Abstract
Variable crystal quality affects the laser performance of many self-frequency doubling crystals, particularly those of the yttrium aluminum borate family. In this report we characterize nonlinear frequency conversion in Yb:YAB and demonstrate a simple non-destructive technique for measuring crystal quality. By imaging the nonlinear conversion using a CCD camera we observe phase matching characteristics similar to that obtained in quasi-phase-matched crystals. These effects are attributed to stacking faults in the structure of the YAB crystal during crystal growth. We believe that such defects cause the large variability in self-doubled performance reported for Nd- or Yb-doped YAB and that our technique may be used as a nondestructive measurement of crystal quality.
Highlights
Self frequency doubling lasers are of great interest due to their simplicity, compactness and potential for true single crystal, microchip style, visible sources
All of these host materials have been demonstrated to be capable of self-frequency conversion with either neodymium or ytterbium doping only Yb:YAB has resulted in significant second harmonic (SH) powers
We have identified defects that limit nonlinear conversion applicable to any self-frequency converting system based on this material
Summary
Self frequency doubling lasers are of great interest due to their simplicity, compactness and potential for true single crystal, microchip style, visible sources. For Nd- or Yb-doped YAB refractive indices have not been measured above 700 nm This results in large variations in calculations of the phase matching acceptance bandwidths depending on the fit of the Sellmeier equations. Using the experimental approach described above we found somewhat surprisingly that within certain parts of the crystals, for either Yb:YAB, Nd:YAB or Nd:LYAB, that rather than obtain a single sinc function for the angular acceptance we obtained multiply peaked functions In this case the second harmonic intensity was much reduced. Phase matching irregularities are common in both Nd and Yb:YAB
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