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Hemlock_Mike 12-08-2008 04:43 AM

RF excited CO2 lasers
Now that I have my tube inside the pipe, I have designed the housing for the driver, PWM and extra heat sink. This housing will be a piece of aluminum about 13" long and formed into a U shape.
The 18650 cells will attach to the exterior of the pipe.

NightStick -- I hope you get your transistor tomorrow.


nightstick 12-08-2008 05:49 AM

Re: RF excited CO2 lasers
Mike. I hope it comes tomorrow. cant wait to see the burn again I worked on my box a little more tonight, its looking really good I will put some pics in here tomorrow, I changed and ajusted a couple things I need to put a carry handle on it and add at least one battery tube with 18650s, that will all easly fit inside the enclosure. this has been a fun laser build for sure... I would love another one just to make it complety portable.. I might just get a tube only, :) and mess with an amp and a cb who knows

Cyparagon 12-08-2008 05:14 PM

Re: RF excited CO2 lasers
Do the RF versions carry similar efficiency ratings to those pumped by electrical discharge?

nightstick 12-08-2008 08:18 PM

Re: RF excited CO2 lasers
Maybe Mike can help you with that question Ive never had anything but rf generated co2, but what is cool is I can hook it up to my ham radio on 27.119mhz with about 50watts key the mic, and watch it burn :) and they normally run on 28 to 30 volts about12 amps for power supply.... :) Mike, I replaced my power transistor got it at noon today and was burnin by 1oclock its working great not bad for a $36.00 fix that would of never happend if I would of checked coax cable :D

Hemlock_Mike 12-08-2008 08:24 PM

Re: RF excited CO2 lasers
Congrats -- I knew you could do it. *;D

As for efficiency, the HV may win. *10,000 volts @ 18 mA vs 26 volts @ 14 Amps !!!! *I still like the RF because of the lower voltages and no water cooling.


nightstick 12-08-2008 10:57 PM

Re: RF excited CO2 lasers
and you can mount them on top of your truck with a 150 watt cb amp and cb and your in bussiness ;D thats a joke son :o Mike the plywood is popping into instant flame with this new transistor do you think I need a pwm from Chris what are the benifits,,,I guess to be able to turn it up and down Right? how long can you run your laser before it gets hot to the touch mine is about 40 seconds but I have run it for a minute and a half at a time Lynn :)

Hemlock_Mike 12-09-2008 02:12 AM

Re: RF excited CO2 lasers
The PWM will reduce the average power and current draw. I can run mine around 5 amps for minutes.


nightstick 12-09-2008 05:05 AM

Re: RF excited CO2 lasers
I was doing a little distance testing and at 12 feet it was still turning the plywood red hot 15 feet was just smokin and turning the wood black not too bad ;)

Hemlock_Mike 12-09-2008 05:28 AM

Re: RF excited CO2 lasers
Fun up close but these, like most lasers, will need some lenses!!! Sadly, ZnSe is a bit pricey :(


Tottish 12-09-2008 01:41 PM

Re: RF excited CO2 lasers
I don't know about the benefits but I remember Chris recomending not driving them above 95% once upon a time. Maybe the last 5% only contribute to the over alla Ampareage and heating of the module and not so much to the out-effect? So I guess that could be of interest to you since you're planning to use batteries.
The PWMs I made does not have any max-limit by default though. Either you just don't turn it all the way up or you could add a 50Ohm resistor to the possitive terminal of the pot and then you have a maximum of 95% dutycycle.


nightstick 12-09-2008 03:32 PM

Re: RF excited CO2 lasers
thanks Tottish, good to see you, I am gona try one of your pwms I just had to put a new power transistor in my amp I shorted the old one with bad coax but everything is working good again :D

Cyparagon 12-09-2008 03:45 PM

Re: RF excited CO2 lasers
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For those looking into getting lenses, eBay and laser research optics are both good sources. I've owned a GaAs from ebay, but it cracked due to abuse. I currently have a 3/4"diameter 7"FL ZnSe from LRO. My CO2 burning videos from a while back used this lens. They unfortunately require registration to view pricing, so I'll list a few entries for those interested.

Long focal length:
+ Easier to find the focal point
+ Much less chance of debris on the lens due to the distance
+ Cheaper (less material required for a flatter lens)
*- larger focal point (less overall intensity compared with a short focal length lens)

With a lens, CO2 lasers are FAR more fun! It's definitely worth an extra $100!

Here is a steal on ebay. $42 shipped for .75"DIA 7.5"FL meniscus assuming no one else bids (and it looks promising)

Hemlock_Mike 12-10-2008 12:43 AM

Re: RF excited CO2 lasers
Chris said that they show max efficiency with 90% PWM @ 24 kHz. I've never graphed that but I did find that low duty cycle seems to increase heating on my driver.
I plan to add fixed resistors to the pot to set ~30 to 90% on mine when I get to that point. I formed the driver housing for my "gun" and my bend allowances were poor :( That room at the welding shop was freezing cold >:( I made another today.....

+FL lenses are good for close burning as in those engraving machines but I need a ~-18mm FL for a beam expander. I'll keep watching. LRO appears to have good stuff and I may have to use them!


Cyparagon 12-10-2008 02:19 AM

Re: RF excited CO2 lasers
1 Attachment(s)
18mm is quite short indeed! It may have to be a custom job. Here are their prices for concave lenses, but they only go as short as 25mm.

If a very small .4"DIA (10mm) is large enough, this one from ebay isn't to bad at 20mm FL

Hemlock_Mike 12-10-2008 02:27 AM

Re: RF excited CO2 lasers
I looked at that ebay one -- coated for erbium :( Thanks anyhoo !!

Short FL for a diverging lens isn't unusual. I can also use a PCX with very short FL. I keep watching.


nightstick 12-10-2008 11:31 PM

Re: RF excited CO2 lasers
Mine is still going strong I guess I got by without tuning the antenna or biasing the transistor, thats good because I didnt want to make jumpers for my watt meter anyway... :)

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