Fig. 1. Sketch of the TPA experimental setup.

Fig. 2. Measurement results for THz radiation (a) wavelength and (b) bandwidth.

Fig. 3. THz beam profile measurement results of the LN TPA. (a)–(d) THz beam profiles measured at 2.0, 5.0, 8.0, and 11.0 mm downstream of the THz radiation exit surface (S2) of the LN crystal. (e) The beam radii for the THz beam plotted as a function of the measurement distance. The solid curves were calculated according to the estimated M2 parameters.

Fig. 4. (a) Measured THz pulse energy as a function of frequency for different effective parametric amplification lengths L. (b) Measured pulse energy of THz wave output as a function of L at four different THz frequencies.

Fig. 5. THz parametric gain (gTHz) versus frequency. The curves represent theoretical results calculated using Eq. (2), for which three different κ values were used.