Realization of high depth resolution using two-beam self-mixing interferometry with a terahertz quantum cascade laser

We study a two-beam self-mixing interference in a terahertz quantum cascade laser. The behavior of the self-mixing interference is simulated theoretically, and is demonstrated by designing experiments. The information of terahertz waves reflected from targets can be read out from the amplitude and phase of the self-mixing signals. Using the terahertz two-beam self-mixing interference method, a pattern on the back surface of a GaAs sample is imaged in both amplitude and phase modes, with the terahertz laser incident on the front surface. The sample thickness variation is accurately measured with a depth resolution in micron scale. Our study provides a way for achieving high precision terahertz far-field thickness measurement and imaging.