Polarization-changeable THz time-domain spectroscopy system with a small incident-angle beam-splitter

When the polarization of terahertz (THz) light is measured with THz time-domain spectroscopy (TDS) by switching the polarization angle of THz light, it is preferable that intensities of pump and probe lights are almost constant. Pump and probe lights, which are produced through dividing a femto second (fs) laser pulses by a beam-splitter, must be correlated with orientations of THz emitter and detector as well as the THz polarization angle especially in a TDS adopting nonlinear crystal like ZnTe as an emitter and/or a detector. To achieve small change in the signal against change of the THz polarization, a THz-TDS system with a small incident-angle beam-splitter has been developed, which have smaller polarization dependency in pump and probe lights than ordinary THz-TDS systems adopting a 45-degree incident-angle beam-splitter. The change in THz signal observed with a 10-degree incident-angle THz-TDS was sufficiently small in both transmission and reflection measurements when polarization angle of THz light is switched by 90 degrees.