Coherence time in periodically modulated light beams

The study of the coherence properties of modulated light sources is interesting since their utilization has increased considerably. After introducing in an intuitive way the coherence time definition, we present a systematic method for calculating the coherence time of a periodically modulated intensity light beam. The results are applied to two cases: chopped light and pulsed laser light. A comment is made about the results and an experiment to prove the change of coherence properties with the modulation period is described.