21. What was the active medium used in the first working laser ever constructed?
(a) A diamond block (b) Helium-neon gas (c) A ruby rod (d) Carbon dioxide gas
Answer
Answer : (c)
Explanation
Explanation : Theodore Maiman built the first working laser using a ruby rod while working at Hughes Research Laboratories in Malibu, California. It lased for the first time on May 16, 1960.