Lens to Fix Divergence - Help

Hello!
I need lens to fix the beam divergence of my laser pointer and I need help choosing them.





I bought a BLUE 450nm 1W to 2W laser pointer from selllaser.com.
The laser is capable of burning skin, plastic, and non-white paper without ignition at a close range but the beam diverges allot, rendering it useless at over 3m 10feet.
The original lens are adjustable, but cannot be adjusted to focus the beam any further, only to diverge it even more up to 45º.
The beam is shaped like a rectangle. The dot's dimension's at a surface very close to the laser are ~2mm*5mm 0.07874*0.19685 Inch.

Basically I need some lens to correct the beam divergence,
I measured the divergence angle (relative to the straight line, with the original lens set to minimal divergence) by shooting the laser pointer at a wall from 25m 82feet away exactly.
Then I measured the size of the spot, However, because of the Blur of the laser light the dot was now a gradient of light intensity. This made the boundaries of the laser dot not well defined, so I measured a Max and min size for the Width of the dot.
With those dimensions I calculated the Max and min Divergence angles to be 0.120321º and 0.080214º. *

I found a nice lens supplier in the UK Precision optical components subassemblies | Interference bandpass filters | Custom Optics.
I need help choosing the appropriated lens to fix the divergence of the laser beam. To make the beam a straight line and make the dot's size the same at large or small distances.



Is such lens possible? What type of lens should it be? What should be it's focal length? What material do you recommend for it?
To take the laser beam that is diverging by 0.120321º and make it straight. What is the lens type, shape and focal length that I need?

That lens will be very close to the laser source. (beam size = 2*5mm)
The dot can be always rectangle shape, but this is optional, I do not want to change the dot's shape, just focus it and make it a perfect line.
Since the original lens can be adjusted to diverge the beam much more, I have some top margin.

So please, help me choose and calculate the lens I require to make my laser beam straight :thanks:.

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Another wish of mine is to converge the beam into a small point, I tried using lens from plastic seeing glasses (+4.00D). It worked but the lens reflected much light back, cutting down allot the power to the target. I tried using these lens to make the beam a straight line but with no success.
Hence I will also get some focusing lens to burn things at a close range 30cm 12Inch, this is easier for me to choose but if you have some recommendation on the lens material please do tell.

If there is a way to make the beam straight and the dot size smaller then original at long distances that would be great! Maybe with two lens? but I need help calculating that.

The problem is the laser you bought from sellaser is a fail. 450nm @ 2W? What?

It sounds like you have a 445nm, but I really doubt it's outputting 2W.

It also sounds as if your lens is not centered properly, and that's why you don't have a straight beam.

As far as I know, 445nm requires a significant array of optics to correct the massive divergence and can not be simply accomplished with a single lens.

I don't know what you're asking. Are you trying to make the beam square? If so just get an anamorphic prism pair or cylindrical correction optics.

If you're just trying to improve the divergence overall get a beam expander.

Yes, the power is over 1W up to 2W, I said 2W as it's top to make sure the lens you'd recommend can withstand the power. Even at low battery it can burn through black CD casing in 10sec. Of course "amount of burning power" is not a good way to measure power because it depends on the focusing, which I have little.
My problem is the beam divergence. Yes, the original optics are bad but now that I'v bought the laser there is nothing I can do about it is there? The laser is Chinese, it costed me 160USD so I think it's still worth the price.
Back to topic please.

Like I said I want to cancel the beam divergence. Making the beam's path a more perfect straight line. It has the power, and much potential for further hacking, like I am trying to do.

I just need to find some good lens to put over the original lens to fix the beam's path and divergence.

I know almost nothing about optics. That is why I come to ask help from you. What is this device "beam expander" and where can I find info about and where I can obtain one suitable for my laser and needs?

manueldois said:

Even at low battery it can burn through black CD casing in 10sec. Of course "amount of burning power" is not a good way to measure power because it depends on the focusing, which I have little.

Click to expand...

Yep using burning power to estimate power is not a real precise measurement. Here is a 1.6W laser vs CD case. It is a tad quicker than 10 seconds.

We'll invent a weird base unit like a "candela" to measure burning power, only based on how quickly CDs or balloons get burned. The "balloonela" or the "compactdiscela".

Again I underline that I created this post to get help on what lens should I choose to fix my laser beam divergence.

I do not really care at the moment about it's power, nor do I believe it's exact power is important in order to choose the appropriate optics.

When I get the change to test my laser's power using a more accurate scientific method I'll be sure to report back to you, Later.

Based on my experiment to measure the beam's angular divergence I hope someone can help me calculate the exact lens characteristics.

So please, any tip on the optics, lens or lens apparatus needed to fix this beam's divergence?

As stated before and found with a very quick search it will take a large setup of optics that will leave you with a not so portable laser and some loss of power. See this post about different options which was one of the first found with a search for "445 Correction".
http://laserpointerforums.com/f49/dreamlasers-have-beam-corrective-optics-56721.html#post802527

KGB_Productions said:

IF you are looking for specially coated optics for beam correction try here....


Cylindrical lenses coated for 445

Cylindrical lenses are 'go'

Anamorphic prisms coated for 445

Anamorphic prisms are go

Click to expand...

Thank you DTR.

If I understood the post properly , these lens are special because they are Anti-reflective coated, am I right?
Also, these lens are cylindrical because of the laser's beam rectangular shape?
What happens if I use simple AR convex lens?

Still I am confused about the size of these lens. As seen on that post they look quite big and so I understand why you say it'll be hard to put inside a handheld.
However I seem to find the same type of lens, cylindrical with AR, in much smaller sizes only 1cm diameter.
Small lens link

Also I do not comprehend if the problem is solved with just one of this lens, well chosen, or if I need various lens?
What extra lens do I need?

These are very expensive, hence I need all knowledge I can get before buying.


I think I did not leave it very clear that these lens would go "over" the original lens. I will use these new lens (or apparatus) in sequence with the original lens.

They're special because they're both cylindrical AND have an AR coating for 445nm (or broadband). Cylindrical lenses are relatively uncommon themselves, but to have them coated for blue/broadband wavelengths means you need to buy them from somewhere like Thorlabs (e.g. anamorphic prism pair; cylindrical lenses). They may even cost more than your laser. The end result is that these lenses are expensive and hard to source; most people just settle for the bar shape.

In your case, it looks like the lens is out of focus in general as the spot size is just large overall. Try focusing the lens down you should be able to at least reduce the size of the resulting spot, even if it retains the bar shape. You'll need to do this anyway even if you're using cylindrical lens pair/prism pair to correct the fast axis (the axis one that diverges faster).

If you're still hell-bent on correcting your beam to a square shape, you first need to collimate one of the axises (usually the slow one), and then you put those corrective optics in front of your regular optics and correct for the other axis. The lenses are cylindrical (or prisms) in order to only correct a single axis without affecting the other.

Oh, and for putting these things in a hand-held, for the cylindrical lenses, they will need to have short focal lengths and be positioned precisely. I don't know if you're have enough room. The prism pairs might be more doable, but as these optics were never designed for handheld lasers, your mileage may vary.

That explains they'r price...

I tried moving the original lens close to lens but since everything is mounted on a steel frame I'd have to unglue the lens from they'r support to move them closer to the source. I'm not going to try this, I'll fail and break the lens.

I Do Not Want To Make The Beam A Square.
I am OK with a rectangular beam, in fact I do not care about the beam's shape at all.
My goal is to focus the beam at a distance, regardless of shape.

I guess I have three options now:

either I scrap the original lens and order a new custom-made lens. Solving for divergence and possibly even increasing power(?)
or I order a non-AR coated lens to put over the original lens,
or an AR lens over the original, (cylindrical or other shape? (do not care about beam shape)).

The first option seems the one that'll give me best results.

So I need cylindrical lens anyway right? (or the prisms)
Because the beam is rectangular, I have two different divergence axis, I need a lens that will apply one amount of focusing to the fast axis and another degree of focusing to the slow axis?
Hence I cannot use spherical lens? I need two cylindrical lens, one for the fast axis another one turned around 90º for the slow axis?
That makes sense... Was so confused about 2 different divergence angles.

That means I have to repeat my experiment and measure both the slow and fast divergence axis, then, with you'r help we can calculate the focal length of each of the two cylindrical lens.

To reduce the cost can I put both lens very close to the source in order to reduce they'r size?
If I can do this I need lens with only ~2 millimeters in size, and since I'm ordering custom-made maybe small is cheaper.
Now that supplier I found also makes custom optics, and they'r "standard" AR coating has a minimal for reflectivity on 445nm:

They'r data sheet for the AR coating

Will this AR coating suffice? Am I right about 2 cylindrical lens with 2 different focal lens?
If I measure the fast and slow divergence can you help calculate the focus length of both lens in order to reduce the beam divergence?
What approach should I follow, re-do the whole optics or add new optics to fix the origin ones?

Thank's for you'r help!

Why don't you post a picture of your host and we can see if the lens can be adjusted. Just because they're glued doesn't mean you can't unglue them. Hell, the lens may be inferior anyway, and you might do yourself good by replacing it.

No, you don't need cylindrical lenses or prism pairs just to reduce the divergence of your laser. You only need the cylindrical lens or prism pair if you're trying to correct for a single axis (i.e. trying to make a square dot). You can use a regular convex/concave pair of lenses to focus the entire beam (both axises); the beam will retain the bar shape, but at least one axis can be focused down.

Still, using additional lenses is not the optimal way of solving your problem. If you add more lenses, you'll have more losses, even with AR coatings. Plus it is a real pain to get those lenses perfectly perpendicular to the beam unless they're in lens holders and fixed to your module (much like the lens in the laser you've already got).

Rather than use more lenses in front of the lenses you've got, you would probably be better served just adjusting the current lens you have in your laser module. Yes, I know you're afraid of breaking it, but even if you have to replace it, it'll probably cost you less than finding some other pair of lenses to try and compensate for the one you've got--assuming you can even mount them properly to do it.

So I would post some pictures of your actual laser and let us see if you can just, for example, screw the lens to a better position. Another thing you might want to get for this operation is some goggles. It's really hard to focus something like that laser if the spot is hard to observe. I've even tried doing it with a webcam and a laptop so I didn't need to run to the wall to see if the dot was smaller.

Finally, it may not be worth your time anyway. If I recall, the dot I had on the wall with my own handheld 445nm laser was pretty large too, if only because it was pretty hard to get it adjusted just right.

They are glued to the steel and super-glue can be tougher then iron if over a large surface.
The lens screws in the frame to be near the laser diode.
So near in fact I think at the max screwing the lens touch the laser diode's tip, or they'r just separated by an hairwidth.
Even if I did manage to take out the lens I do not know if I can get the lens any closer to the laser source. As it is the space between the lens and source already looks very very thin.

But if these lens are so small maybe I'll only need lens this also this small.

I like the pen-style. Its very neat! So I'm thinking about drilling the original optics out of they'r support (that "head" that screws in) and putting some other optics. Like this I have new optics but still easily adjustable, and the strength and beauty of an iron frame.

So I need some very small optics like 5-8mm 0.2-0.3inch diameter. (I can drill through the head in different sizes but would be even better if the lens can fit where the original ones did.
I can adjust the distance from lens to source from (+0) to 1.5cm 0.6Inch.
Do you think I can choose such lens that, by changing it's distance to source by just that amount, I can either make the beam straight in one position for the lens, or make the beam focused to a point near me in another position for the lens? Like two modes for the same lens depending on the distance to source. If that's possible that'll be great!

Tomorrow I'll measure the divergence of the source with precision so we can figure out an appropriate lens to make the beam straight, ok?

Should have came here before I bought it lol....

OP doesn't care about beam shape. Tell him to get a beam expander.