Summary

This 1964 monograph by Nobel laureate Alexander Prokhorov presents the foundational theory and experimental principles of laser operation, focusing on the quantum-electrodynamic processes that enable stimulated emission and population inversion. The book systematically derives the conditions for laser oscillation, including threshold gain, resonator modes, and the role of active media, with particular emphasis on solid-state and gas lasers. Prokhorov’s central thesis is that coherent light amplification arises from precise control of atomic energy-level transitions within a resonant cavity, a concept he helped pioneer alongside Nikolay Basov and Charles Townes.

The work details key mechanisms such as three-level and four-level pumping schemes, the linewidth of laser emission, and the dynamics of Q-switching. Readers gain a rigorous understanding of how population inversion is achieved and maintained, the mathematical description of cavity modes, and the practical constraints on laser efficiency. Prokhorov also discusses early applications in spectroscopy and metrology, grounding theoretical insights in experimental reality. The book remains a classic reference for the physical principles underlying laser technology.

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Key concepts

Stimulated emission — The process by which an incident photon triggers an excited atom to emit a second identical photon, enabling light amplification.
Population inversion — A non-equilibrium state where more atoms occupy a higher energy level than a lower one, necessary for laser gain.
Resonator modes — The discrete spatial and frequency patterns of electromagnetic fields that can exist stably within an optical cavity.
Q-switching — A technique to produce short, high-power laser pulses by temporarily reducing the cavity’s quality factor to store energy, then releasing it rapidly.
Three-level laser — A laser scheme where the active medium uses three energy levels, with pumping from the ground state to a short-lived upper level, followed by decay to a metastable state.
Threshold condition — The minimum population inversion required for laser oscillation, determined by balancing gain against cavity losses.