What critical discovery related to lasers was made by Einstein?

The principle of stimulated emission is fundamental to the operation of lasers. This concept, introduced by Albert Einstein in 1917, describes how an incoming photon can stimulate an excited atom to emit a second photon that is coherent with the first. This means that the emitted photon has the same phase, frequency, and direction as the stimulating photon, resulting in a highly organized and powerful beam of light.

In the context of lasers, this principle is crucial as it underlies the process of amplification that allows lasers to produce light that is both intense and precise. Without the understanding of stimulated emission, the development of laser technology would not have been possible, making this discovery pivotal not only in physics but also in various applications including telecommunications, medicine, and entertainment.

While other concepts attributed to Einstein, such as the theory of relativity, offer profound insights into the nature of space and time, they do not directly relate to the functioning of lasers. Similarly, the law of energy conservation is a fundamental principle of physics but does not specifically pertain to laser technology. Lastly, the particle-wave duality concept pertains to quantum mechanics and describes the dual nature of light and matter but does not specifically address how lasers operate. Thus, the principle of stimulated emission stands out as the