Strongly birefringent cut-wire pair structure as negative index wave plates at THz frequencies

We report a new approach for the design and fabrication of thin wave plates with high transmission in the terahertz (THz) regime. The wave plates are based on strongly birefringent cut-wire pair metamaterials that exhibit refractive indices of opposite signs for two orthogonal polarization components of an incident wave. As specific examples, we fabricated and investigated a quarter- and a half-wave plate that revealed a peak intensity transmittance of 74% and 58% at 1.34 THz and 1.3 THz, respectively. Furthermore, the half wave plate displayed a maximum figure of merit (FOM) of 23 at 1.3 THz where the refractive index was -1.7. This corresponds to one of the highest FOMs reported at THz frequencies so far. The presented results evidence that negative index materials enter an application stage in terms of optical components for the THz technology.Comment: 4 pages, 3 figures, submitted to Appl. Phys. Let

Adiabatic compression of terahertz waves using metal flares

We report on the adiabatic free-space coupling of broadband terahertz (THz) radiation through a subwavelength gap using metal flares. Amplitude coupling ratios better than 30% are obtained by optimizing the curvature. This scheme shows a large potential for increasing the sensitivity in THz spectroscopy using high spatial confinement without the need of transmission optics or high precision components. The intrinsic curvature of metal sheets is already sufficient to carry out experiments downsizing the microwave approach.Peer reviewedElectrical and Computer Engineerin

Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor

We report on the layer thickness determination on dielectrically coated metal cylinders using terahertz (THz) time-domain spectroscopy. A considerable sensitivity increase of up to a factor of 150 is obtained for layers down to 2.5 um thickness by introducing an experimental geometry based on a two-cylinder waveguide sensor. The layer attached on one metal cylinder is guided in contact with the second metal cylinder in the THz beam waist. This approach uses concepts of adiabatic THz wave compression and the advantages of THz waveguides. The results are compared to measurements on free-standing layers.Peer reviewedElectrical and Computer Engineerin

Terahertz two-cylinder waveguide coupler for transverse-magnetic and transverse-electric mode operation

We report the coupling and guiding of broadband terahertz radiation using a two-cylinder waveguide coupler. For the transverse electromagnetic TEM (TM0) geometry, the two opposing metal cylinders exhibit an amplitude transmission comparable to that of the cylindrical silicon lens coupled parallel-plate waveguide, but in the transverse-electric orientation the two-cylinder coupler shows much better amplitude transmission.Peer reviewedElectrical and Computer Engineerin

Comparison of terahertz technologies for detection and identification of explosives

We present results on the comparison of different THz technologies for the detection and identification of a variety of explosives from our laboratory tests that were carried out in the framework of NATO SET-193 THz technology for stand-off detection of explosives: from laboratory spectroscopy to detection in the field under the same controlled conditions. Several laser-pumped pulsed broadband THz time-domain spectroscopy (TDS) systems as well as one electronic frequency-modulated continuous wave (FMCW) device recorded THz spectra in transmission and/or reflection. © 2014 SPIE

DOPPLER-FREE TWO-PHOTON LASER SPECTROSCOPY OF RYDBERG STATES IN ALKALINE-EARTH ELEMENTS WITH THERMIONIC DETECTION

La spectroscopie à deux-photons sans effet Doppler a été utilisée pour étudier les énergies des niveaux, les déplacements isotopiques et les structures hyperfines des séries de Rydberg msns et msnd des éléments alcalino-terreux Mg (m=3), Ca (m=4), Sr (m=5) et Ba (m=6) entre les nombres quantiques principaux n=3 et 150. Le mélange singulet-triplet dû aux interactions de configurations et les effets hyperfins induits ont été détectés. L'utilisation d'un anneau de diodes thermo-ionique a permis de réaliser des mesures à haute résolution jusqu'aux nombres quantiques principaux n ~ 160.Doppler-free two-photon spectroscopy was applied to investigate level energies, isotope shifts and hyperfine structures of msns and msnd Rydberg series of alkaline earth elements Mg (m=3), Ca (m=4 ), Sr (m=5) and Ba (m=6) between principal quantum numbers n=3 and 150. As a result configuration interactions, singlet-triplet mixing and hyperfine-induced effects were detected. The use of a thermionic ring diode allowed for high resolution measurements up to principal quantum numbers n ~ 160