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Thread: Why can't other light sources be used to get tight (laser like) beams?

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    Default Why can't other light sources be used to get tight (laser like) beams?

    EDIT: The way some of the members here have desperately tried to identify my location and nationality for whatever reason they believed was needed for by asking an admin to check my profile logs and researching me by the content of my posts has been very creepy and unnecessary. So bye.
    Last edited by dream; 04-28-2016 at 16:27.

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    There is a bit of truth to that but, in general, the laser is not going to diverge the way another light source would and therefore the energy is going to remain more focused. There have been a number of recent non laser lights that are getting to look more and more like lasers but, no where near the power density of the laser. Look at the Sharpy for example. You can get it narrow but, not like a laser. I have a couple American DJ Vizi beam Hybrid 2R moving head lights that with a gobo with a small circle combined with the 8 facet prism and a green dichro look to an audience very much "like" a laser turned way down but, can't possibly match the brightness. First you're blocking a lot of the power of the 2R bulb by using a pin hole sized gobo, then dividing it by 8.

    I often use them to "scan" and audience with the real lasers being overhead since it's almost what a laser, set up for US legal audience scanning, might look like. Dim, diverged but still a fairly tight beam at close range - say 75 feet or so.

    There are also things such as the Emulaser in Beyond that coupled with a bright video projector with a very high contrast ratio looks damn near like a laser as well.

    But in the end, I don't think a non-laser light source is ever going to give you the intensity of a laser just by using optics to focus it.

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    The laser is effectively a point source with a far smaller source size then can ever be attained with a filament or led. Every other source effectively radiates as a large radius sphere. Because the laser has gain along what could be visualized as a small cylinder along the beam axis, it permits the creation of tight bundles of photons.

    Nothing else gets even close without huge losses when you clip out only the portion of the light you need to create a laser like beam.

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    Optically i recon there is a fair chance of acheiving a tight and compact beam, but the size of the whole thing would be massive compaired to laser. Remember that Lasers are meshured by the actual output, but other lightsources like bulbs and LED, are meshured by consumption. With a 100Watt bulb - more than 90% are waisted in heat, optics needed waist even more due to size and the requrement for full specter transparency. Effect out might be a 1 watt or so. (Not very scientific answer, but you get the idea).

    Regardless that, i have been puzzeling with the idea of using the 100W LED chips to build a PINspot as tight as possible. They are so bright, and it should be doable.
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    The original laser Emulator made by Lightwave Research back in the 90's used a 650watt short arc Xenon lamp with special optics to focus a beam through a literal pin hole in a brass disk to make the simulated laser beam, This then passed through a color wheel and large set of galvos for scanning. Super inefficient, but ti worked back in the day. Now you have the Elation Sniper 2R which uses s specially designed lamp/reflector combo to produce the same results in a slightly smaller package. It would be difficult to achieve the same results using LEDs, since the light emitting surface area is much larger for the power required to make a bright beam.

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    A typical high power led has a emitting width 500-2000X that of a diode laser. So, If you collimate the led with the same FL lens as used on a laser diode the spot on the wall will be 500-2000 times bigger. If you want to shrink the spot on the wall to the size of a diode laser the collimating lens would have to be 500-2000 times bigger in diameter to catch the light coming of the LED. So, the starting beam size would be 500-2000 times the size of a laser diode.

    Its a physical invariant.

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    Off topic a bit.

    If I really wanted to make an Emulator or Pin Spot, I'd use what they replaced the 650 Watt Xenon with in later models. A 175 or 400 watt Cermax Xenon lamp with integral reflector. I'm really fond of Cermax sources and their Ushio and GE clones. If you buy one, get the parabolic reflector, the ellipticals will work, but the parabolic has the best collimation.

    Once I had two 1000 watt parabolic Cermax's for a project, and wow, what brightness!

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    If anyone is interested I have 4 of those emulators in road cases with a controller….

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    Lightbulb

    Quote Originally Posted by dream View Post
    ..Laser light is coherent. Okay, but why is it a big deal......why is this a "thing" for tight beams for entertainment/art use (since not all of our beams are coherent) How is that exclusive to lasers though? The tight beam is created by lenses, not the laser.
    The 'difference' is due to the 'core-physics' of how LASER-light is generated.. Remember: LASER = Light Amplification by Stimulated Emission of Radiation.. Sure, in 'incandescent sources' (arcs, either open-air or sealed tube (Xenon, Krypton) and metal-halides / sodium-vapors, 'standard light-bulbs', fluorescents, etc, etc..) - even LEDs - you have the 'SER-part' - 'stimulated emission of radiation' (energy, producing photons..) BUT, you don't have the *Amplification*, and BY 'SER' aspect happening. This 'amplifier' is aka the 'Resonator', which forces the light to re-collide with other photons being produced, and 'stimulate' others to be produced - "Light amplification"..

    ..And, this Resonator, can be the mirror-like surfaces of a LOT of crazy-things, from semiconductor-chips, to superheated-gas fronts in Space, to.. the 'gut-walls (iirc..) of a bacterium'.. (!) Typically, though, yes, it's two mirrors, aligned in-parallel (or, other pathway-formations, a 'Z', 'L', U, M, V, etc or even a 'ring'..) and one is 'Totally reflective', and the other is 'partial' (but, near-total, like 99% or better..) There are plenty of 'exceptions'/ variants, etc, all too-much to discuss all, here.. But, point is - A *resonator* is what creates this 'phenomenon' of amplification, that just does not exist in a non-Laser source..

    ..Now, that resonating 'lasing-process' is also what makes Laser-light 'exclusive', because then all the photons, then 'stick together' (become 'coherent', or, in-phase with each other..) and stay-that way, regardless if they are 'going wide' (ie, from the junction of a semiconductor-resonator (diode), or, 'going long' (ie: in the beam of a HeNe or othe gas-laser..) But, they are, indeed, 'staying on a PATH', rather than going all willy-nilly, like light from a light-bulb (even a 'focused one', like a moving-head light lamp..) or the Sun, etc..

    ..And, in the case of your idea that 'the tight beam is created by lenses, not the laser', well you really only think that because you've apparently not had much experience with a Gas-laser.. Yes, diode laser-light, when 'collimated' (like being 'optically funneled'..) produced a 'beam', but.. That does-not mean a diode's Laser-light isn't 'coherent'..

    ..SO, that-said, when you try and 'simulate a laser beam', with a high-intensity light / video-pj, etc, etc, all you're really doing is 'cropping' the willy-nilly light, via mirrors / prisms / apertures, whatever, and directing / focusing (collimating) it to 'sim' that directionality.. But, due to this fundamental difference between *how* the light is produced, to begin with, you will just never approach a Lasers' intensity (due to the amplification), purity (due to the inherent-monochromacity), and coherence-length, THAT is 'why it's a thing' for entertainment / art - and - even when you 'chop it up' / bake it, ie: thru a Lumia-wheel / diffraction-grating, etc..

    Hope that helps (not worsens..
    j
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    Lightbulb Google "spacial coherence"

    All good replies so far, but I'm surprised no one has mentioned spacial coherence yet. True, for modern multi-mode diodes, the coherence length is measured in millimeters, but for a helium-neon laser or well-controlled DPSS green it can be measured in feet, and sometimes in yards.

    Plus, even after the spacial coherence is lost (mainly due to the fact that even though we say a laser is mono-chromatic, tiny quantum fluctuations mean that there are many wavelengths lasing in a narrow band of a few megahertz on even the tightest mode-locked lasers), the waves are nonetheless far closer to being absolutely parallel (and in-step, as it were) than they would be from any other light source.

    Finally, the fact that the wavelength is very precise (apart from the slight variation described above) means that any optic placed in the beam path will refract the beam equally with no abberation.

    Put all this together and you end up with a beam that starts out very near to perfectly parallel*, and is far easier to keep that way (using lenses, for example) compared to a standard light source.

    Adam

    * Diode emitters are the exception to this rule. The beam from a laser diode is normally generated in a very tiny space, and the initial beam divergence is quite poor. However, as others have mentioned above, because it is so close to a theoretical point source, a simple collimating lens can bring the beam back to being nearly perfectly parallel. Plus, since the lens is VERY close to the emitter, it can be within the spacial coherence length of the diode, making the lens that much more efficient.
    Last edited by buffo; 03-26-2015 at 15:33. Reason: typo

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