Old 03-27-2010, 07:49 PM #1
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Default Difference between CW and pulsed

Can someone briefly explain what the difference between pulsed and continuous wave is? I heard that pulsed is more powerful. But if you think about it, you get exposed for half as long... cuz if you were to burn wood. the wood gets hit by the IR for half as long which divides the exposure time to half so pulsed should be half as powerful right?


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Old 03-27-2010, 07:59 PM #2
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Default Re: Difference between CW and pulsed

You seem to have answered your own question...

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Old 03-27-2010, 08:05 PM #3
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Default Re: Difference between CW and pulsed

The only difference is that the beam is pulsed or continous, like you said. You are correct that pulsed lasers only hits the target half the time as CW lasers, so a 100mW CW laser would be more powerful than a 100mW pulsed laser.

The reason you heard that pulsed lasers are more "powerful" is that since they are only lasing half the time, the diode stays cool much longer, so that it can be boosted up without shortening the lifetime of the diode: a diode being run at 100mW CW is generating as much heat an degrading just as fast as the same diode run at, say, 150mW pulsed.
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Old 03-27-2010, 09:01 PM #4
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Default Re: Difference between CW and pulsed

Oh i get it thanks.
But wait. if a 100mW diode is 150mw pulsed at around say 1000 times a second, then it would be almost CW but still have 50% rest time. right?

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Old 03-27-2010, 09:21 PM #5
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Default Re: Difference between CW and pulsed

FYI- I was told that you cannot tell the diff. when looking at a laser dot,... but when you move it the CW laser appears as a line while the pulsed looks like a series of dashes.--HZ- but maybe not at 1000X per second.??
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Old 03-28-2010, 02:48 AM #6
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Default Re: Difference between CW and pulsed

When you are talking about gas lasers, pulsed gas lasers can run up into kW ranges, but if you somehow converted the laser to run CW, you might get maybe 10W out of it before it overheats.

Pulsed lasers are just good for keeping thermal stress down on applications that don't require CW lasers.
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Old 03-28-2010, 02:53 AM #7
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Default Re: Difference between CW and pulsed

Pulsed operation is varied in duration, "rest time", and intensity. It's not as simple as same power half the time. Most crystals respond better to higher power - they are more efficient. But higher CW power isn't always possible, so pulsing a diode at higher peak may actually give you more average power because of the increased crystal efficiency.

YAGs almost always give higher average power when pulsed. The laserscope can do either 10W CW or 40W (average) pulsed.

Some lasers can only be operated in pulsed mode such as copper vapor, excimer, nitrogen, ruby, and Ti:Sapphire.
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Old 03-28-2010, 04:38 PM #8
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Default Re: Difference between CW and pulsed

IMO the most important differences are in the laser's construction and principle of operation. Just to mention, pulsed lasers duty-cycle is in most cases much much smaller than half the time, and often we describe a pulsed laser with it's pulse energy, not pulse power. If you know the pulse energy in joules and frequency in Hz then you can get the average power in watts by simply multiplying energy by frequency

In context of laser cutting, especially metal cutting, type of operation is also important. You may get better results with pulsed laser that has 10W average power than CW laser of the same power, because in case of pulsed laser the single pulse power is many times higher than 10W and causes metal to sublimate, when 10W CW laser would only melt it. This is just an example of pulsed laser application. I think that we have something similar in case of excimer lasers that cuts tissue, however it's also not possible to make a CW excimer laser (this is another reason why we have pulsed lasers, mentioned before by Cyparagon - some kind of lasers just can't be made CW).
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