Low-Quantum-Defect Solid State Lasers: 2-, 3-, or 4-Level

摘要

The concept of three-level- and four-level-lasers was used early on to explain why it was easier to make the Nd3+ ion lase than the Cr2+ ion. Almost 50 years later, work on solid-state lasers has recently led to a quantitative definition of the concept. The new level parameters lambda(0) and lambda(1) defined here will provide an improved basis for comparing Nd3+, Cr2+, and other ions, e.g. Er3+, Yb3+, Ho3+, and Tm3+. lambda(0) and lambda(1) assign to a system of discrete energy levels a number, with a physical basis, that varies continuously between 2 and 4, in the same way that the Hausdorff and Renyi definitions yield non-integer dimensions for fractals. Together with the cross section, lifetime, etc., they help in the design of a laser by providing a basis for choosing the operating temperature, pump wave-length, and laser wavelength.