Lase-induced grating measurements of energy migration in Tm,Ho:YAG

We report what is to our knowledge the first direct measurement of spatial energy migration among the Tm(3+) ions in a Tm,Ho:YAG crystal at room temperature. Four-wave mixing techniques were used to establish and probe transient laser-induced population gratings in the Tm(3+) ions. The grating decay rate was measured as a function of the grating spacing. The results show the presence of spatial energy migration among the Tm(3+) ions, and the diffusion coefficient of this process was measured to be 4 x 10(-7) cm(2) s(-1) for a sample containing 8.3 x 10(20) cm(-3) Tm(3+) ions.