Abstract
Terahertz wave is a light source which is still on research and development, comparing to other wave length, we are not familiar with the terahertz wave (such as thermal light or coherent light), and we want to understand the properties about it, we refer to the HBT experiment to measuring the second order correlation function of Terahertz wave, and understanding whether the terahertz wave is classical or quantum light. Because the electric field of Terahertz wave from experiment setup, to getting the second order correlation function, we need to make the electric filed signal square and multiplying with each other. Because the signal is from the lock-in amplifier, so we need to cancel the constant which we do not need after the calculation from above. Finally, the experiment results is compared to the theoretical prediction