30 mw green laser vs. 50 mw blue/violet laser

I recently picked up a green laser that was advertised as being 30 mw. It's bright and the beam is easily visible in low light.

I then picked up a blue/violet laser that was advertised as being 50 mw. That laser is nowhere near as bright as the green laser and the beam isn't visible even in a dark room.

So is the blue/violet laser really 50 mw? If is was wouldn't it be brighter than the green laser? Or is it not that simple?

P.S. I've got a Ph.D. In physics, but I'm a novice with lasers?

Hi JB, Welcome to the forum!

http://laserpointerforums.com/f44/good-know-laser-term-guide-newbies-58951.html

Go down to wavelength and take a look.

Basically our eyes have a specific spectrum that we consider visible. At the ends of the spectrum, things are a bell curve in that we slowly stop being able to see wavelengths above and below a certain amount.

Ultra Violet, and infared are Just beyond our spectrum, which means deep red and very violet are the colors that start to fade for us.... Which is why black lights seem so confusing - they're not 'bright' but when reflected off of a white shirt, it seems bright then.

Green is near the middle of our detective range, which means it will seem brighter with less intensity. Infared lasers are dangerous for this very reason; we can't see them but they are just as intense as regular colored lasers

Thanks for the reply! I was wondering if some of the light of the blue/violet laser was "off" towards the ultra violet and beyond my vision.

The spot from the blue/violet laser looks violet on some surfaces and blue on others, for instance on white paper. When the spot is blue, it looks much brighter than when it's violet. So that seems to indicate that the blue/violet laser is acting the same way as the black light example.

So my next question is, if I wanted a blue laser with a beam I could see in low light, what kind of blue laser should I get? And the same question goes for a red laser. Is that even possible (and not too expensive, say less than $100)?

Well o-like has a 400mw 405 for around $95 that should have a nice beam and I have one of their waterproof 200mw red and sometimes I can see the beam on it too.

405 is getting more towards the uv end of the spectrum... Personally I would recommend looking for a blue laser at 445/447nm wavelength. Looks more blue than 405, and would be a little more visible as well.

JBElliott said:

Thanks for the reply! I was wondering if some of the light of the blue/violet laser was "off" towards the ultra violet and beyond my vision.

The spot from the blue/violet laser looks violet on some surfaces and blue on others, for instance on white paper. When the spot is blue, it looks much brighter than when it's violet. So that seems to indicate that the blue/violet laser is acting the same way as the black light example.

So my next question is, if I wanted a blue laser with a beam I could see in low light, what kind of blue laser should I get? And the same question goes for a red laser. Is that even possible (and not too expensive, say less than $100)?

Click to expand...

Hey JBElliott,

You mention "some of the light... off towards the UV..." Since lasers are (mostly) mono-chromatic by definition the light output of your 405nm laser is only the single color of that wavelength. So you are seeing all of the light that is being output.

The issue is that our eyes have a non-linear response curve to different wavelengths/colors of light:

Spectral sensitivity - Wikipedia, the free encyclopedia

and

1988 CIE Photopic Luminous Efficiency Function

In well lit conditions we see in with photopic vision which has a peak sensitivity at around 555nm (GREEN) and tapers off from there in a bell curve as enigmahack mentioned.

By using the chart posted above it can be calculated that a green 532nm laser will appear ~190 times brighter to your eyes than a 405nm laser at the same power level. This effect is what makes IR/NIR lasers so dangerous.. a 532nm laser is around 60,000 times brighter in appearance than a 780nm CD-R diode running at the same power level.

You mention that the spot looks violet on some surfaces and blue on others. This is due to florescence. Generally when florescence occurs, radiation is absorbed by the object and radiated at a longer wavelength. different florescent objects will emit different wavelengths/colors of light. The blue florescence that you are seeing is likely due to UV brighteners which are present in most paper and laundry detergents.. which is why your socks will glow quite intensely when your 405nm pen is shinning on them. The reason it looks brighter is because the emitted florescence is shifted into a longer wavelength which your eyes are more sensitive too. And yes, this is the same effect as a black light. Blue is the most common.. but try shining that laser on more stuff and you will see different colors.

To see the beam, you need a laser that your eye is more sensitive too, but with a short enough wavelength to cause significant Rayleigh scattering. 445nm and 532nm will work very well for this. A red laser has a longer wavelength and doesn't cause as much Rayleigh scattering.. so the beam is not nearly as visible as blue.. and especially green. While your 405nm has a short enough wavelength to cause Rayleigh scattering.. you just can't see it well enough at the commonly available power levels. It's easy to calculate that you would need approximately 1W of 405nm laser light to match the beam visibility of a 5mw 532nm green pen pointer.

Rayleigh scattering - Wikipedia, the free encyclopedia

With all this said.. your cheapest option for badass beam viewing is 532nm green.. followed by 445nm... Otherwise get a fog machine :beer:

I hope this helps.