newbie question about focusing lens

[Linda Smith Alabama]

From the photos of focusing lens I've seen online, they look amber and transparent. When I take mine out to clean it (from a used laser engraver I just bought recently) it's much darker and reflective, like a mirror. Is this normal, a different type of lens, or is it time to replace it?

[Rodne Gold]

Dark and reflective doesnt sound good at all - what laser and can you post a pic or the lens ( use some white well lit paper behind it so we can see the colour of the lens) - ie light the paper and NOT the lens so we can see the lit paper. Light source pointing on paper behind the lens.

[Linda Smith Alabama]

Oh this isn't so bad, maybe we've found our problem with loss of power? If the lens needs to be replaced, I'm just thankful to have found the problem.

I'm attaching a couple of pics. The first is the lens still in the tube, reflecting the camera like a perfect mirror. In the 2nd photo (that looks like a solar eclipse) I took the lens out and laid it on a tissue on top of a flashlight. Very little, if any, light is getting through.

[Linda Smith Alabama]

Oh, the laser engraver is a Chinese (Rabbit) 9060, 60-watt.

[Larry Bratton]

I suspect that is a huge part of your problem. Many times cutting and engraving problems are related to optics issues. I inspect mine every other day or so. Good luck, I hope this is the root cause of your problems.

[Linda Smith Alabama]

Thanks, I am hoping this is the problem too! Any recommendations on where to buy a replacement?

I took another pic of the lens laying on a tissue. The color is almost purple. The "smudge" on it is actually a reflection of the ceiling fan.

[Linda Smith Alabama]

Anyone ever heard of a Gallium Arsenide (GaAs) lens? This looks like what I have... purplish and reflective.

http://www.alibaba.com/product-gs/22...s_for_CO2.html

http://www.americanphotonics.com/gaas.php

[Larry Bratton]

Linda:
James Jaragosky is the Sawmill Creek resident expert on Rabbit lasers. He has one (maybe two) of them. Send him a PM and ask his advice on this. He is very helpful and has owned one of these machines for quite a while now and has acquired a lot of knowledge about them.

[Harper Abbot]

wow that doesn't look anything like the dirtiest lens i've ever seen. maybe it's a different material? being infrared, the beam may pass through something that looks totally opaque to the human eye. ever seen the "black" window on the front of an IR TV remote control?

ZnSe is the common material for lenses, but perhaps there are alternate materials that are being used?

EDIT: just saw the post two above - sounds like you have identified the lens as GaAs

[Linda Smith Alabama]

Yes, I'm sure it's a GaAs lens, looks just like the pics and description. Not sure if it needs to be replaced or not, and if so should I get another one like this or the more common ZnSe? I don't know if there's an advantage to the GaAs lens. Hope it was ok to clean it with acetone, that's what I've been using when I thought I had a "regular" lens!

[Linda Smith Alabama]

Thanks Larry, I PM'd him.

[greg lindsey]

I get my optics and mirrors from Laser Resourse. I believe they are a member here. Maybe you can give them a try.

[James Jaragosky]

Linda, I know that you have sent me a pm with this question; However I think it would help if I answer it here for others to see and add their expertise.

The standard lens that was most likely supplied with your machine is the Zinc Selenide, the GaSa lens is more expensive and is usually recommended for harsh environments.
I have no hands on experience with the GaSa mirrors, However I have read about them and from what I have gathered you GaSa lens should work as well as an ZnSe lens if both have been manufactured to proper quality specifications.

Because the previous owner has changed the lens type, I would check the mirrors as well. Poor quality mirrors can and will cause Thermal distortion. poorly made mirrors or lenses can both cause thermal distortion.

Thermal distortion:
A gold coated copper mirror has such high heat conductivity the temperature gradients on the surface are small, and the resulting distortion is insignificant. It also happens in a time scale of milliseconds, so the mirror reacts instantly to the beam being turned on and off.
A ZnSe coated mirror has 40 X more optical distortion than a gold coated copper mirror. This can cause the focus to shift and the spot size to alter with changes in power. More annoying is the time scale this happens in, around 20 - 40 seconds. So the laser drifts and shifts quite noticeably during the work.

This would be my best guess as to why you have better cutting quality at a lower power setting.

Please keep us advised to what you find out.
Best Regards
Jim J.

[Linda Smith Alabama]

This would be my best guess as to why you have better cutting quality at a lower power setting.

Please keep us advised to what you find out.
Best Regards
Jim J.

OK. In a nutshell, if cutting better in a lower power is better, then what do I need to get back to full power cutting? A new set of mirrors? Maybe a new focus lens? I have 60 watts and I want it at full power when its needed.