How fast does the laser turn on?

[dirktheeng]

All,

I was wondering if anybody had a measuremnt or some data as to how fast a typical CO2 laser can turn on and off. Just to be clear, I am not interested in how long it takes to set a new power level via PWM, I am after the time it takes from the moment I give the on bit signal on the laser on/off line to the time I get to 100% of my laser set point power and the time it takes to get from that set point laser off once the bit is set to zero. I immagine this is very fast, but I am not sure. This affects how fast we can move through an engraving. I am hoping somebody can scope their power supply and find out.

[r691175002]

I doubt you will get any specs on chinese tubes, but RF excited lasers have rise times of less than 100uS and generally are much faster:
http://www.synrad.com/vseries/v30.htm

Note that the chinese tubes use a different process and are much, much slower. Getting a decent 3d engrave at much more than 5-10% speed (Probably like 3-6in/min) is pretty much impossible.

Measuring this would be far more complicated than scoping the power supply since the tube will lase for a short period of time after excitation stops. You might be able to get a rough estimate by jogging sideways at high speed and pulsing the laser on thermal sensitive paper or something and see how the line tapers off.

I think fullspectrum has more info on exact specs since they measure all the tubes they sell (supposedly for fast rise/fall times = better engraving).

[dirktheeng]

[quote="r691175002"] Getting a decent 3d engrave at much more than 5-10% speed (Probably like 3-6in/min) is pretty much impossible. [quote]

I hope you mean inches per second here otherwise a single line would take about a minute.... I think it is more like a second.

[dirktheeng]

[quote="r691175002"]Measuring this would be far more complicated than scoping the power supply since the tube will lase for a short period of time after excitation stops. [quote]

I meant to say scoping the power supply. Sorry for the confusion there. I would expect the time to stop lazing is insignificant to the electronics, but I could be wrong.

[r691175002]

I messed up my numbers, I'd have to guess but I think most 3d engraving sits in the 20-30IPM range so a full engraving can take a very long time on a chinese tube.

The rf excited stuff does way way better.

[lasersafe1]

I looked at a run with a scope before and I was seeing pulses of 15us. The laser seemed to respond. (Chinese tube and power supply).
I spoke about it in depth here: http://www.buildlog.net/forum/viewtopic.php?f=6&t=36&start=20#p501

I do granite engravings at 800mm/sec all the time. This is 30ips. Since the black dots are at a 254dpi resolution, you could calculate the length of the pulse.

[dirktheeng]

This is such good news! I was looking into high speeed shutters to use, but this is better and easier.

By the way I did find an ULTRA fast shutter that can be made from the servo arm of a hard-drive.

So at 30ips and 254 DPI, this means you can turn the laser on and of 4 times in each pixel. So theoretically, you could run 30ips and 1024 DPI and get the laser on and off once for each pixel (wouldn't provide much time to mark the substrate, but it would at least power up and down).

[lasersafe1]

theoretically.... Don't quote me on those numbers. I simply looked with a scope and saw the command outputs, and the resulting image looked good. I didn't actually prove that the tube responded though. I believe of all people on the forum, Henry at Full Spectrum Engineering could give you the confirmed answer. He has a fast photodetector that can see the actual pulses. Perhaps you should PM him since he might not be following this thread.