Spatial polarization variation in terahertz electromagnetic wave focused by off-axis parabolic mirror

Abstract

We have investigated the spatial distribution of the polarization state of a terahertz electromagnetic wave focused by an off-axis parabolic mirror (OPM) in the focal plane. We employed polarization-resolved terahertz time-domain spectroscopy and found that a steep spatial variation in the polarization state appears slightly distant from the focus when a linearly polarized terahertz wave is focused. The spatial variation includes an abrupt change in the polarization state (states change between circular and linear polarizations) within a wavelength. The observed phenomena are confirmed by numerical calculations and are shown to be intrinsic to the reflection from the OPM.

Terahertz Polarization Imaging and Its Applications

“…To answer this question, we constructed a terahertz E-field vector imaging system using a CCD camera [62] and investigated the spatial E-field vector distribution at the focal plane. We observed an unusual E-field vector distribution and successfully explained the experimental results by a rigorous calculation as outlined below [69,70]. Figure 4 shows the experimental setup of the terahertz E-field vector imaging system [62].…”

“…After the temporal profile of the E-field vector has been obtained at each pixel of the CCD camera, we perform the Fourier transform of the temporal profile of the E-field vector data at each pixel and extract a single frequency component. Figure 5 shows the experimental results [70]. Figure 5a plots the time evolution of the Ypolarized E-field at the focus of the parabolic mirror for the frequency component 0.75 THz.…”

“…[62] with the permission of AIP Publishing.) Figure 5 shows the experimental results [70]. Figure 5a plots the time evolution of the Y-polarized E-field at the focus of the parabolic mirror for the frequency component 0.75 THz.…”

Intra-cycle depolarization of ultraintense laser pulses focused by off-axis parabolic mirrors

“…[26,27] both account for a time dependence of the focused ultrashort pulse at an envelope level. Recently, a group working in the field of terahertz radiation reported on an experiment in which the electric and magnetic fields of a THz beam focused with a 90 • OAP mirror were characterized with sub-cycle time resolution [28,29] . In particular, the authors observed a loss of the original polarization structure and the formation of what they call electromagnetic divergence and rotation at the time of the optical cycle at which the fields are supposed to vanish.…”

One-dimensional subwavelength position determination exploiting off-axis parabolic mirror

“…Previously, we reported [27][28][29] that a transient rotational electric field distribution appears around the focus when a linearly polarized parallel light is focused by an off-axis parabolic mirror (PM). The rotational distribution in this case exhibits an interesting feature, i.e., the amplitude at each point varies linearly on the subwavelength scale.…”