Which term describes the cascade effect caused by stimulated emission?

The term that describes the cascade effect caused by stimulated emission is "photon avalanche." This phenomenon occurs when a single photon stimulates an excited atom or molecule to emit another photon, which can in turn stimulate further emissions. This leads to a rapid and exponential increase in the number of photons, creating a cascade effect. In lasers, this process is crucial as it allows for the amplification of light, resulting in a coherent beam.

The other options do not accurately describe this specific process. For instance, "absorption cascade" refers to a process unique to absorption where multiple absorptions can occur but does not capture the amplification aspect of stimulated emission. "Frequency doubling" involves the nonlinear optical process where the frequency of light is doubled, resulting in light of a shorter wavelength, unrelated to the cascade of photons. "Energy settling" isn't a recognized term in this context, and it does not depict the active process of photon generation through stimulated emission.

Thus, "photon avalanche" aptly encapsulates the rapid, cascading production of photons essential for many opto-electronic applications, particularly in the function of lasers.