Saturation of 1.064 μm absorption in Cr,Ca:Y3Al5O12 crystals

Abstract

Saturation absorption experiments are conducted on the title compound at 1.064 μm with laser light propagating along both the [001] and [111] crystallographic axes. Rotation of the crystals about these axes during the experiments reveals that the transmission of the polarized 1.064 μm radiation is highly anisotropic in the saturation regime. The details of the anisotropy and saturation curves are explained using a simple model of subsets of optical centers along with a relevant set of rate equations. The ground and excited-state absorption cross sections at 1.064 μm are calculated to be σgs=5.7(±2)×10−18 cm2 and σes=8(±2)×10−19 cm2, respectively, and the optimum crystallographic orientation for utilization in optical devices is discussed.

Concentration-Dependent Laser Performance of Yb:YAG Ceramics and Passively Q-switched Yb:YAG/Cr,Ca:YAG Lasers

“…To fully understand the nature of polarization states in passively Q-switched Yb:YAG/Cr,Ca:YAG microchip lasers, we measured the polarization states of Yb:YAG crystals and ceramics by removing Cr,Ca:YAG saturable absorber and found that Yb:YAG crystals oscillate at linearly polarization states selected by the crystalline-orientations in the (111) plane (Dong et al, 2008) and Yb:YAG ceramic oscillates at unpolarization states. Although there is saturation absorption in Cr,Ca:YAG ceramic, the same as that for Cr,Ca:YAG crystal, owing to the random distribution of Cr,Ca:YAG particles in ceramic, the saturation absorption does not exhibit crystalline-orientation dependent anisotropic properties when the sample is rotated, which is different from the anisotropic saturation absorption of Cr,Ca:YAG crystal when the laser propagate along [111] direction (Eilers et al, 1992). Therefore, the polarization states in passively Q-switched microchip lasers with Cr,Ca:YAG as saturable absorber are not only determined by the anisotropic saturation absorption of Cr,Ca:YAG saturable absorber, but also determined by the linearly polarized states of Yb:YAG crystals.…”

“…Average output power increases linearly with absorbed pump power for the four combinations, the slope efficiencies with respect to the absorbed pump power were estimated to be about 39, 36, 36 and 29% for the four combinations of C1, C2, C3 and C4, respectively. The best laser performance (low threshold and high slope efficiency) of passively Q-switched Yb:YAG/Cr,Ca:YAG microchip lasers was obtained with C1 combination because of the enhancement of linearly polarized laser operation due to the combination of linearly oscillation of Cr:YAG crystal under high intracavity laser intensity (Eilers et al, 1992) and the crystalline-orientation selected linearly polarized states of Yb:YAG crystal (Dong et al, 2008). Maximum average output power of 310 mw was obtained with Yb:YAG/Cr,Ca:YAG allcrystal combination when the absorbed pump power was 1.34 W, corresponding to opticalto-optical efficiency of 23%.…”

“…The discrepancies between all-crystals (C1) and all-ceramics (C2) combinations were caused by the optical quality of Yb:YAG crystal and Yb:YAG ceramic, the laser performance of Yb:YAG crystal is better than its ceramic counterpart. The discrepancies between C3 and C4 were attributed to the linearly polarization, with Cr,Ca:YAG crystal as saturable absorber, the extinction ratio of the polarization is stronger than that of with Cr,Ca:YAG ceramic as saturable absorber, the laser prefers to oscillate more efficiently with orientation selected anisotropic saturbable absorption of Cr,Ca:YAG crystal along <111> direction under high intracavity intensity (Eilers et al, 1992). Owing to the broad emission spectrum of the Yb:YAG materials around 1.03 μm (about 10 nm in FWHM), many longitudinal modes can be excited even for a 1-mm-thick Yb:YAG crystal.…”

“…Linearly polarized laser output was observed in these compact passively Q-switched lasers (Li et al, 1993;Yankov 1994;Kir'yanov et al, 1999;Yoshino & Kobyashi 1999;Dong et al, 2000;Bouwmans et al, 2001). The causes of the linearly polarized output in these passively Q-switched lasers were attributed to the influence of the pump polarization (Bouwmans et al, 2001), relative orientations of the switch and an intracavity polarizer (Kir'yanov et al, 1999), temperature change induced weak phase anisotropy (Yoshino & Kobyashi 1999), and the anisotropic nonlinear saturation absorption of Cr,Ca:YAG crystal under high laser intensity (Eilers et al, 1992). The anisotropic nonlinear absorption of Cr,Ca:YAG crystal induced linearly polarization in passively Q-switched lasers with Cr,Ca:YAG as saturable absorber held until appearing of transparent rare-earths doped YAG laser ceramics .…”

The characteristics of the passively Q-switched Nd:YAG laser output energy with the initial absorbing effect of Cr4+:YAG absorber

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