Need help with PCX beam expander question, what is the required surface accuracy?

[Laser57]

OK, I've googled for a couple of hours, tried to think out of the box, contacted Edmund Optics to ask and still finding myself unable to find the info. Can someone help me please?

The project:

I'm hoping photographic PCX condenser lenses can be used for the collimation lens in a large laser pointer beam expander, I can easily find 150mm and larger diameter lenses made for photography darkroom use but what I can't find are specifications to tell me how accurate they are for lambda in the middle of the visible spectrum, or what the lambda surface accuracy is for Edmund Optic PCX lenses made for photographic use, not even in chat when I contacted them that way to ask, they just don't publish the information. Can anyone tell me what the typical surface accuracy might be for common photographic condenser lenses and just as importantly, what the minimum surface accuracy the collimating lens of a beam expander should be? I don't need the BE for holography or anything like that, just for a home made beam expander but what I need is low divergence and looking at 150mm/6 inch or larger diameter plano-convex condenser lenses. If higher than 4 lambda surface accuracy is needed for decent divergence, I don't think I can use one of those lenses, but if 4 lambda is good enough, that would be great news for me as I can't afford large PCX lenses with much higher than that. I'm making an assumption these lenses are at least 4 lambda, but the reality is, I can't even confirm that! But I do know, 8 lambda and higher for large lenses becomes extremely expensive, forget 20 lambda, not within my budget.

I know very little about optics, perhaps my assumption a surface accuracy of 4 lambda or worse will affect the divergence isn't exactly right, maybe the divergence will still be unaffected, but there will be distortion. If so, I don't care so much about that, I just want low divergence, the power inside the spot doesn't have to be evenly distributed. I found some very large PCX lenses on aliexpress but their lambda is 2, or what I believe to be a surface accuracy of 1/2 wavelength, if I understand the term correctly. Does anyone know if 2 lambda can be used as a beam expander lens if I don't care about distortion within the spot itself and only low divergence?

Your help, opinion or direction of where to find the info much appreciated

Thank you

Chris H.

[Laser57]

Found some of it, but only after asking here, arrrggg: https://www.newport.com/optical-surfaces

Figure Cost Applications
λ/2 Low Used where wavefront distortion is not as important as cost
λ/4 Moderate Excellent for most general laser and imaging applications where low wavefront performance must be balanced with cost
λ/8 High For laser and imaging applications requiring low wavefront distortion, especially in systems with multiple elements

* Unless otherwise stated, surface irregularity for Newport lenses is peak-to-valley, per surface.

If anyone has more to add or suggest, please do. I still have't found the typical lambda for photographic condenser lenses.

[Laser57]

Can anyone point me in the direction of someone who does laser optics consulting?

[planters]

You probably do not want to pay for formal optical consulting for a laser pointer project.

Wave front is a bit more complicated than a simple wave/x. The nature of the error matters. For example, a turned edge at the periphery of the lens will lower the wave front spec, but might be completely bypassed by limiting the diameter of the beam. Also, many specifications will be waves of error/cm across the lens, so a supposedly modest, 2 wave, 5cm diameter lens will be 1/25 wave for a 1mm beam passing through it.

As a rough guide, amateur telescope mirrors with a diameter of 100-200mm and a commercial specification of 1/8 wave are considered excellent and will produce nearly diffraction limited performance. A mirror's surface needs to be held to twice the accuracy of a refractive lens for the same performance (they are easier to make thank goodness). So, you are probably on safe ground at 1/4 wave. Assuming you are using a laser diode as your source then you probably can relax this standard significantly because these lasers are pretty poor optically.

Remember, these big cheap lenses are often uncoated and can waste up to 10% of the light per lens.

[kecked]

What are you making this for? It sound a lot like a device to paint a target. Given your location and this description I'm not really inclined to help you take down a helicopter. Enlighten me.

[planters]

Are we still in Afghanistan? If so, what for? But, if we are then I agree with Kecked, there is no guarantee that you are on our side and I am.

I understand that if your intentions were nefarious you would not be likely to volunteer such a location or expose your plans so openly; not...likely.

So, how about some details and some background?

[Laser57]

Yes, I am still in Afghanistan but what I do here is RF telecommunications, I can't play with lasers in a war zone, it would only attract attention and get me thrown off base, or shot at. This is for a future project once I am back home, from what I just read, I should have at least 4 lambda surface accuracy when using a laser diode so the lens doesn't reduce performance. What I like to do is put spots on high clouds and see how high I can see the spot, one thing I would find interesting is if I expanded the beam from a low power single mode laser diode to such a wide beam-width the divergence is cut down to a very small number, but being expanded, the beam itself could not be easily detected from a distance, yet the spot clearly visible on a cloud deck.

I am also interested in the science behind lenses, if taking a laser beam which has been expanded to several inches, whether then placing a PCX cylinder lens in front of the highly expanded low divergence collimated beam would then allow the line to also have reduced divergence in the opposite plane to it. I've asked this before and have been told that this would be the case, but I am not sure, most of the individuals I've passed this question to in the past have not actually tried it themselves to see. Wish I could do so myself, but now that I am over seas and without my toys, I can't test! If this indeed does work that way, this would be a low divergence line (opposite to its plane) which could be viewed at a very great distance if the beam were first expanded to, for example, 12 inches, and then passed through a PCX cylinder lens (not sure of the correct term for one).

I find the idea of a uber low divergence line very interesting, perhaps it could be viewed from incredible distances, if flashed across someones view many miles distance. While I am interested in the answer to this, practical application cannot likely be achieved, I wouldn't want to accidentally flash an aircraft, I don't need that kind of trouble and as I pilot myself with several thousand hours logged, I understand. So, the low divergence line requires a very large diameter lens and the larger the diameter lens the more difficult it is to achieve 4 lambda as well as afford... so I'm trying to get answers instead of spending money to find out. I can afford a 2 lambda 24 inch diameter PCX lens, or afford to have a 150 x 150mm cylinder lens made for me, but I can't afford to spend that kind of money if I'm wrong and trying to get the answers I need. The potential problem of accidentally flashing aircraft can be solved, I would just need to move into IR and use detectors. This might seem like a silly effort, but my 144 MHz ham radio moonbounce antenna array which had close to 30 dBi of gain was a fun project to do too, some laughed at that hobby but I enjoyed it.

http://photos.imageevent.com/qdf_fil...gi%20Array.pdf

To jump forward, the mirror solution from a Dobson telescope seems like a better way to go than using a giant refractor at only 2 lambda. Just happens I was looking at some Chinese mirrors on ebay last night thinking about using those instead, but I still need to be sure placing a PCX cylinder lens at the output would produce a laser line at a highly reduced divergence.