Rigrod laser-pumped-laser resonator model: I. Theoretical considerations

Abstract

Dilute laser materials whose ion doping is minimized are attractive because Auger up-conversion is minimized, substantially lower heat fractions result and transverse or longitudinal gain and heat deposition gradients are reduced. In addition, amplified spontaneous emission (ASE) effects are minimized as well. Lasers using dilute laser materials, however, tend to have lowered efficiencies due to the difficulty in obtaining efficient absorption in laser crystals of reasonable length. This is primarily because of the use of simple single or double-passed pump absorption schemes. While this difficulty may be overcome using multi-passed absorption pump beams, as has been successfully demonstrated in connection with the development of thin-disc lasers, higher absorption and efficiency are obtained with added complexity and cost. In this paper, we present an alternative method in which a dilute or thin absorbing laser material is placed intra-cavity to a pump laser resonator. With the absorbing laser crystal acting as an effective outcoupler, we find that the highest absorption and resonator extraction efficiencies are obtained with the most dilute or thin materials when resonator mirrors of near unity reflectivity are used. This counter-intuitive result is explained by a corresponding long photon lifetime inside the laser resonator, which effectively multi-passes the absorbing laser crystal, leading to a very high absorption efficiency.

Kinetics of Metastable Argon Optical Excitation and Gain in Ar/He Microplasmas

“…Using the data for pump intensity dependence in Figure b and for gain medium dimension in Figure , together with a geometric estimate for the beam-discharge overlap, we estimate an effective volume-averaged gain of ∼1 cm –1 and an overlap area of ∼0.2 mm 2 . A detailed fit of the Rigrod equation to the data, shown in Figure , determined the volume-averaged small-signal gain 1.05 cm –1 , beam-discharge overlap area 0.38 mm 2 , and gain medium transmission of the pump beam 0.34, consistent with the experimental estimates. The value of I sat was 16 W/cm 2 as noted above.…”

“…The observed output powers were consistent with expectations for this resonator and the estimated gain volume. This was confirmed by a conventional Rigrod analysis − of the resonator performance, based on output power measurements for six different output couplers with reflectivities 5% to 95%, for 8.7 W pump power, and 300 Torr. The output power was clearly maximized for a 40% reflective output mirror; this behavior is characteristic of a high-loss medium.…”

Intra-cavity pumped Yb:YAG thin-disk laser with 174% quantum defect

“…The wavelength is determined by the spectral gain, the linear spectral losses of the dichroic mirror, and the nonlinear spectral losses due to absorption in the intra-cavity pumped disk. Above threshold, the optimal output coupling of the intra-cavity pumped laser could be determined using the laser-pumpedlaser model developed by Brown [10]. At the threshold of the intra-cavity pumped laser, the saturation of its pump transition is negligible, and we can replace the nonlinear losses by linear ones.…”