Fig. 1. Experimental setup. S, sampler; M1∼M3, mirrors; L1, 2, lenses; EOC, ⟨110⟩ ZnTe EO crystal; Si, silica wafer; BS1, 2, beam splitters; OAPM, off-axial parabolic mirror; SPIDER, spectral phase interferometer for direct electrical field reconstruction; P, polarizer.

Fig. 2. Geometry of THz EO detection based on ⟨110⟩ ZnTe crystal. The plane of the page is the (110) plane of the crystal, and the angles α and θ are measured inside the (110) plane.

Fig. 3. Dependences of the phases induced by THz field on azimuthal angle α with (a) improved CP-SI and (b) MZ-SI.

Fig. 4. Measured waveforms of THz fields for different α values with the α-BBO plate (a) after and (b) in front of the EOC.

Fig. 5. (a) Normalized THz waveforms measured by three methods: traditional multi-shot scan (black line), SE-EOS averaging over 100 shots (red line), and improved CP-SI (blue line); (b) the recorded THz field noises by using improved CP-SI (gray area) and the RMS statistics over 100 shots (blue line).

Fig. 6. (a) Normalized THz waveforms measured by traditional multi-shot scan (black line) and MZ-SI (blue line); (b) the recorded THz field noises by using MZ-SI (gray area) and the RMS statistics (blue line).