What would it take to make a white laser?

Question

Red, then Green, now Blue....could one be made by collimating all those three colors, kind of like yellow lasers are made with red and green diodes?
Might there be some theoretical way to make a single white laser diode, kind of like the recent white LED breakthrough?

Answer 1

Actually, phase coherency is a side-effect that happens to be useful, but is not essential to lasers (though it is often desirable).

The basic idea behind a laser is: Light Amplification by Stimulated Emission of Radiation. It is possible for a medium to "lase" at several frequencies simultaneously - that is, to give off light at multiple frequencies when suitably pumped and stimulated. (Think of tunable dye lasers.)

However, for the resulting light to be "white", both the frequencies and their relative amplitudes have to be right.

Furthermore, most (but not all) lasers need a "resonant cavity" (this is where the mirrors come in). So not only must the lasing medium be just right, so must the cavity.

With so many constraints, designing and building a true white-light laser may well be impossible, and even if possible, is going to be very hard. Since hard means expensive, and there is little advantage to a white laser, I doubt there will be much effort in this area.

On the other hand, if what you want is a phony "white" laser - a beam that combines the output of three different lasers into one beam - that is done all the time.

Most modern fiber optic cables used for long distances are "wavelength-division multiplexed" which means multiple lasers pump their light and data into the same fiber. What come out the end is a mixture, which then gets separated. Nobody actually cares about the resulting color, so the frequencies and amplitudes aren't chosen to make "white", but they could be if the need arose.

For WDM, check out:
http://en.wikipedia.org/wiki/Wavelength-division_multiplexing

Answer 2

Well..... Since white light is, by definition, a mixture of all colors it would be something of a trick to maintain any kind of phase coherency (which is what lasers are all about).

Doug

Answer 3

you will need what is called 'plasma'. plasma is the fourth category of matter. there is solid, liquid, gas, and finally plasma. it is the hottest and brightest matter in the universe.

Answer 4

how are you going ot make it white, if white doessnt doo anything