Fig. 1. Schematic depiction of the analyzed setups: (a) conventional TPFP (using optical grating) or TPFP setup with reflective echelon grating, (b) hybrid-contact-grating (with optical grating on NM) and NLES-I and echelon grating on NM, (c) NLES-woI setup, and (d) RNLS setup. See text for details.

Fig. 2. Dependence of the efficiency on the crystal length using conventional, NLES-I, NLES-woI, and RNLS setups in case of two different pump pulse sources. In the case of an ultrashort pulse source, the RNLES setup was also investigated. The phase matching frequency was 0.5 THz.

Fig. 3. (a)–(c) Ratio of the side peak to the main peak of the THz pulse and (d)–(f) the efficiency of the THz generation as a function of the pump pulse duration and the crystal thickness, for (a), (d) NLES-I, (b), (e) NLES-woI, and (c), (f) RNLS cases.

Fig. 4. Shapes and spectra (insets) of the generated THz pulses by NLES-I (red), NLES-woI (blue), and RNLS (green) setups for crystal lengths of (a) 2 mm and (b) 4 mm. The pump pulse duration was appropriately chosen in order to satisfy the E_side/E_max = 10% ratio. The corresponding pump pulse durations were (a)/(b) 465 fs/475 fs, 340 fs/390 fs, and 605 fs/700 fs in the cases of NLES–I, NLES–woI, and RNLS, respectively.

Table 1. Comparison of the Different THz Generation Setups^a