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We have used a magneto-optical pump-probe technique to stimulate and characterize small amplitude precession of the magnetization in a variety of thin film magnetic structures. The sample is stimulated by an optically triggered magnetic field pulse and its response probed by means of a stroboscopic measurement of the magneto-optical Kerr effect. We demonstrate that the experimental technique is sensitive to small amplitude deflections of the magnetization and present formulae that describe the frequency of precession in continuous films containing either one or two magnetic layers. We show how the dependence of the precession frequency upon the orientation and magnitude of the static field may be used to characterize a 100 Å Co thin film, a Ni 81 Fe 19 (50 Å)/Cu (20 Å)/Co (50 Å)/IrMn (100 Å) spin-valve structure, and a square Ni 81 Fe 19 element of 10 µm side and 150 nm thickness. Information may be …