The spectroscopic and laser kinetic properties of the trivalent ytterbium ion in various solid-state media are reviewed. Contrasts between four- and quasi-three-level lasers (e.g., Nd:YAG versus Yb:YAG) are highlighted. Various architectures suitable for use in high-brightness high-power Yb:YAG lasers are examined, and achieved laser performance levels are summarized. The properties of alternative ytterbium-doped laser gain media are reviewed, and early laser results are cited.

Ytterbium solid-state lasers. The first decade

Ytterbium solid-state lasers: The first decade

Measurements are reported of the spectroscopic properties (absorption and emission spectra, stimulated-emission cross section, and radiative lifetime) of (YbxY1-x)3Al5O12 for nominal x values of 0.025, 0.05, 0.1, 0.2 and 0.3 at temperatures of 15–300 K. The emission cross sections of Yb:YAG with different Yb3+ concentrations were determined by use of the Fuchtbauer–Ladenburg formula and the reciprocity method. At low temperatures, the product (στ) of the effective stimulated-emission cross section and the radiative lifetime is greater than at room temperature for all concentrations. Product στ is nearly independent of Yb3+ concentration at a given temperature. These results will aid in the design of high-power thin disk lasers by use of highly doped Yb:YAG.

Dependence of the Yb 3+ emission cross section and lifetime on temperature and concentration in yttrium aluminum garnet

We have demonstrated the first stoichiometric Yb/sup 3+/ laser based on Yb/sub 3/A/sub 5/O/sub 12/ (YbAG). The laser operated in pulsed mode with a highest possible duty cycle of 85%. A slope efficiency of 27%, with respect to absorbed energy, was measured and the free-running lasing wavelength was 1048 nm for a 10% duty cycle. In a systematic analysis, measurements of spectroscopic and materials properties of (Yb/sub x/Y/sub 1-x/)/sub 3/Al/sub 5/O/sub 12/ for nominal x values of 0.05, 0.1, 0.15, 0.18, 0.25, 0.5, and 1 are reported. We also present a formalism to calculate the intrinsic fluorescence quantum efficiency (free of radiation trapping) and the fraction of reabsorbed light, based on measurements of the bulk and intrinsic emission lifetimes and the fractional thermal loading. Our best YbAG sample has an intrinsic lifetime of 0.664 ms at 94% quantum efficiency and a thermal conductivity at room temperature of 0.072 W/(cm-K).

Laser demonstration of Yb/sub 3/Al/sub 5/O/sub 12/ (YbAG) and materials properties of highly doped Yb:YAG

We present modeling studies of quasi-three-level laser oscillators, the validity of which was revealed by Ti:Al2O3-pumped Yb:YAG laser experiments, and these results are shown to be in excellent agreement with the theory. As much as 75% slope efficiency was obtained with a hemispherical laser cavity. Previous modeling calculations of laser performance have been valid only for certain special cases, restricting application to TEM00 Gaussian beam pumping and lasing profiles. This analysis may be applied to other longitudinally pumped quasi-three-level laser media in which the modes are not only TEM00 Gaussian beams but also other higher-order transverse modes, including the top-hat pumping profile that can be used to model transverse pumping schemes.

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Modeling of quasi-three-level lasers and operation of cw Yb:YAG lasers

A cw-pumped, repetitively Q-switched, InGaAs-diode-pumped Yb:YAG laser has been demonstrated at room temperature. An output energy of as much as 72 microJ/pulse at 1.03 microm with a pulse length as short as 11 ns (FWHM) was attained. No optical damage was observed despite the high saturation fluence (~10 J/cm(2)) of the Yb:YAG laser and the short pulse length.

G. Henein

Papers

Diode-pumped Q-switched Yb:YAG laser.