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(Color online) Schematic of the air photonic setup for non-invasive field imaging inside a tapered parallel plate waveguide. THz radiation is coupled into the TPPWG, propagates along it, and then interacts with NIR probe inducing second harmonic generation in the presence of oscillating local electric bias field. L1, L2—lenses, F—400 nm filter, HVM—high voltage modulator, and PMT—photomultiplying tube.
(Color online) (a) Normalized maximum second harmonic intensity I 2 ω as a function of interaction length Lx between fundamental and THz beams. The 800 nm beam waist at the focus point has been calculated to be 6.5 μm and the Rayleigh range is 41 μm, pulse duration 90 fs. Inset presents considered geometry. (b) Normalized response function R(f) for Lx = 20 μm, 80 μm, and 200 μm.
(Color online) (a) 2D map of THz induced second harmonic I 2 ω (t) as a function of THz wave-probe delay time for different positions of the probe beam along the waveguide. Values of I 2 ω (t) have been corrected for the bias field. (b) Measured and simulated integrated peak THz electric field across the waveguide as a function of NIR probe position z.
(Color online) Measured and simulated frequency dependent amplitude reflection coefficient Γ of the waveguide end. Waveform from point z = −0.9 mm shown in the inset.
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