Fig. 1. Terahertz diffraction diagnostic system and the matched intense terahertz source. (a) Schematic diagram of the experimental setup for the terahertz diffraction method. (b) Typical terahertz temporal waveform and (c) its corresponding spectrum. (d) Focused terahertz beam profile recorded by a terahertz camera without the double slit when L=177.8mm.

Fig. 2. Experimental and simulation results illustrating the relevance between terahertz diffraction patterns received by the terahertz camera and double-slit position. (a)–(c) Meridional diffraction fields and the corresponding diffraction patterns for different double-slit positions δ_d=−5, 0, and 8 mm, respectively. (d) Peak intensity position δ_p in terahertz diffraction patterns as a function of double-slit position δ_d.

Fig. 3. Diffraction diagnostics for monitoring the moving of the terahertz beam. (a) Experimental setup to diagnose tiny variations of the terahertz beam direction and position. (b) The pump shrinks and tilted terahertz wave is emitted when closing the iris. The green circle indicates the outline of the terahertz beam waist on the terahertz emitting surface of the LN crystal. The green Gaussian curve marked by the dashed-line arrow implies the intensity distribution of the terahertz beam when the iris is fully open. (c) Superior limit of the calculated terahertz beam profile on its emitting surface for different iris sizes. Dark purple line corresponds to Ø=40mm, blue 20 mm, and yellow 15 mm, respectively. (d) Experimental diffraction patterns received by the terahertz camera. (e) Extracted experimental movement of the terahertz beam compared with the theoretical calculations.