Two beam self mixing interference in terahertz quantum cascade lasers

The THz quantum cascade laser (THz-QCL) based two-beam self mixing (SM) interference is achieved by re-injecting optical feedbacks from two independent targets into the laser cavity. The two-beam SM effect manifests itself in the variation of laser terminal voltage. Information of the relative position change of the two targets can be obtained by analyzing the amplitude and phase of the SM signal. Using this method, micron-scale thickness variation of a GaAs sample, about one percent of the laser wavelength, is accurately measured. Our study provides an available way to develop new terahertz nondestructive testing technology.