Transient first-order interference of two independent thermal light beams

By analyzing the transient first-order interference of two independent thermal light beams in both classical and quantum theories, we conclude that for a certain kind of thermal light, it is impossible to observe the transient first-order interference pattern by superposing two independent thermal light beams even if the degeneracy parameter of thermal light is much greater than one. The result suggests that the well-accepted classical model of a thermal light field within the coherence time is not valid for all kinds of thermal light, which is important and helpful to understand the first-order interference of thermal light.