Beam profile shape vs. capabilities of lasers

[julianthedragon]

I have a question about the two most powerful handheld lasers I own. I've looked a bit online but nothing has resolved the specific question I have in mind. Not sure if it's answerable in the way I'm presenting it here but figured it was worth a shot.

The two lasers are a 1.1W (measured) 1064nm* and 3.6W (measured) 465nm from JL.

The 1064 DPSS has a nearly gaussian beam profile and can focus to a pinpoint. The 465 uses one of those multiwatt blue diodes (NUBM07?), making it multimode and high divergence—it focuses down to a razor thin line a few mm across.

My area of concern is the differences in capability of the lasers brought on by their beam profile (dot vs line).

It's hard for me to experiment because a) not all variables like power, wavelength are constant and b) I don't have a lab at the moment and frankly I seldom find an ideal situation to use these lasers at all.

What I want to know: if other variables are held constant including exposure time and the material exposed, and we are given a dark material with moderate flammability, is there a difference in effect between striking it with a dot vs. a line? Is there, let's say, something about the line profile that starts a fire easier than a sharp point which is better suited for cutting? I'm questioning along those lines. I have lit paper on fire with the 465 and only ever been able to cut with 1064, but it's hard to say which of the many variables is responsible.

Hopefully someone with more laser cutting/burning experience is kind enough to enlighten me.

P.S. Happy New Year! Here is a beamshot of the 465 in fog.



*Out of respect for my eyes and the ridiculousness of owning these lasers, I take numerous safety precautions: batteries out until OD7 CE glasses on, tail cap safety switches, lens caps, IR indicator card on hand whenever operating the 1064nm, making sure there are no reflective surfaces and other people/animals nearby, etc.

 

[Eidetical]

It's all about energy density at the focal point and wavelength absorption. If the intensity of a line image from a multimode laser is high enough, the line shape may make things easier to ignite because it covers a bigger area on the target. Also, a target may not absorb a lot at 1064nm despite looking "dark".

 

[julianthedragon]

If the intensity of a line image from a multimode laser is high enough, the line shape may make things easier to ignite because it covers a bigger area on the target

Thanks. This confirms my intuition but is there any deeper physical explanation for why more area (at same power density)=easier to ignite? Less area covered is easier to cool down, to be sure. Just interested if there’s anything more to glean here.

Also, a target may not absorb a lot at 1064nm despite looking "dark".

You’re totally right. I almost mentioned something about this but felt like it was too much detail. I mean something that would absorb both wavelengths or a hypothetical third wavelength with dot and line profiles to test

 

[RedCowboy]

All laser beams diverge over distance but in addition the aggressive fast axis divergence of your blue multi mode means the rectangle shaped spot grows proportionally wider and wider over distance making it's spot cover more area which reduces it's ability to impart enough energy into a given area over a set duration of time.

As for burning vs. cutting you will notice when using a G2 lens on your 465nm up close, that a more tightly focused beam will cut a Popsicle stick without setting it on fire, but if you un-focus it a little you will get a flame kernel, this may seem opposite of what's expected but it's a time on target factor, the tight beam burns through too fast for the material to ignite.

Kind of like how moving air across metal cools it down faster, but get that air going really fast and it will melt the same metal.

So just like adsorption factors the material science can't be ignored.

 

[Encap]

Laser beam power density is Watts/cm squared at any given point at any along the beam. regardless of of wavelength or output power of the laser.

It is also important to understand/know/recognize that a laser beam has no temperature - there is no inherent "temperature" to a laser beam. Heat is the random motion of matter particles (atomic or molecular particles). A laser beam itself is not made of matter but of photons, which have no mass, thus a laser beam can have no temperature.
"Heat" depends upon/is caused by a laser beams energy being absorbed by a materials surface and turning light energy into heat energy.

You can learn more about what you are attempting to comprehend and how to properly calculate power density here: https://www.ophiropt.com/laser--measurement/laser-power-energy-meters/services/calculator

 

[julianthedragon]

Appreciate the responses everyone. I have a better understanding and some research to do

Will update when/if any new questions or curiosities arise