Using the picosecond pump-probe spectroscopy technique we measured the photomodulation temporal (with 5 ps resolution) and spectral response from 610 to 750 nm, in a thin film of poly (2,5 thienylene-vinylene) (PTV). We found a fast electronic response which decays within 4 ps, and two non-electronic responses, which are due to the photoproduced strain in the film. One response is due to the static strain, and the other is from the strain waves launched in the film following the fast exciton recombination.