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How does quantum optics relate to lasers?

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Quantum optics is the study of the quantum interactions between light and matter. While quantum optics explores fundamental phenomena like photon entanglement and single-photon interference, its relationship to lasers is rooted in the physical process of stimulated emission.12

In 1917, Albert Einstein identified stimulated emission as a radiative transition where an incoming photon triggers an excited atom to emit a second, identical photon. This emitted photon shares the same energy, polarization, direction, and phase as the stimulating photon.2

The laser—an acronym for "light amplification by stimulated emission of radiation"—is a device built directly upon this quantum mechanical principle. Because stimulated emission produces light that is highly monochromatic, directional, and coherent, lasers have become essential tools in quantum optics for probing atomic structures and conducting sophisticated experiments that test the foundations of quantum mechanics.21