Accurate Beam Profile Characterization in THz Transmission Imaging Systems

Beam profiling in terahertz systems based on a 4f configuration is revised to show that usual practices underestimate the beam waist due to the narrow point spread function of the detection arm. A rigorous assessment of the beam propagation shows that, by changing the focal distance of one of the focusing elements (lenses or parabolic mirrors), the beam profile can be obtained more accurately. Simulations of beam propagation were performed in order to validate the technique and in order to devise a calibration method that improves the accuracy of the profiling measurement. Measurements in both 4f and new configurations were also performed to check the consistency of the simulations.