rwolff
Enlightened
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One last thing, I have asked many people about this and got mixed responses, is a white laser possible??
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Short answer: No (the "white laser" referred to earlier is actually a mix of red and yellow-green).
Long answer: Lasers have ridiculously low dispersion (if someone were to shine a laser on the moon, the "spot" would be about 1/4 mile across) because they use monochromatic (all one wavelength - that's why people talk about the wavelength in addition to the colour) coherent (all the waves are in phase) light. White light involves light of all colours, and you can't get coherent light if you've got multiple wavelengths (due to the different wavelengths, they quickly get out of phase).
The name "laser" comes from "(L)ight (A)mplification by (S)timulated (E)mission of (R)adiation" - your lasing medium (gas, ruby rod, or diode) receives energy (electrical or photoflash) to put the atoms in a high-energy state. Some will fall back to a low-energy state, giving off a photon in the process (wavelength determined by energy difference of the 2 states). Mirrors (parallel cleaved surfaces in a laser diode) reflect the light back and forth inside the lasing medium. If a photon hits an "excited" atom, it is absorbed and two photons are emitted as the atom drops to the low-energy state - this is the "stimulated emission" in the name. Both of these photons will be identical in wavelength, polarization, and phase.
Here's an analogy: think of "wavelength" as the length of a person's stride, "direction of travel" as which direction they're walking, and "phase" as how far into their stride they are (treat "right foot hits ground" as the start).
White light: Bunch of people (ranging from midgets to basketball players) walking in the same general direction.
Monochromatic non-coherent light (like a normal LED): Bunch of clones (i.e. everyone the same height) walking in the same general direction.
Laser beam: An army of clones marching in step.
One last thing, I have asked many people about this and got mixed responses, is a white laser possible??
[/ QUOTE ]
Short answer: No (the "white laser" referred to earlier is actually a mix of red and yellow-green).
Long answer: Lasers have ridiculously low dispersion (if someone were to shine a laser on the moon, the "spot" would be about 1/4 mile across) because they use monochromatic (all one wavelength - that's why people talk about the wavelength in addition to the colour) coherent (all the waves are in phase) light. White light involves light of all colours, and you can't get coherent light if you've got multiple wavelengths (due to the different wavelengths, they quickly get out of phase).
The name "laser" comes from "(L)ight (A)mplification by (S)timulated (E)mission of (R)adiation" - your lasing medium (gas, ruby rod, or diode) receives energy (electrical or photoflash) to put the atoms in a high-energy state. Some will fall back to a low-energy state, giving off a photon in the process (wavelength determined by energy difference of the 2 states). Mirrors (parallel cleaved surfaces in a laser diode) reflect the light back and forth inside the lasing medium. If a photon hits an "excited" atom, it is absorbed and two photons are emitted as the atom drops to the low-energy state - this is the "stimulated emission" in the name. Both of these photons will be identical in wavelength, polarization, and phase.
Here's an analogy: think of "wavelength" as the length of a person's stride, "direction of travel" as which direction they're walking, and "phase" as how far into their stride they are (treat "right foot hits ground" as the start).
White light: Bunch of people (ranging from midgets to basketball players) walking in the same general direction.
Monochromatic non-coherent light (like a normal LED): Bunch of clones (i.e. everyone the same height) walking in the same general direction.
Laser beam: An army of clones marching in step.
