MadSci Network: Engineering

Re: Can you take 2 lasers, not visible, and cross them to get 1 point of light?

Date: Sun Sep 24 13:17:49 2000
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Engineering
ID: 969123069.Eg

Hello Jake,

That's a very interesting question!

Let's use the visible "additive" colors as an example - red, green, and 
blue. Each one has a different wavelength, but varying the amounts shown 
upon a surface of any two or more of them can produce any other color. 
Just as three pebbles thrown into a pond, each representing one of those 
colors, the wavefronts will at some point, meet and create another, very 
different ripple. This new ripple will have a different wavelength than 
any of the individual ripples; depending on how often (or the frequency at 
which) the individual ripples meet each other. So it is with light waves 
which intersect. At the point of intersection, the individual light rays 
will re-inforce, and then negate each other causing an entirely new 
frequency (wavelength) to be produced.

Laser beams are no different - except that they are a "pure" form of 
emmission, producing only one fundamental frequency or wavelength. 
Therefore, it certainly is possible to produce visible light from two or 
more invisible laser beams. What the eye will see is the new frequency 
produced by the reinforcement and negation of the intersecting beams.

A simple experiment with sound will prove this theory. If you send a high 
frequency, somewhere above the range of human hearing (like 30KHz), to one 
loudspeaker and another high frequency to second loadspeaker, by varying 
the frequency of one of them, a third audible tone will be produced, 
provided the two frequencies "beat" together within the audible range. Try 

Without going through the math, you should be able to take one Infrared 
laser (around 1000nm wavelength) and a Ultraviolet laser (<400nm) and 
produce something in the visible range. Try it! - BUT MAKE SURE YOU USE 
PROTECTIVE EYEWARE! Remember, what you can't see CAN hurt you! 

If you need any more help, you can contact me directly at:

Your not-so-mad scientist,


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