Mirror types for CO2 lasers

[Mike Lysov]

Hi guys,

I was trying to get a spare set of mirrors and lens for my new laser but after I received a quote from my dealer I do not think I am going to buy the set from them. They want $350 for each mirror and the lens but it does not end there. They also asking $200 for shipping four mirrors and one lens from Taiwan to Australia. I think they just trying to rip me off.

Does anybody here know much about mirrors types? I was thinking there just 2 types maximum but there are four types at least
Si Mirror
Mo Mirror
Cu Mirror
K9 Mirror
That is according to an ebay seller for # 230926446319. Which one is the best and should be used with the laser running two GSI DC excited 140W tubes?
It seems I will need mirrors 38.1mm in diameter but I will measure the ones I have now before I buy spare ones. It is a bit hard to find mirrors in this size but I believe it is possible.

I have already bought 3" lens from the same guy on ebay as a spare one and I will try it as soon as I get it. It has costed me just $70 shipped via DHL from China,

[Dan Hintz]

You should be fine with copper mirrors, no need for anything fancy. Silicon mirrors are workable, but they're not quite as durable. Molybdenum mirrors are highly durable, but you'll pay for that durability (and you don't need it). No idea what K9 is, other than likely just a marketing name...

EDIT: I should add... most low-power machines are going to have silicon mirrors with a gold coating on them. They're dirt cheap and work well for the low powers we use. If you're looking for simplicity, these will be the easiest to find.

[Chuck Stone]

isn't this where someone inserts a link about making your own mirrors out
of an old hard drive disk?

[Michael Arruda]

Chuck- funny you should say that! I just made a set of mirrors out of a dead HDD platter yesterday for my Redsail X500. the mirrors that were on it were pretty bad- the first mirror was scorched pretty bad, and the second and third were scratched to heck. So, I made a set. Pretty easy, really- I used a 1" holesaw to cut the platter into rounds, chucked up some scrap poplar in my lathe, turned them down to 20mm, sandwiched a mirror disk between them, and used a parting tool to bring it down to the 20mm guide bushings. Worked out great. I am going to be refocusing the laser today, so we'll see how it all turns out.

-Michael

[Chris DeGerolamo]

isn't this where someone inserts a link about making your own mirrors out
of an old hard drive disk?

diylaser.midwestlaserartsdotcom/2012/01/get-your-co2-laser-mirrors-for-free

[Dave Sheldrake]

Si Mirror: Silicon Glass Gold coated, great reflective index, not good for anything 80 watts or over (not too hot on 60 watts either)
Mo Mirror: ​Molybdenum, very tough but the lowest reflective index, great if you miss cleaning or have a habit of dropping mirrors or if you have over 80 watt sources.
Cu Mirror: Copper, Below gold Si for reflective index but tough and better index than Mo
K9 Mirror: Close to worthless gold coated glass (likely from re-melted milk bottles), anything much over 35 watts and a spec of dust and they break. Designed for the "Hobby" series K40 lasers (the $500 ebay junk)

Si will last around 9 months to a year, Cu's will go a year or more (but do scratch easily) Mo will last up to 3 years or so, K9....well..if you really must and don't keep it spotlessly clean about 10 minutes before you poke a hole in it.

Win-Win aren't too bad but can be quite slow, try Cole CNC (ColeTech on ebay) they do the same gear at the same sort of prices with quicker delivery.


I think they just trying to rip me off.

Maybe, maybe not, a good mirror from II-VI infrared will go to around $200 - $250, RMI tend to be about the same, Zeiss if you really must is going to be about 10x that.If they are offering II-VI stuff then that price isn't too bad, if it's just generic Chinese then ...well....a tad overpriced maybe ;)

Some of the "HQ" stuff out of China comes from II-VI's facility they have there, not quite US quality but not far off.

The differences in reflective index is only 0.5% between the worst and the best so not really anything to worry about unless you are using a very high end source and need every last fraction of a watt output.

best wishes

Dave

[Robert Silvers]

RECI charges $70 for a 25mm mirror in single quantity.

Are the hard drive mirrors good at 100 watts?

[Dan Hintz]

Si Mirror: Silicon Glass Gold coated, great reflective index, not good for anything 80 watts or over (not too hot on 60 watts either)
Mo Mirror: ​Molybdenum, very tough but the lowest reflective index, great if you miss cleaning or have a habit of dropping mirrors or if you have over 80 watt sources.
Cu Mirror: Copper, Below gold Si for reflective index but tough and better index than Mo
K9 Mirror: Close to worthless gold coated glass (likely from re-melted milk bottles), anything much over 35 watts and a spec of dust and they break. Designed for the "Hobby" series K40 lasers (the $500 ebay junk)

Si will last around 9 months to a year, Cu's will go a year or more (but do scratch easily) Mo will last up to 3 years or so, K9....well..if you really must and don't keep it spotlessly clean about 10 minutes before you poke a hole in it.


Dave, I'm not sure where you're getting those numbers but they're pretty far from reality. I was putting over 70W into mine on a daily basis and they never once felt even warm to the touch. As I said earlier, Si is perfectly acceptable for a mirror. The vast majority of mirrors used by ULS, Trotec, Epilog, etc. are all Si, and they're good for hundreds of Watts. Absorption is typically <0.5%, and the difference between "quality" and "regular" is on the order of +/- 10% of that low figure.

I know nothing about the K9 mentioned, but the others typically are either highly polished with a coating to prevent oxidation, or they have a vacuum-deposition coating of gold, etc. Either way, there are very few on this board (Bruce Boone might be one) who have lasers powerful enough to warrant anything other than Si.

[Dave Sheldrake]

I'm not sure where you're getting those numbers but they're pretty far from reality

Professor Simon Widlake, Rutherford Appleton Labs Hereford.


As I said earlier, Si is perfectly acceptable for a mirror

Indeed, depending on the quality of the supplier. I simply addressed the standards of the mirrors available from the vendor the OP asked about.Mo is 8 bucks more and will last a lot longer as well as cover the Op against accidental damage or corrosion.


and they're good for hundreds of Watts

FOM = k/AX = k/(1-R%)X

Probably not good to put a PVD Gold coated Silicon mirror into a 600 watt Machine.


Either way, there are very few on this board (Bruce Boone might be one) who have lasers powerful enough to warrant anything other than Si.

Then why are sweeping "one fits all" responses given about Laser Optics in a lot of cases ?

best wishes

Dave

[Dan Hintz]

<sigh> I really grow tired of these matches on here. No one asked about a 600W machine as far as I can tell. I would take a wild stab and say 95% of the people running machines here are several hundred Watts and below, and the vast majority of those under 100W. There is no realistic advantage to Mo mirrors over Si in the machines typically seen here... if people are dropping mirrors, they have bigger issues to worry about. A large mirror should mean wider beam waist used. But if someone wants to argue against real-world use for the thousands of machines being run for many years on this forum alone, have at it... my answer has been given, take it with whatever size grain of salt you desire.

[Dave Sheldrake]

There is no realistic advantage to Mo mirrors over Si in the machines typically seen here

The op is asking about lens's from a specific vendor, that vendors own recommendation for the lens's they sell is NOT to use SI in lasers of 60 watts and over.


There is no realistic advantage to Mo mirrors over Si in the machines typically seen here

Put a win-win SI mirror in a 100 watt laser and it will crack.


my answer has been given, take it with whatever size grain of salt you desire

As I'm sure you are aware from Uni days Dan, The scientific method places no weight on a proposers own position that is not backed up by numbers. If an opinion isn't testable then it doesn't even qualify as theory.

best wishes

Dave

[Mike Lysov]

Thank you guys for so much details and help.

It seems there is a problem with choices for me. Two of my mirrors are 38.1mm in diameter the only mirror I can find so far in this size is Si mirror. Most of them available for sale are 6mm thick including the one sold on ebay. However I could find one seller that sells 4mm thick outside of ebay for $100 with postage. The other problem that the last mirror on the path and it is located on the head has hand written λ/0 45 degrees on it. I guess 45 degrees is not important as i is supposed to be flat and set at 45 degrees but what about flatness of 0. Nobody sells anything like this, the closest # I can find is 2. Is that such a big difference?

My mirrors are gold in colour, most Si mirrors are sold coated in silver.
The good news though that I will need only two mirrors 38.1mm, the other two used next to the laser tubes are smaller. I have not measured them yet but they seem to be 25mm in diameter. I hope for these two I will find more suppliers.

[Dan Hintz]

The other problem that the last mirror on the path and it is located on the head has hand written λ/0 45 degrees on it. I guess 45 degrees is not important as i is supposed to be flat and set at 45 degrees but what about flatness of 0.

This says the mirror is a phase retarder. It converts a linearly polarized beam to a circularly polarized one.

Looks like I didn't quite answer your question. I can't say I've seen a lambda/0 designation before... I'm wondering if the guy meant to write lambda/10 (missing the one). I see no reason not to use a standard lambda/10, however. Phase retarders are most common in Cu and Si.

[Dave Sheldrake]

http://www.iiviinfrared.com/CO2-Laser-Optics/reflective-phase-retarders.html

Although apparently "Phase retarders aren't used in low power lasers as they make no difference"

Australia
IMTS Laser Specialists
110 Proximity Drive
Sunshine West
Victoria 3020
Australia


best wishes

Dave

[Dave Sheldrake]

I'm sure (all sorted :))

Ummmm I was passing on information that Phase Retarders apparently make no noticeable difference in low power lasers Dan, I had actually learned from your earlier post that their use in low power lasers was moot and apparently the gains would be insignificant.(Later confirmed by II-VI when I asked) The quotation marks were added to show that the original information was not mine.

My apologies if the written word didn't come across as I meant or if I wrote it in a way that was miss-understood.

As it happens I think your probably a really nice guy (like many, you give up your time to help people, ergo unpleasant people rarely if ever do that), the fact we disagree on a few points doesn't confide that I have any thing personal against you.

cheers

Dave