Theoretical investigation of angle measurement based on third-harmonic generation (THG) with a femtosecond laser

In this paper, we proposed the concept of angle measurement based on third-harmonic generation (THG), which can be produced in a wider range of materials than the second harmonic generation (SHG). The theoretical investigation has been done by considering the direct third harmonic generation process, and three typical nonlinear crystals, including BBO, LiIO 3, and KDP are used for the sensitivity analysis. The analysis shows the angle dependence of the THG has the sinc function form, which means the maximum intensity can occur around the phase-matching angle. Based on this, the simulation investigation was done nearing the phase-matching angle, and the calculation results indicate that the BBO crystal has the best angular measurement sensitivity because of the low dispersion and the fast peak shift in the investigated spectral range compared with the other two crystals.