What was the active medium used in the first working laser ever constructed?
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A diamond block
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Helium-neon gas
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A ruby rod
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Carbon dioxide gas
C
Correct answer
Explanation
The first working laser, built by Theodore Maiman in 1960, used a synthetic ruby crystal as the lasing medium. The ruby rod was pumped by a flash lamp to produce the laser beam. Helium-neon and carbon dioxide lasers came later, and while diamond can lase, it wasn't used in the first laser.