Step 1: Understanding the Concept:
The production of laser light involves a specific sequence of physical processes within the lasing medium. This question asks for the correct chronological order of these processes.
Step 2: Detailed Explanation:
Let's trace the steps required to generate a laser beam:
1. (A) Pumping: The process must begin by supplying energy to the lasing medium. This is called pumping. The energy "pumps" the atoms or molecules from a lower energy state to a higher, excited energy state.
2. (B) Population Inversion: Pumping must be effective enough to create a special condition called population inversion. This is a non-equilibrium state where more atoms are in the higher excited state than in a lower energy state. This condition is essential for light amplification to occur.
3. (C) Stimulated Emission: Once population inversion is achieved, a single photon (from spontaneous emission, for example) with the correct energy can trigger an excited atom to de-excite and emit a second photon that is identical in phase, frequency, direction, and polarization. This is stimulated emission.
4. (D) Light Amplification: This initial stimulated emission starts a chain reaction. The two photons can stimulate more emissions, leading to four photons, then eight, and so on. This exponential increase in the number of identical photons, often enhanced by reflecting them back and forth through the medium with mirrors, results in Light Amplification. The entire process is "Light Amplification by Stimulated Emission of Radiation".
Step 3: Final Answer:
The logical and physical sequence of events is Pumping Population Inversion Stimulated Emission Light Amplification. Therefore, the correct order is (A), (B), (C), (D).