What does amplification in lasers refer to?

Amplification in lasers refers to the process of photon stimulation of additional atoms. This process occurs in the gain medium of the laser, where an external energy source excites atoms, raising them to a higher energy state. When these excited atoms return to their ground state, they release photons. If these emitted photons collide with other excited atoms, they can stimulate the emission of more photons in a process called stimulated emission. This cascade of photon emissions is what leads to the amplification of light within the laser cavity, producing a coherent and powerful beam of light.

The other concepts mentioned, such as reducing beam divergence, absorption of energy by the medium, and loss of energy during transmission, are related to different aspects of laser operation but do not define amplification itself. Beam divergence pertains to the spread of the laser beam, energy absorption relates to how the gain medium is energized, and energy loss involves inefficiencies in the system. None of these accurately capture the essence of amplification as it pertains to the stimulated emission process critical to laser function.