Energy Density and Perceived Beam Brightness

[Laserman532]

it is all perspective.

brightness is perceived by the photo-topic response of the eye curve (which can vary slightly from person to person)

I dont like the power density vs. brightness comparison due to the variables involved

reason - a 1 mw laser and a 10 watt laser of the same wavelength will be perceived as the same brightness in the vacuum of space. Forward scatter, reverse scatter, particulate matter in the air, wavelength beam diameter, beam divergence...the variables in "this soup" are too vague and varied to be conclusive.

now...everybody cut my head off

[mccarrot]

But I think there is also a logarithm scale in the brightness thing, a 2W laser is not twice as bright as a 1W laser with similar beam specs

[Laserman532]

But I think there is also a logarithm scale in the brightness thing, a 2W laser is not twice as bright as a 1W laser with similar beam specs

perform the experiment in the vacuum of space

forward scatter, reverse scatter, viewing angle, divergence, diameter, wavelength, pulsed or cw,ambient light, particulate matter in the atmosphere, and so on and so on...your nice neat logarithmic scale quickly dissolves into either chaos or randomness of confusion.

[Kyle]

a 4mm focal lenght will give you a 1mm beam with divergence of 2-3mRad, but after a set of cylindirical lenses you get 1mRad with a 4mm beam.

Okay, thanks. A 4mm square beam at 1mRad isn't too bad, although it does seem very similar to drlava's achieved specs.

I would think that by equalizing and expanding the beam from a multimode diode you would actually hurt the beams perceived brightness since the energy density at any point in the beam will not be as high as it would be if the beam were allowed to remain a flat line profile. I've been thinking about the ideas being tossed around here regarding complex optics for these, but as I've said before the 1.6 mrad by .18 mrad that I'm getting right now with only an Aixiz glass lens assembly seems pretty damn good. Couple that with the increased energy density of the flat beam profile and I think that the perceived brightness should be quite nice. I don't think I'll need much better than that myself based on what I've seen in the way of beam shows and graphics. Of course lower energy density is better if you're audience scanning, but I never scan any spectators myself.

I see your point, and it does seem possible that the energy wouldn't be distributed very evenly using a cylindrical lens or prism pair system, etc. But for a simple lensing system such as the AixiZ lens assemblies, that certainly isn't a horrible beam. I'm just after those inexpensive, pencil-thin, super-bright blue beams. (Aren't we all?)

I plan on building my own projector within the next several months or year. I plan on using it just for my own entertainment, so I won't be doing any scanning near eye level. It seems that there are far too many variables when calculating a true MPE value to even risk it, IMO.

it is all perspective.

brightness is perceived by the photo-topic response of the eye curve (which can vary slightly from person to person)

I dont like the power density vs. brightness comparison due to the variables involved

reason - a 1 mw laser and a 10 watt laser of the same wavelength will be perceived as the same brightness in the vacuum of space. Forward scatter, reverse scatter, particulate matter in the air, wavelength beam diameter, beam divergence...the variables in "this soup" are too vague and varied to be conclusive.

now...everybody cut my head off

LOL, no need to cut your head off. I completely agree; I was just trying to find a relatively easy way of estimating brightness differences between lasers of different powers and beam sizes under similar atmospheric conditions. (amount of particulate, fog, haze, etc. in the air)

All in all I was just debating whether or not it would be worth it to build a drlava dual kit over the single diode kit. Given that the slow axis has the larger initial beam size, as mccarrot pointed out, I've discarded the idea of splitting the beam and recombining it via a PBS cube. In the end, I'll probably end up building a dual 445nm blue, not because I necessarily need the extra power, but primarily because of the larger, squarer beam that would be a better match for the other lasers in my proposed projector, especially an octo-red.

But I think there is also a logarithm scale in the brightness thing, a 2W laser is not twice as bright as a 1W laser with similar beam specs

Yes, brightness perception is definitely not linear, and as Pat also mentioned the response curve varies from person to person, eye to eye.

I don't remember where I first read it, but I've often heard that to achieve twice the apparent brightness with a given wavelength/beam specs, one needs to roughly quadruple the output power due to the average response curve of the human eye.

perform the experiment in the vacuum of space

forward scatter, reverse scatter, viewing angle, divergence, diameter, wavelength, pulsed or cw,ambient light, particulate matter in the atmosphere, and so on and so on...your nice neat logarithmic scale quickly dissolves into either chaos or randomness of confusion.

Exactly, from my admittedly limited understanding, space, or a true vacuum, rather, has no particulate matter, etc. so no scattering of the beam occurs, therefore no divergence and no visible beam. There are far too many variables to attempt to derive an absolute conclusion, but I'm just trying to make a somewhat educated assumption.

I guess the best thing to do would be acquire the two lasers I've described and place them side by side.

Thanks again to all for the continued discussion!

- Kyle

[kitatit]

Thanks for the heads up on those useful links guys.