ped
0
- Joined
- Nov 25, 2008
- Messages
- 4,889
- Points
- 113
Enough already.
Lets try and remain gentlemen, gentlemen.
Lets try and remain gentlemen, gentlemen.
LPF Donation via Stripe | LPF Donation - Other Methods
Links below open in new window
ArcticMyst Security by Avery
638nm as dim as a 405?
- Thread starter EpicHam
- Start date
- Joined
- Sep 12, 2007
- Messages
- 9,399
- Points
- 113
You seem like the kind of person that would insist on 650nm even with several tests from several people. I've got a test from the mitsubishi 300mW 638, but of course that won't be good enough, so I won't even bother digging it up.
Besides, YOU are the one claiming the datasheet is wrong. The burden of proof is on YOU, not me.
OOPS :shhh:
EpicHam
0
- Joined
- May 17, 2013
- Messages
- 971
- Points
- 0
grainde
0
- Joined
- Jan 29, 2012
- Messages
- 3,164
- Points
- 113
What ever CP you know as well as I do that the data sheet is incomplete. If you were any scientist worth their salt you'd have to admit that. You are the sad individual here...Oh and thanks for the neg rep, must have been some truth in my assertions that you really dont have a clue about physical chemistry. Who would have thought that atoms have band gaps..wow learnt something new.
Anyway sorry Ped had to at least reply. Im done.:beer:
Last edited:
EpicHam
0
- Joined
- May 17, 2013
- Messages
- 971
- Points
- 0
Take it somewhere else why don't you .
Last edited:
- Joined
- Sep 12, 2007
- Messages
- 9,399
- Points
- 113
Incomplete or not, there is no reason to assume >650nm comes out of a 638nm-rated diode.
The difference between you and me is that I welcome corrections.
You'll notice i even thanked you. "Holding your ground" is not the action of a scientist, it is the action of a politician.
- Joined
- Jul 8, 2012
- Messages
- 1,772
- Points
- 0
On the OP, nobody seems to have mentioned another reason why 445nm beams appear FAR brighter per mW than 638nm. The reason is an effect called Rayleigh scatter. This effect causes wavelengths closer to UV to basically bounce off of particles in the air and to bend in the air itself like a prism. 445nm lasers are quite close to UV and 638nm is quite far thus meaning the 445nm is scattered significantly more than the 638nm making it several times brighter. Then on top of the reduced scatter effect your eyes are less sensitive to 638nm than they are to 445nm. A wavelength comparison like the OP used is actually not supposed to compare beams but instead to compare the dots. That way you are comparing purely the eye's sensitivity to the wavelength itself.
EpicHam
0
- Joined
- May 17, 2013
- Messages
- 971
- Points
- 0
Are you sure??
Because Rayleigh scattering has mainly to do with the scattering of EM when the particles are many times smaller than the wavelength.
However the main reason why we can see the laser beam is because of diffuse reflection from the dust particles...
Shouldn't Mie scattering be more apro?
Besides , we are just talking about a few kilometres , now I'm no expert. But the way I see it. The absorption spectrum and reflectivity of particulates has a much more profound effect .
Last edited:
- Joined
- Jul 8, 2012
- Messages
- 1,772
- Points
- 0
Think about it, if it was caused by the light bouncing off of dust wouldn't you see 638nm and 445nm beams in a ratio nearly identical to what you would see when the dots hit a wall? Because 638nm is much less effected by Rayleigh scatter than 445nm it passes through the air much less impeded and creates beams significantly dimmer than it would in comparison to dot brightness.
A note Rayleigh vs Mie, actually Rayleigh is the right specific type. Mie scatter is when all the wavelengths are effected equally because the particles involved are near in size to the wavelengths of light involved. Rayleigh scatter specifically effects different wavelengths differently due to the particles involved being smaller than the wavelengths involves, as is the case with lasers in air. Talking about air we are looking at micrometer sized particles where lasers are nanometer sized wavelengths which means we are indeed looking at relationships where the scatter is caused by the particles being much smaller than the wavelength.
A note Rayleigh vs Mie, actually Rayleigh is the right specific type. Mie scatter is when all the wavelengths are effected equally because the particles involved are near in size to the wavelengths of light involved. Rayleigh scatter specifically effects different wavelengths differently due to the particles involved being smaller than the wavelengths involves, as is the case with lasers in air. Talking about air we are looking at micrometer sized particles where lasers are nanometer sized wavelengths which means we are indeed looking at relationships where the scatter is caused by the particles being much smaller than the wavelength.
Last edited:
EpicHam
0
- Joined
- May 17, 2013
- Messages
- 971
- Points
- 0
Maybe because dust has a higher absorption for light in the 638 spectrum?
I see your point but its a bit hard to imagine the effects of Rayleigh scattering coming into effect as just a few metres
- Joined
- Jul 8, 2012
- Messages
- 1,772
- Points
- 0
Dust is typically organic material and organic material absorbs light near UV better than approaching IR so its quite the opposite. This is also the reason 1W 405/445nm lasers burn more than the 1W 630nm lasers by a respectable amount. If all the lasers were single mode the 405nm would burn just slightly better than the 445nm and a descent amount better than 638nm at the same output.
- Joined
- Aug 7, 2010
- Messages
- 2,086
- Points
- 0
Forget about dust. The "bluer" the wavelength, the bigger the scattering.
Red scatter little, and our eye cannot perceive it well, so overall it seems dimmer than other colors.
Do you ever had a LPC or any dvd burner laser, ham? You could easily tell by comparing...
Red scatter little, and our eye cannot perceive it well, so overall it seems dimmer than other colors.
Do you ever had a LPC or any dvd burner laser, ham? You could easily tell by comparing...
Last edited:
- Joined
- Jul 8, 2012
- Messages
- 1,772
- Points
- 0
The scattering you see is caused by Rayleigh scatter combined with larger dust particles in the air. Red(638nm) lasers are only slightly dimmer to our vision than blue(445nm) lasers so most of the reason the beams are dimmer on red lasers is because of the reduced scatter effect.
I love 1W+ 638nm lasers. They are actually powerful enough to make respectable beams at night.
I love 1W+ 638nm lasers. They are actually powerful enough to make respectable beams at night.
EpicHam
0
- Joined
- May 17, 2013
- Messages
- 971
- Points
- 0
Well no.... this is my first "red" laser :shhh:
Ahhh...
So the oscillating electric field of a light wave acts on the charges within the gaseous molecules and the particulates within the atmosphere, causing them to move at the same frequency.
Thus the irradiated mass becomes a small radiating dipole and thus we get the signature light beam .
That is the dominant reason that attributes to the illuminance difference ,2nd by the human visual sensitivity spectrum , 3rd the divergence of the laser , 4th the particulate characteristics.
Yes?
- Joined
- Jul 8, 2012
- Messages
- 1,772
- Points
- 0
Yes and unfortunately this effect also causes 445nm beams to diverge even faster than the optics would normally cause them to. I can hit significantly further ranges with a 638nm laser than I can with a 445nm laser even when the 638nm laser is less than half the output and has a higher divergence. This effect is also the reason we are able to tiny 5mW pointers and they can travel for miles with good optics. A 445nm laser at the same output and divergence would totally fail in comparison. Green(520/532nm) lasers are a sort of middle ground so they scatter some but then visual sensitivity is extremely high(many times more sensitive than 445nm or 638nm) at that wavelength so they can make visible beams for the least amount of output. The availability of super high powered green lasers is the main reason 445nm lasers are still kings of beam making.
The scattering effect is the top reason they are brighter. Visual sensitivity only plays a small part but it does further reduce the perceived brightness of red lasers.
The scattering effect is the top reason they are brighter. Visual sensitivity only plays a small part but it does further reduce the perceived brightness of red lasers.
- Joined
- Aug 7, 2010
- Messages
- 2,086
- Points
- 0
@ApexProxy
Didn't knew that (about the 445 lower range)... +1 for you sir.
Do you think a prism pair or corrective optics (fast axis collimator) would be more of a waste on a 445 build? I have some optics and I'm still thinking of a setup... :eg:
Didn't knew that (about the 445 lower range)... +1 for you sir.
Do you think a prism pair or corrective optics (fast axis collimator) would be more of a waste on a 445 build? I have some optics and I'm still thinking of a setup... :eg:
