster, who was a retired Army Colonel, and the Assistant Scoutmaster, Ex Special Forces warrant officer (Comms) , for drilling all this into me. Except for the laser stuff..

One of these days Charlie and Harry, if you can see this from Heaven, I'll forgive you for making us do the survival course "Your Way" in winter, and again in summer.

Steve

[buffo]

Far, far better to have a EPIRB or a radio on 121.5 Mhz on land, or Marine 16 for water.

This! A thousand times, this!

EPIRB's will save your ass if you are lost and injured in the back-country. And you are an absolute fool if you venture off-shore (beyond LOS comm range) in a boat without one.

Adam

[Laser57]

Thank you for all of your insight, I have a lot of thoughts about your suggestions, I take your point about the mirror being the better way to go and I agree, I need a spinning mirror to do this for maximum light at a distance. I did consider that idea earlier, but I am not sure what to buy, I see mirrors made for projectors and other spinning hex mirrors for scanners and considered all of them, but the one thing which holds me off is I don't know how many degrees of scan I can get out of a scanning mirror like that, or whether I should use a projector mirror. I've never been involved with projectors, only laser pointers, so I don't know what to buy and started looking at cylindrical lenses instead. Can you point me towards some candidate vibrating or spinning mirrors small enough to incorporate into a very large pointer? Although I am basing this off of small rescue lasers, I don't intend on taking this unit with me while flying, or traveling, it's just a hobby for me and it can weigh 10 pounds for all I care. The last beacon I worked on weighed over a hundred pounds, so even at ten pounds this would be a compact unit

http://imageevent.com/qdf_files/tech...ndlaserproject

I can have a host machined for it, I don't expect any of this to be cheap and willing to pay what it takes to build this. My interest in this is my only hobby right now, I want to build my own instead of buy one. I already have lots of single mode laser diodes I bought for this, I wanted to combine the power of 30 of them into a line by paralleling their outputs into a plano convex cylindrical lens, that was my idea of increasing the average power in the line, due to how much drop off in power there would be from the energy being spread out like that.

I have another question regarding using a lens far beyond a laser diode to allow the beam from the diode to spread out before collimation, I see you are telling me it is better to collimate close to the diode and then up collimate afterwards, but I don't see why, the expansion of the light from the diode is still expansion which I thought would reduce the divergence. I had a laser guru telling me that would work and reduce divergence at the same time, perhaps I received bad advice on that point. I have some lasers which are built that way to make fat beams, just one lens a few inches from the laser diode and thought the divergence would be less that way, but I never measured to confirm it.

[mixedgas]

Yes, you can collimate with a single element lens downstream, but will suffer diffraction loss and may not get optimal divergence with a single element, uncorrected lens. Collimating after scanning is optical suicide. That requires a "predistortion" lens before the scanner and optical modeling software to design. It also greatly restricts your scan angle for a given lens diameter. Which is why the wide field lenses for laser shows are so expensive, it is a non-trivial design task.

Steve

[Laser57]

OK, thank you again. Please check my understanding; best to collimate first close to the diode and then upcollimate (expand) the beam for lowest divergence.

In one version or idea of doing this, I was also planning on using a small G2 lens with my DTR single mode laser diodes all pointing towards one long cylindrical plano-convex lens, but each laser output defocused just enough to allow the beam to expand to fit within the two inch height of the cylinder lens. The plan was this would, in effect, function the same as expanding the output of the laser diode without the use of an additional concave cylinder lens.

This is a very rough drawing of a pointer I had planned on having machined:



I had the photo upside down so reattached it with the correct orientation... The slots in each section were to allow individual focus of each row, since there would be an off-set from the center of the lens due to the thickness of the glass being thinner both above and below center. Not sure this would work to produce a fine line for each of the three rows or not. I wanted three lines, one for each color of R,G,B.

I'm still interested in this design, if it will work properly using the lens that way with three rows of diodes, but at this point, perhaps i should use a rotating mirror to increase the visible power using one high power laser diode instead of combining multiple single mode diodes into a line, but then my divergence is higher....

I will have my light saber yet, just need to work out the wrinkles. Has anyone seen a really cool miniature galvo I could use to scan the output of a laser diode suitable for mounting in a big pointer housing? Maybe there is a way to have multiple laser diodes all reflect off of the same galvo mirror, ideas welcome I already have all of the diodes as well as drivers to put this together with.