Beam-size effects in electro-optic sampling of terahertz pulses

Area of Science:

• Optics
• Terahertz Spectroscopy
• Nonlinear Optics

Background:

• Electro-optic sampling is a key technique for terahertz (THz) pulse characterization.
• The use of finite-diameter probe beams in electro-optic sampling can introduce optical artifacts.
• Understanding these artifacts is crucial for accurate THz measurements.

Purpose of the Study:

• To investigate the impact of probe pulse lensing on electro-optic sampling of THz pulses.
• To quantify the additional phase shift (Deltaeta) induced by diffraction effects.
• To assess the contribution of this phase shift to the overall measured amplitude.

Main Methods:

• Theoretical analysis of probe pulse propagation through the electro-optic crystal.
• Modeling the lensing effect due to finite beam diameter.
• Comparison of phase shifts from lensing versus direct electro-optic interaction.

Main Results:

• Finite diameter probe pulses experience a lensing effect within the electro-optic crystal.
• This lensing induces an additional far-field phase shift (Deltaeta) due to altered diffraction.
• Deltaeta is comparable in magnitude to the direct electro-optic phase shift.

Conclusions:

• The lensing effect in electro-optic sampling of THz pulses is a significant factor.
• The additional phase shift from diffraction must be considered for accurate amplitude determination.
• This finding has implications for the precision of THz time-domain spectroscopy.