Maser: Microwave Amplification by the Stimulated Emission of Radiation
Laser: Light Amplification by the Stimulated Emission of Radiation
I had the distinct pleasure of taking Radiative Processes in Astrophysics from Dr. John Lacy at UT Austin.
John studied for his PhD under Charles Townes, co-inventor of the maser with Arthur Schawlow.
Of course, Einstein theorized such a device in 1917 and called the process "stimulated emission."
The men earned a patent in 1959 and used the maser to amplify radio signals and as an ultra sensitive detector for space research.
A year before, they generated papers about a visible laser, but did not pursue it beyond that.
Thanks to their groundwork, Theodore Maiman invented the ruby laser in 1960. Townes and Schawlow shared the Nobel Prize in 1964.
Light stimulates the electrons in atoms to move from lower energy to higher energy states. Upon returning to their original energy states, the atom releases energy in the form of a photon. Simplified illustrations I've seen showed one photon in; two photons out. Think of it as an efficient photo multiplier.
Minor list of everyday technologies using the laser:
CD players/ DVD players/ laser pointers (duh!)/ A/D digital communications/ light shows at concerts/ LASIK eye surgery/ dentistry/ kidney stone removal/ tumor surgery/ nuclear fusion/ computer printers/ science fiction/ construction (leveling)/ hair removal/ gun sight/ computer mouse/ auto manufacturing...
About.com: How a laser works
Laserfest.org: Celebrating 50 years of laser innovation
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