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405 vs 635 burning question

steve001

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First off, that's not what I asked. I asked why 405nm burns better than 635nm.

The question you asked is equivalent to asking why boiling water cooks something better (quicker), pasta for instance, than non boiling water, both the boiling water and the non boiling water contained molecules of H2O, but at different energy levels. Photons of violet light pack more energy per photon than red light photons same as boiling and non boiling water molecules. Violet photons transfer that energy to an object more effectively than red photons and it takes fewer violet photons to do so. All things being equal, spot size, output, surface color of object, between a violet laser and a red laser, violet light would still impart its energy quicker raising the temperature of the object it is shining on. The fact that violet light can be focused to a smaller spot size facilitates, but energy level is what really makes the difference.

Second, are UVB diodes available? Or something like 255nm? I don't know where UVA ends and UVB starts but just curious.
I don't know myself, but you can google for an answer.
 



Crazlaser

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The question you asked is equivalent to asking why boiling water cooks something better (quicker), pasta for instance, than non boiling water, both the boiling water and the non boiling water contained molecules of H2O, but at different energy levels. Photons of violet light pack more energy per photon than red light photons same as boiling and non boiling water molecules. Violet photons transfer that energy to an object more effectively than red photons and it takes fewer violet photons to do so. All things being equal, spot size, output, surface color of object, between a violet laser and a red laser, violet light would still impart its energy quicker raising the temperature of the object it is shining on. The fact that violet light can be focused to a smaller spot size facilitates, but energy level is what really makes the difference.

Um, not so sure about that. Boiling water cooks better because it has more kinetic energy than water at room temperature. I assume, since watts is a measure of energy, that two lasers that claim to emit the same amount of watts (energy) would actually do that. One wavelength may allow heat absorption to happen faster for reasons I don't know, however that doesn't mean it contains more energy.
 
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steve001

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Um, not so sure about that. Boiling water cooks better because it has more kinetic energy than water at room temperature. I assume, since watts is a measure of energy, that two lasers that claim to emit the same amount of watts (energy) would actually do that. One wavelength may allow heat absorption to happen faster for reasons I don't know, however that doesn't mean it contains more energy.
Spend sometime googling please.
 

bluestars

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Steve, I think you're confusing energy per photon (which is indeed wavelength dependent) with energy per unit time (aka power), which is independent of the wavelength. Photons have E=hf energy, where h is the Planck constant. A 405nm photon has Ea = hc/405e-9. A 635nm photon has Eb = hc/635e-9. When you cancel out, Ea/Eb = 635/405 = ~1.57. Doing the math, Ea = 4.9048e-19 J, Eb = 3.1283e-19 J. Any (honest) 200mW laser must emit 200mJ/s (0.2 J/s). If it's 405nm, that means it must emit 0.2 / Ea = 4.0776e17 photons per second. If it's 635nm, it must emit 0.2 / Ea = 6.3933e17 photons per second.

So a 635nm laser emits 1.57x as many photons per second as a 405nm laser of the same power, but they are 0.637x as powerful per photon, resulting in exactly the same average power emitted!

However, there are a number of other wavelength dependent effects. Firstly, all light that hits a target must be either absorbed, reflected, or transmitted. Most of the time, absorbed light is converted to heat. Many materials absorb more (reflect/transmit less) 405nm than they do 635nm. Secondly, the lower the wavelength (higher the frequency) of light, the better it can be focused. Google for "diffraction limited system" if you'd like to know more about this. It boils down to an equation like d = A/λ, where A is some constant derived from the material properties of your lenses and the like. So 405nm can be focused to a spot that is (you guessed it) 0.637x as large as that of 635nm. This is actually why Blu-Ray uses 405nm diodes! Finally, and this is a practical thing, not a physical property, the diodes available to hobbyists for 405nm are generally higher quality than those available for 635nm. The 405nm 16x Blu-Ray diodes are pretty amazing as far as beam characteristics go!
 
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diachi

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Steve, I think you're confusing energy per photon (which is indeed wavelength dependent) with energy per unit time (aka power), which is independent of the wavelength. Photons have E=hf energy, where h is the Planck constant. A 405nm photon has Ea = hc/405e-9. A 635nm photon has Eb = hc/635e-9. When you cancel out, Ea/Eb = 635/405 = ~1.57. Doing the math, Ea = 4.9048e-19 J, Eb = 3.1283e-19 J. Any (honest) 200mW laser must emit 200mJ/s (0.2 J/s). If it's 405nm, that means it must emit 0.2 / Ea = 4.0776e17 photons per second. If it's 635nm, it must emit 0.2 / Ea = 6.3933e17 photons per second.

So a 635nm laser emits 1.57x as many photons per second as a 405nm laser of the same power, but they are 0.637x as powerful per photon, resulting in exactly the same average power emitted!

However, there are a number of other wavelength dependent effects. Firstly, all light that hits a target must be either absorbed, reflected, or transmitted. Most of the time, absorbed light is converted to heat. Many materials absorb more (reflect/transmit less) 405nm than they do 635nm. Secondly, the lower the wavelength (higher the frequency) of light, the better it can be focused. Google for "diffraction limited system" if you'd like to know more about this. It boils down to an equation like d = A/λ, where A is some constant derived from the material properties of your lenses and the like. So 405nm can be focused to a spot that is (you guessed it) 0.637x as large as that of 635nm. This is actually why Blu-Ray uses 405nm diodes! Finally, and this is a practical thing, not a physical property, the diodes available to hobbyists for 405nm are generally higher quality than those available for 635nm. The 405nm 16x Blu-Ray diodes are pretty amazing as far as beam characteristics go!


Great post and explanation, +20. Bet me to the calculation. :p

We've been through this conversation before on this forum and it went exactly the same as this, I'm surprised Steve didn't see it, he would have been around then.

I think we can stop beating the dead horse now, hopefully? :D
 
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CurtisOliver

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Steve, I already explained when photonic energy matters. Diachi and bluestar are correct in this circumstance. The difference in photonic energy from 635 to 405 is so small that it is negligible. It is only if you compared a X-ray photon to radiowave photon would you see a difference. It is like firing 20 1kg balls at a wall compared to 5 4kg balls. (At the same velocity of course) The momentum is the same, but the stress on the wall in between photons is higher. With your concept it would be like starting with 1kg and 0.999...g balls and expecting there to be a difference. Like I said the difference would be negligible.
 
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blueasthesky

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I am not very versed when it comes to visibility of wavelengths... Would 240nm even be visible? And wouldn't it be amazing for burning?

That's okay :)

240nm is waaaaaaaaaaaaaaaaaaaaaaaaaaaaay below what we could observe. Think of how dim 405nm already is. We are talking almost 200nm shorter of a wavelength! Not only would it be invisible, but it could also give you pretty bad sunburns :eek:

-Alex
 

Lildutchboy7

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That's okay :)

240nm is waaaaaaaaaaaaaaaaaaaaaaaaaaaaay below what we could observe. Think of how dim 405nm already is. We are talking almost 200nm shorter of a wavelength! Not only would it be invisible, but it could also give you pretty bad sunburns :eek:

-Alex

Sooooooo.... A portable cancer/sunburn/death ray? This just sounds like something out of an 80s action hero movie:crackup:

seriously though, This would be a pretty unique laser to have:D
 

blueasthesky

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Sooooooo.... A portable cancer/sunburn/death ray? This just sounds like something out of an 80s action hero movie:crackup:

seriously though, This would be a pretty unique laser to have:D

Pretty much haha. Yes it would be :cool:

-Alex
 

diachi

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Um...

Is this site legit? Did some research for low UV powered diodes and found these? :eek:

UVTOP: deep UV LED at 240nm

-Alex

Those are LEDs, and very low output, as is common with UV LEDs, especially that far into the UV.

I am not very versed when it comes to visibility of wavelengths... Would 240nm even be visible? And wouldn't it be amazing for burning?


Not at all visible, visibility is completely lost not far below 400nm. They'll make a lot of things fluoresce though.

It'd be good for burning if you could get enough output power as the beam waist would be even smaller than 405nm (assuming same beam specs and absorption as 405nm). But getting optics for that wavelength would be expensive, never mind anywhere near enough output power to burn anything.

Not sure how much power you need for sunburn, but it's DNA damage that causes that, not actual heating of the tissue due to absorbed light.
 
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joeyss

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Let me tell you this that's getting into UVC you should be glad our ozone layer blocks uv-c

I have a 13 watt clear mercury lamp in an enclosure and you must wear googles (laser are fine) and cover your skin otherwise it will smell like a combination of dead and burnt skin. Even a few seconds of looking around without googles may result in bad arc eye. It makes styrofoam yellow in a day. These are not to be messed with if you have no idea they will make the blue light hazard from leds look like a joke. That's 254nm


wanna hear another fun thing about light 405 charges green GID stuff like the spray paint.

if i put my 808 laser which is 2 watts with no lens over a spot for 2 mins that area will be darker.

I wonder if 980 makes it faster?
 




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