Fig. 1. Schematics of CCDFG generating THz wave. (a) Schematic of photon interactions, where laser fill ratio indicates intensity of laser, red arrow indicates red-shifted process of cascaded optical difference frequency, and blue arrow indicates blue-shifted process of cascade optical difference frequency; (b) evolution of wave vectors; (c) schematic of experiment, where M1 and M2 can realize total reflection to dual idler waves, M3 can realize total reflection to dual idler waves and full transmission to dual signal wave, half wave plate changes dual idler waves from o-wave to e-wave, polarizer separates orthogonally polarized signal wave from idler wave, PE is polyethylene filter plate to filter out residual cascaded optical waves, and beam filter is used to remove residual pump waves
Fig. 2. At 300 K temperature, power density of pump wave, dual signal waves, and dual idle waves generated by coupled optical parametric amplification in AFB-KTP crystal (pump wavelength =532 nm, pump power density Ip=4000 MW/cm2, power density of seed and is 1/1019 of pump power density)
Fig. 3. At 100 K temperature, CCDFG generates THz wave and cascaded optical waves, where power density of and is 1022.77 MW/cm2 and 1027.10 MW/cm2, respectively, and power density of and is 972.78 MW/cm2 and 983.85 MW/cm2, respectively. (a) Poling period versus crystal length; (b) phase mismatch distributions of each CDFG stimulated by dual signal waves; (c) phase mismatch distributions of each CDFG stimulated by dual idler waves; (d) evolution of THz wave, and generated by stimulating CCDFG with dual signal waves and dual idler waves, where Ic-s and Ic-i indicate the power density of and ; (e) distribution of cascaded optical waves at crystal lengths = 0, 3.02, 5.00, 6.79, 7.95 mm; (f) distribution of cascaded optical waves at crystal lengths = 0, 3.02, 5.00, 6.79, 7.95 mm
Fig. 4. At 100 K, evolution of THz wave and cascaded optical waves generated in CCDFG and CDFG, where Is1=1022.77 MW/cm2,Is2=1027.10 MW/cm2, Ii1=972.78 MW/cm2, Ii2 =983.85 MW/cm2. (a) Evolution of in CCDFG and CDFG, where Ic-s denotes power density of generated by stimulating CCDFG with dual signal waves and dual idler waves, Is denotes power density of generated by CDFG; (b) evolution of in CCDFG and CDFG, where Ic-i denotes power density of generated by stimulating CCDFG with dual signal waves and dual idler waves, and Ii denotes power density of generated by CDFG; (c) THz wave power density versus crystal length, where IT,c-s denotes power density of THz wave generated by CCDFG, IT,c-i denotes power density of THz wave generated by CCDFG, IT,s and IT,i denote power density of THz wave generated by stimulating CDFG with dual signal waves and dual idler waves, respectively
Fig. 5. At 300 K temperature, CCDFG generates THz wave and cascaded optical waves, where power density of and is 1022.77 MW/cm2 and 1027.10 MW/cm2, respectively, and power density of and is 972.78 MW/cm2 and 983.85 MW/cm2. (a) Variation of poled period with crystal length; (b) phase mismatch distribution of each CDFG stimulated by dual signal waves; (c) phase mismatch distribution of each CDFG stimulated by dual idler waves; (d) evolution of THz wave, and generated by stimulating CCDFG with dual signal waves and dual idler waves; (e) distribution of cascaded optical waves at crystal length = 0, 2.28, 4.98, 5.56, 5.95 mm; (f) distribution of cascaded optical waves at crystal length = 0, 2.28, 4.98, 5.56, 5.95 mm
Fig. 6. At 300 K, evolution of THz wave and cascaded optical waves in CCDFG and CDFG, where Is1=1022.77 MW/cm2,Is2=1027.10 MW/cm2,Ii1=972.78 MW/cm2,Ii2=983.85 MW/cm2. (a) Evolution of in CCDFG and CDFG, where Ic-s denotes power density of generated by stimulating CCDFG with dual signal waves and dual idler waves, and Is denotes power density of generated by CDFG; (b) evolution of in CCDFG and CDFG, where Ic-i denotes power density of generated by stimulating CCDFG with dual signal waves and dual idler waves, Ii denotes power density of generated by CDFG; (c) THz wave power density versus crystal length
Fig. 7. THz wave power density (IT,c-i) and energy conversion efficiency (η) generated by stimulating CCDFG at different pump power densities, where =532 nm, power density of seeds and is 1/1019 of pump wave power density