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Re: Why is 445nm a better wavelength for burning than 405nm

Who says it is?
 
Re: Why is 445nm a better wavelength for burning than 405nm

are you sure it is better :thinking:
 
Re: Why is 445nm a better wavelength for burning than 405nm

Umm, where have you heard this?
 
Re: Why is 445nm a better wavelength for burning than 405nm

Normally, smaller wavelength has more power or not?
 
Re: Why is 445nm a better wavelength for burning than 405nm

He's talking about photochemical damage - damage to the eye's chemistry, or reduction in colour perception as a result of it. Violet is absorbed better mW for mW (better for burning), but the blues are both more powerful, and the eye's chemicals are more affected by the blue shade, so exposure to the blue lasers are more likely to impair your colour vision. I think LSRFAQ has a good thread on this - something like "A plea for eye safety"?
 
Re: Why is 445nm a better wavelength for burning than 405nm

Ahh, I see where you went wrong.

"Exposure to intense blue light can cause photochemical retinal degeneration."

This doesn't mean it is good at burning. In simple terms, it means it is better at damaging your eyes sensitivity. Exposure to blue light can cause reduced sensitivity to the colour green especially which can take months to heal, among other things.

The "strongest peak at around 440nm" means that is the peak wavelength for photochemical retinal damage. Not burning.

If you want further information, do a bit of Googling.

EDIT: Beaten to it.
 
Re: Why is 445nm a better wavelength for burning than 405nm

Yeah smaller wavelength do have more burning power per photon but I don't know if a 200mW 405m, got more burning power that a 200mW 445nm or if the calculation with power/photon there already is included.

However in that case it says only that 440nm is the peak with the strongest reaction for the biological effect

peace
 
Re: Why is 445nm a better wavelength for burning than 405nm

right, Burnsy! a single 405nm photon has more power than a single 445nm photon. but when measuring optical power, in mW, you dont "count photons", you measure the power. so 100mW of 405nm will contain _less_ photons than 100mW of 445nm light.
405nm does burn better (paper and the like), even with the same optical power. thats because it is better absorbed than blue, for example (didnt have a blue on hand yet, though). i would guess white paper reflects off 90% of red and green light. with 405nm, obviously more is absorbed.. :-)

manuel
 
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Re: Why is 445nm a better wavelength for burning than 405nm

Krutz said:
right, Burnsy! a single 405nm photon has more power than a single 445nm photon. but when measuring optical power, in mW, you dont "count photons", you measure the power. so 100mW of 405nm will contain more photons than 100mW of 445nm light.
Click to expand...

It's the other way around. Shorter wavelengths have more power per photon, so a shorter wavelength has fewer photons per joule (1 watt X 1 second) of total emitted energy, not more.

Also 100mW is 100mW regardless of wavelength; the only difference in "burning power" is the difference in the proportion of the beam that is absorbed and converted to heat. Shorter wavelengths tend to be absorbed somewhat more efficiently than longer by most surfaces, but absorption vs wavelength is dependent on the properties of the surface, and not all surfaces absorb short wavelengths more efficiently than long ones.
 
Re: Why is 445nm a better wavelength for burning than 405nm

Yes, shorter wavelengths have less photons per mW.

Another factor, although not with just a raw beam, is that a shorter wavelength focuses to a smaller spot with a given lens.

Also. most of what you try to burn is organic, meaning it has a lot of carbon to carbon, and carbon to hydrogen bonds. Carbon in its graphite forms is black and absorbs visible light like crazy, but adsorbs UV more so. Carbon to hydrogen bonds, also in organics, for the most part transmit visible and adsorb UV like crazy. So as you get closer in wavelength to the 330-360 nm peak adsorption in many organics, you get a better disruption of the organic material.

I used to work with 351 and 365 nm lasers, and we could use thick sheets of ordinary acrylic and lexan as safety shields because of that C-H bond adsorbing UV like crazy.



Steve
 
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Re: Why is 445nm a better wavelength for burning than 405nm

heh you are right! I meant the same, and seemed to have confused myself.. edited. thanks for reading carefully! :-)

manuel
 
Re: Why is 445nm a better wavelength for burning than 405nm

bump

Peace,
dave
 
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