We describe a method for determining the radiative decay properties of a molecule by studying the saturation of laser-induced fluorescence and the associated power broadening of spectral lines. The fluorescence saturates because the molecules decay to states that are not resonant with the laser. The amplitudes and widths of two hyperfine components of a spectral line are measured over a range of laser intensities and the results compared to a model of the laser-molecule interaction. Using this method we measure the lifetime of the A(v=0) state of CaF to be tau=19.2 pm 0.7 ns, and the Franck-Condon factor for the transition to the X(v=0) state to be Z=0.987 (+0.013 || -0.019). In addition, our analysis provides a measure of the hyperfine interval in the lowest-lying state of A(v=0), Delta_e=4.8 pm 1.1 MHz.
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