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FrozenGate by Avery

Wavelenth vs lens choice

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bl4ckj4ck777

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Alright, this is probably a noob question, but I can't seem to find any other threads that explain it (not saying there isn't one, I've just given up on looking).

I did however find that basically from your LD wavelength, you can determine what the focus can be, which if I remember right is 1/2 of the LD wavelength.

So would my lens choice be affected by what my wavelength is? Or are all lenses doing the same thing no matter what wavelength you choose.

For instance, I have a 1W 808nm LD, would I pick a lens that is around 404nm for optimal results? I also know that glass vs acrylic plays into this, but I'm just trying to find out what would give me the best results in terms of more focus (which should increase the burning power of the laser).

Again, sorry for the noob question.
 





I don't understand your question... Do you mean that you are going to buy a lens that is suited for 404nm light? If so :wtf:... You will need a lens suited for 808nm application.

Next the focus is determined from the lens it self. Usually lens come with a set focal point, this is the optional distance away from the lens to get the best focus. On an Aixiz module for example, it has a adjustable focus, allowing for shorter or longer focal distances.

Lastly you can buy coated lens. Your wavelength will affect the performance of the lens. For example, 405nm AR coated lens will give a power increase typically in the 25-30% mark for wavelength of 405nm, where as for lower wave lengths such as 660nm (red) the 405nm AR coated lens will not give any boost in power, and may inhibit the output power, resulting in a loss of power.

Hope that helped! -Adrian
 
Yes, lenses will focus different wavelengths at different distances, but it's mostly going to depend on how the lens is designed. It does mean that one lens may not focus all wavelengths of light that go through it the same; so if you want to combine beams of different wavelengths, you'll need to focus them before combination.

What's often more important is choosing a lens with the correct anti-reflective (AR) coating to match your wavelenth(s) in question. The focus of your lens can usually be changed, but rarely the AR coating, and you'll want as much energy as you can passed by the lens.
 
Alright, that helps, but I'm still a little confused.

Basically, from what I'm understanding, the focal distance and AR have to do with choosing a lens based upon wavelength.

I don't understand your question... Do you mean that you are going to buy a lens that is suited for 404nm light? If so ... You will need a lens suited for 808nm application.
Click to expand...

Well, that particular question was actually a two part question, and I may have not written it to sound that way, but I remember reading somewhere on these forums that you can only focus a laser to about half it's wavelength, so first off I wanted to clarify that.

Secondly, I wanted to know if the number rating on the lenses themselves were related to that. i.e. a 404 nm lens being the ideal lens for an 808 nm LD or if the rating is directly made for each wavelength, i.e. an 808nm lens being ideal for an 808nm wavelength.

Basically, with my laser application, I'm making a burning laser and I'd like to know how to choose the lens that will give me the most focused point (best burn). I may have worded the question in a roundabout way, but I didn't want an answer like "just use this lens" because I wanted to know WHY it was the best choice if I decided to use lasers with other wavelengths.

On top of that, can lenses actually change the wavelength of a laser? For example, could I increase the wavelength of my 808nm laser (infrared and not visible to the human eye) to make it more in the 600nm range (red?).

Hoping that all makes sense.
 
Ohhh I see... If you are buying a lens for a 808nm laser, you will need a 808nm lens. Now I don't know if the actual 808nm lens is made for 404nm light, in order to increase 808nm light, but I think focal point will mainly depend on the construction and quality of the lens. As Bionic-Badger said, different wavelengths will be focused by the lens differently and for this reason, certain lens are made with a bandwidth typically +-50 nm of light.

On top of that, can lenses actually change the wavelength of a laser? For example, could I increase the wavelength of my 808nm laser (infrared and not visible to the human eye) to make it more in the 600nm range (red?).
Click to expand...

The only way I know of doing this is with the use of a doubling crystal. I know that a dpss green laser actually pumps IR light into a doubling crystal that takes ~1064nm and doubles the frequency to ~532nm. As far as I know this is the only way to change the color of the output beam. Please expand on this guys!!

Hope that helps! -Adrian
 
Thanks a ton, that helps out a lot.

Any good sources for buying said lens/crystal? Cheaply if possible, since my wallet is extremely tight at the moment. I'll poke around some on the forums, but I don't remember seeing much in the way of 808nm lenses.

If I'm understanding correctly though, the doubling crystal could take my 808nm IR (invisible) beam and make it more of a 404nm beam (roughly purple).

Just curious as well, is it possible to double a doubled beam? I'm assuming there would be a power loss from the resistance of the light traveling through more and more crystal, if it would even be possible at all.


Anyway, thanks for the help so far. I'll post my project here if I ever manage to get all the parts and get it working properly (DAMN EBAY!!).
 
bl4ckj4ck777;

I think you are confusing a couple of different concepts.

First of all, choose the lens based on the divergence of the Laser Diode you are trying to collimate.

The divergence of a Blu-Ray diode requires a short FL lens,
to collect more of the light power and collimate it into a small narrow beam.

Your hi-power 808 LD will require a larger lens with a slightly longer FL to focus the beam properly.

I don't think you understand "doubling crystals" and their limitations. That would require a lot more reading. Green DPSS articles would be a good start.

LarryDFW
 
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From what I'm understanding doubling crystals are very specifically made, not something you can just use on any laser. Not to mention they cost more than the laser itself in many situations. I'll admit I was just trying to get a quick answer when I asked if they could be doubled more than once, but I figured there might be someone here who'd actually tried. Maybe it could be done with more than one kind of doubling crystal? I wouldn't know, I'm just a noob here.

bl4ckj4ck777;

I think you are confusing a couple of different concepts.

First of all, choose the lens based on the divergence of the Laser Diode you are trying to collimate.

The divergence of a Blu-Ray diode requires a short FL lens,
to collect more of the light power and collimate it into a small narrow beam.
Click to expand...

I'm obviously confusing concepts, or I wouldn't have started the thread in the first place. :D

If you would like to try and help me some more, maybe you could refrain from using acronyms so that I know what you're talking about. For instance, I have no idea what a short "FL" lens is and when I try to google it, it comes up with any number of acronyms, even when I try to narrow it down to lens related topics. This is probably just because I'm inexperienced with the lingo and I don't know exactly what to google.

Perhaps you could tell me if there is a way to determine the divergence of a laser (is it related to wavelength for instance?).

Sorry if my ignorance is bothering you, but the truth is I have only a very limited understanding on lasers, and reading theories only helps so much when I'm trying to figure out specific questions with fairly specific applications.

Hope I haven't offended anyone, that wasn't my intent, thanks for all your help.
 
First start here: http://en.wikipedia.org/wiki/Lens_(optics))

FL = focal length. Imagine you have a bunch of light rays being emitted from a point and fanning out in a V shape. If you put your lens in front of the fanning out light rays and position it such that the point where the rays originate is just at the focal point of the lens, then the lens will bend the rays so that they come out the other side in a parallel beam. Move forwards or back a little and the rays will converge or diverge, instead of being parallel. People "burn" by positioning the lens so that the rays that exit converge into a waist (and then diverge) and the concentrated amount of light at the waist is what they burn things with.

For making a parallel beam, imagine two lenses; one with a short focal length and one with a long focal length. You have two identical laser diodes set up next to each other with one lens in front of each and the diode at the focal point of each lens. The setup with the short FL lens will have a narrower beam because it's closer to the diode, collecting the light rays before they've spread out as far as the case with the long FL lens.

People say short FL is better for blu-ray because the raw emission of blu-ray diodes fans out fast and the short FL lenses will still allow the beam to be decently tight.

This is just the briefest description of one use of one type of (converging) lens. Check wikipedia for more.

So to recap, the only numbers you need to look at for lenses available around here are:
1. the # designating the type of AR (anti-reflective) coating which will be the wavelength of light it's meant for, or the word "broadband" if it's good for multiple colors. This is important because without an AR coating, you'll lose likely over 10% of your light, and with the wrong AR coating, possibly more.
2. Focal length which will give you an idea of how thick your beam will be after you collimate it into a parallel beam.
 
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seeing it seems that answer is going in a big circle. let me try this. an 808 wavelength will come to a specific point or point size base on all other things being equal for a specific lense.
meaning that second 808 with the same lense and all other things being equal will create a point size equal the other 808.
on any of these lazer specs or sizes there should not be any questions at all. I am sure the engineers that work with these lazers will go to a chart thats been prefigured and not have to do any guessing. my question is where I should be looking for ste standards.
thankyou
 
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