Kilohertz-resolution pump–probe spectroscopy in Pr^3+:YAlO_3

We observed saturated absorption spectra of hole widths as narrow as 10.5 kHz with an excellent signal-to-noise ratio in a cryogenic Pr(3+):YA1O(3) sample, using a frequency-stabilized dye laser in a noncollinear frequency-domain pump-probe measurement. More-detailed theoretical and experimental analyses revealed the existence of an ultranarrow peak of width 10 Hz at the center of the line shape that could be attributed to grating diffraction of the pump beam.