Parasitic Suppression in Large Aperture Nd:Glass Disk Laser Amplifiers

Abstract

Threshold conditions for bulk and surface parasitic oscillations, which may limit energy storage in large aperture Nd:glass disk lasers, have been developed as a function of material parameters. An expression describing the energy storage distribution within a disk was used to determine the mode that will be most limiting for a particular disk design. Additional modes that may be limiting in special cases were identified and their effects evaluated. These results are useful in developing disk laser designs that minimize parasitic effects.

Potential of high-average-power solid state lasers

“…The stimulated-emission cross section of the laser transition determines the maximum stored energy density £ d achievable in a laser plate, con sistent with the constraint imposed by amplified spontaneous emission. Calculations 3 and design experience 42 both show that the product of the plate-averaged small-signal gain coefficient, a = IT, AN, and the effective dimension of the plate, nl", should be constrained to a value less than 3 (that is, ant = a L ANnS" < 3) in an energystorage laser. Here AN is the plate-averaged population inversion density, and £ d = IwAN.…”

“…In designing a high-average-power solid state laser there are, of course, design constraints other than thermal constraints. For example, if the me dium is to be used in an energy-storage mode, the well-known parasitic-loss constraints 42 developed for large solid state fusion lasers must be applied. Thus the product of the plate-averaged gain coef ficient 5, the index of refraction n, and the length j?…”

Design, development and performance characteristics of a large aperture disc amplifier for high power Nd: Glass laser chain

“…While thick discs (typically ∼ 40 mm) were preferred for larger gain, the thinner discs (typically ∼ 15 mm) were required to minimize the various losses as described above for the discs of dimensions of ∼ 100 × 200 mm. The laser discs were also cladded to minimize the parasitic oscillations using a glass material of matching refractive index and high absorption at 1054 nm (Glaze et al 1974). Figure 1a shows an optical scheme of the disc amplifier consisting of three Nd: phosphate glass, elliptical shaped discs (LHG-8 from Hoya, Japan) kept at Brewster angle, mounted in aluminum cassettes in a zigzag configuration.…”

High-power pulsed lasers

“…Similar considerations occur within the individual amplifier. 45 " 47 The stored gain within the amplifier is such that if internal reflectivity is not controlled, the amplifier will break into oscillation internally and the gain level will be clamped at the oscillator threshold condition inside the disk, G 2 R| Ri "i. 1 Examples of modes are shown in Fig.…”