Acrylic Vs. Glass Lens (which is better)

Hello all. :wave:

I've been looking around and found some conflicting information... :evil:

Some say that acrylic lens are actually better than glass, and some say that glass are better than acrylic due to some part of the plastic melting. :undecided:

Are acrylic lens okay for lasers above 200 mW? (ebay sellers and information say that they are not okay for it)

Is the power increase that significant over using glass and acrylic?

And, I understand that AR coatings help increase power output quite a bit. What happens when you use a lens that's coated for 405 nm with a red laser? Or vice versa?

Le Quack;

It is the AR coating that can make the difference.

Plastic lenses are less likely to have the AR coatings.

That means they transmit LESS of the laser light . . .

and also heat up with higher power beams.

Quality lenses are AR coated and made of GLASS for the visable wavelengths we like to see.

AR coatings can be narrow-band (single color) or wide-band (multi-color).

Very few sellers even know the wavelengths that their lenses will pass efficiently.

LarryDFW

The acrylic vs glass debate is often complicated by issues that really have nothing to do with acrylic vs glass:

1) The melting issue is really about acrylic vs metal. With the typical 3-element glass lenses, you have a metalic M9x0.5 mount holding the lenses in place. With typical acrylic lenses, you have a black plastic M9x0.5 mount. It's the black acrylic mounting that can melt, not the lens itself. Obviously, the metal on a 3-element glass lense will NOT melt.

2) When people compare acrylic vs glass, they're generally comparing 1-element vs 3-element lenses. That's sort of an unfair comparison. If you look at 635 multimode diodes, the glass 3-element red-coated lenses produce almost exactly the same output (in my experience) as the acrylic 1-element red-coated lenses. But this isn't because the two materials are on par. Rather, it's largely due to the fact that with the glass lens, we have the beam passing through 3 pieces of glass instead of 1.

3) Coating vs no coating was addressed above, so I'll leave it out of my discussion.

4) The question: "Is acrylic safe for above 200mW". My answer: Yes and No. For me, for lasers I build, acrylic is just fine for 500, even 600mW of power. That's because I never use my lasers for burning. What's the significance of this? Well, to burn with a laser up-close, you position the lens further from the diode, which means more of the output hits the black acrylic mounting hardware. Since this is the portion of an acrylic lens that melts, you're in trouble. But as mentioned, if you're not here to "bern stufff, yeeeehaw", then you'll probably be just find with an acrylic focused to "infinity".

Finally - I'll address cost. A red-coated acrylic and a red-coated 3-element glass lens cost virtually the same when purchased a few at a time. You're looking at about $3 to $5 per lens. No big difference.

Some of the AR-coated acrylic lenses will transmit light in the red spectrum (635-660nm) better than the equivalent AR-coated glass lenses. You should not, however, use acrylic lenses with 445nm or 405nm lasers as they can melt and are usually AR-coated for red anyway.

(read rhd's explanation, much better)

The comparison is odd indeed, the typical acrylic lens is a single lens, fitted by a black plastic holder. Glass lenses are usually 3 element constructions with metal fittings.

Personally i prefer the glass lenses, but only with the proper coating ofcourse. I think the beam quality is better, but i would not say the raw power output is higher.. the latter could in fact benenfit from a single lens system vs a 3 element construction, so it also depends on what your priority is.

It surprises me that we don't have generic/cheap SINGLE element glass lenses. They seem like a no brainer. Simpler (cheaper) to create than 3-element lenses (if done in bulk commodity form) but better than acrylic.

IE: why not exactly duplicate the acrylic lens specs, in glass?

Glass is easier to clean than acrylic too

rhd said:

It surprises me that we don't have generic/cheap SINGLE element glass lenses. They seem like a no brainer. Simpler (cheaper) to create than 3-element lenses (if done in bulk commodity form) but better than acrylic.

IE: why not exactly duplicate the acrylic lens specs, in glass?

Click to expand...

About 3 years ago I bought a rgy scanner on ebay. It was made in China and
had a glass lens on the red which appeared identical to the standard acrylics.

It also came in the plastic housing, and was not coated. I have only seen one,
and should still have it. If I can find it, I will upload a few pics...

So they do exist, just where to find them remains the big question.

Single element glass lenses are much more expensive to produce than 3 element. The reason is in order to get good collimation with a single element, the lens must be aspheric in profile. With acrylic this is very easy; just injection molding plastic. With glass aspheric lenses are usually precision ground; a process much more expensive than spherical manufacturing techniques.

Spherical glass lenses are very cheap and widespread because the constant radius of curvature makes them easy to grind.

rhd said:

It surprises me that we don't have generic/cheap SINGLE element glass lenses. They seem like a no brainer. Simpler (cheaper) to create than 3-element lenses (if done in bulk commodity form) but better than acrylic.

IE: why not exactly duplicate the acrylic lens specs, in glass?

Click to expand...

We do have single-element aspheric glass lenses with quality AR coatings . . .

but they require more complex manufacturing and therefore cost more (~$45 today).

They do deliver the highest power output as verified by extensive testing I had done,
when I was selling those aspheric lenses.

LarryDFW

I reckon its mostly a mfg cost issue as well, but there is no reason to just assume that acrylic is an inferior material to make lensens out of in the first place.

Glass may be mechanically harder, but other than that, acrylic has few dowsides when using visible light.

Acrylic can be molded though, where glass has to be ground basically from a rod/disc down into the proper shape for a lens. The downside of molding is that the final dimensions will not be as precise as those in ground optics, and this adversely affects the beam quality from the typical acrylic lens.

Obviously it is possible to ground precision aspheric glass lenses too, but that's an expensive ordeal, resulting in $50-ish lenses that are probably a bit too expensive for the average user to purchase - especially since they add little benefit in things like simple pointers or close range projectors.

Le Quack said:

Hello all. :wave:

I've been looking around and found some conflicting information... :evil:

Some say that acrylic lens are actually better than glass, and some say that glass are better than acrylic due to some part of the plastic melting. :undecided:

Are acrylic lens okay for lasers above 200 mW? (ebay sellers and information say that they are not okay for it)

Is the power increase that significant over using glass and acrylic?

And, I understand that AR coatings help increase power output quite a bit. What happens when you use a lens that's coated for 405 nm with a red laser? Or vice versa?

Click to expand...

You asked a question very similar to another poster. Here's the answer I gave them. I do think they are intended for low power applications.

Not true about acrylic lenses. They can be just as precise as glass.
Give Edmund Optics a call and request their free catalog. It's chock full of all kinds of info and stuff they you'll find useful Phone: 1-800-363-1992. In the mean time you can look around their site Contact Us - Edmund Optics