Pump-probe microscopy in a Sagnac interferometer

An interferometric pump-probe microscope with two counterpropagating probe beams is developed and characterized. Application of the technique to a porphyrin derivative thin film shows that the technique is sensitive to variations in local film morphology that are undetectable with conventional pump-probe techniques. Analysis of the material response shows that the technique enhances signal levels measuring transient changes in the optical constants, limited by the asymmetry of the probe beam beamsplitter. The technique also provides the ability to distinguish contributions to the overall pump-probe response from changes to the real and imaginary components of the optical constants.