PWM vs CW for laser cutting/etching

[PCfreak]

What are the trade offs for pulsing a diode to reduce average power vs CW at a lessor power for cutting/etching applications? (I'll be using a 1W 405nm laser diode)

I'm building a RepRap style CNC Laser cutter / etcher, primarily for PCB fabrication using the black paint and direct UV exposure methods. Found a simple LM317 based driver capable of TTL modulation at up to 1Mhz that also has a linear current response to DC input 0-5v. (http://www.repairfaq.org/sam/ldschpcb.gif)

I'm trying to figure out if I should add circuitry to the driver input to reduce stress on the diode from intensity changes. At the moment I'm looking at a max frequency of about 62khz I think.

 

[PCfreak]

From what I've read so far, pulsing the diode at low duty cycles allows for higher optical power per pulse. I imagine for cutting, this would be desired as you want to vaporize as much material as possible per pass instead of just burning it. I'm also guessing that at the low speeds required to do anything at this power level I shouldn't have any problem with gaps between pulses.

I suppose for engraving I would want a large spot size anyway, so adjusting the focus would allow for a lower power density while covering a larger area than I could in CW mode for the same density.

Then again, I am only talking about a 1w diode. Perhaps in CW mode I'll end up needing few passes.

 

[Benm]

As long as your driver is good, doesnt have any overshoot when turning on and such, modulating it rapidly should not be a problem for such a diode.

Remember these 405 nm diodes are intended to be used like that, in their normal applications as blu-ray disc writers they switch in the megahertz range all the time.

I'm not overly sure about that driver circuit though, LM317's aren't really intended for such rapid changes. It may very well work, but could fail depending on the brand (many companies make 317s, all meet a minimum specification but are not otherwise identical).