Abstract-Highly precise and accurate terahertz polarization measurements based on electro-optic sampling with polarization modulation of probe pulses

Natsuki Nemoto, Takuya Higuchi, Natsuki Kanda, Kuniaki Konishi, and Makoto Kuwata-Gonokami  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-15-17915

Optics Express, Vol. 22, Issue 15, pp. 17915-17929 (2014)
http://dx.doi.org/10.1364/OE.22.017915

We have developed an electro-optic (EO) sampling method with polarization modulation of probe pulses; this method allows us to measure the direction of a terahertz (THz) electric-field vector with a precision of 0.1 mrad in a data acquisition time of 660 ms using a 14.0-kHz repetition rate pulsed light source. Through combination with a THz time-domain spectroscopy technique, a time-dependent two-dimensional THz electric field was obtained. We used a photoelastic modulator for probe-polarization modulation and a (111)-oriented zincblende crystal as the EO crystal. Using the tilted pulse front excitation method with stable regeneratively amplified pulses, we prepared stable and intense THz pulses and performed pulse-by-pulse analog-to-digital conversion of the signals. These techniques significantly reduced statistical errors and enabled sub-mrad THz polarization measurements. We examined the performance of this method by measuring a wire-grid polarizer as a sample. The present method will open a new frontier of high-precision THz polarization sensitive measurements.

© 2014 Optical Society of America

Abstract-Generation of broadband terahertz vortex beams

Ryo Imai, Natsuki Kanda, Takuya Higuchi, Kuniaki Konishi, and Makoto Kuwata-Gonokami  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-13-3714

Optics Letters, Vol. 39, Issue 13, pp. 3714-3717 (2014)
http://dx.doi.org/10.1364/OL.39.003714

We propose and demonstrate a method for generating broadband terahertz (THz) vortex beams. We convert a THz radially polarized beam into a THz vortex beam via achromatic polarization optical elements for THz waves and characterize the topological charge of the generated vortex beam by measuring the spatial distribution of the phase of the THz wave at its focal plane. For example, a uniform topological charge of +1 is achieved over a wide frequency range. We also demonstrate that the sign of the topological charge can be easily controlled. By utilizing the orbital angular momentum of the beam, these results open new THz wave technologies for sensing, manipulation, and telecommunication.

© 2014 Optical Society of America