Hard drive platters and some co2 laser questions

Hello, I'm a student and as part of my A levels I'm planning on making a small 10-20 watt co2 laser based on a Liebig condenser, with an arc lengh of about 400mm and a bore of about 15mm. For the high reflector I'm considering using an aluminium hard drive platter if I can't get hold of a proper gold plated one, I am just wondering whether anyone has done anything similar? And will I lose power using a planar mirror?

Just had a few more questions come up and thought to save making a new thread I'd edit this one!

I'm planning on basing my laser on a Liebig condenser, the 400mm one here in particular Condensers, Liebig 400mm effective length means a 400mm water sleeve, so that'll give me a 400mm arc, and about 500-600mm between mirrors. Apparently the internal bore is about 15mm. I intend to use a germanium output coupler to reduce cost, but putting the dimensions of the condenser tube into this equation;

The optimum value for the OC reflectance is given by:


R=1-(Ld)/(500*D)

Where:
R = OC reflectance (as a fraction between 0 for non-reflective to 1 for totally reflective) mirror.
Ld = Length of the discharge (active medium, NOT the distance between mirrors).
D = Diameter of the bore.

Gives an ideal reflectivity of 95%, way above that of germanium's, which I believe is 50%. HOw much of a problem will this be? I want to keep bore size down as my vacuum pump doesn't draw the greatest vacuum, and I want the arc very well cooled, and I also don't want the whole thing to be too long, say 1 meter at the very very maximum. My power supply will be a half bridge of mosfets switching a rectified 2Kw variac into a rectified flyback, so I should be able to get good power and good voltage to strike a reasonably long arc.

Basically I'm wondering if basing the tube on a Liebig condenser is too restricting.... I'd be happy to go for it if I could get a zinc selenide reflector cheaply, but they're difficult to find at a student's budget! Any help is really appreciated.

Re: Hard drive platters

Well I know they work perfect for lower powered lasers, maybe someone with a co2 laser could try?

EDIT, forgot to say, make sure the platter is an alloy , some are glass or ceramic and literally explode when you try and cut them.

If you have a handheld laser, try shining it through the platter, if you see ANY light, don't cut it.

Re: Hard drive platters

Yeah that's an idea actually, so an appeal to anyone with a co2 laser; please can you shine it at the aluminium platters of a hardrive and see whether it's a good reflector? Ie does it get very hot? Ok thanks, I'll look out for that.

If I had a platter I would try it for you! I can say that the intercavity power is massive compared to the output so simply pointing a co2 laser at a platter is not a good test. That being said aluminium does reflect 10.6um very well.

I'll measure one later this weekend (if I remember). Power meter before and after is the best I can do. It isn't ideal, and it won't tell you if it's good enough, but it will tell you if it's bad enough... does that make sense? :can:

If you want to save yourself some time and do it properly, you can get gold mirrors for like $15 here: 25mm Gold Plated Reflection Mirror

They have a slightly cheaper 20mm version too.

i've tried alloyed platters on my co2 and they do reflect the beam pretty well. havent done any power loss measurement, but i did notice that it gets slightly warm after prolonged exposure.
i have also tested black anodized Al, but it melted it rather quickly

Thank you all for the help! That's great Cyparagon, that'll certainly give me an idea as to what to expect! Yeah I'm considering buying one as well, but I do prefer doing it all myself, but I'm still trying to source a concave mirror at a reasonable price, I'm just considering my alternatives now. Any opinions on basing the laser on a Liebig condenser?

Well my tube and/or PSU isn't super stable at low power, but I set it at ~2.45W. After the platter, it was around 2.35W. Put the sensor directly in the beam again to see how much it drifted; still ~2.45W. So... somewhere around 96%? Good enough? I dunno.

That's a good ballpark figure to go from, thank you very much!

Look what I just won! Mixed Germanium and Zinc Selenide optics for 10.6 micron CO2 laser | eBay A fantastic start to my set up, can't wait to get my hands on them.