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Scherger B.,University of Marburg | Scheller M.,University of Marburg | Jansen C.,University of Marburg | Koch M.,University of Marburg | And 2 more authors.
Applied Optics | Year: 2011

We present a simple and versatile approach for fabricating terahertz lenses based on compression molding of micropowder polymer materials in a tabletop hydraulic press. To demonstrate the feasibility of this approach, a biconvex lens shape is calculated using a ray-tracing algorithm and lenses based on two different micropowders are fabricated. As the powder materials have different refractive indices, the resulting lenses share the same geometric shape but differ in their respective focal length. The focusing properties of the lenses are evaluated by transversal and sagittal beam profile measurements in a fibercoupled terahertz time-domain spectroscopy system, confirming the excellent imaging qualities of the compression molded lenses. © 2011 Optical Society of America.

Scherger B.,University of Marburg | Born N.,University of Marburg | Jansen C.,University of Marburg | Schumann S.,University of Marburg | And 3 more authors.
IEEE Transactions on Terahertz Science and Technology | Year: 2012

We present a terahertz transmission blaze-grating, which can be fabricated, easily, cost efficiently and in large numbers using compression molding of micro-powder. The diffraction properties of the grating are derived by simulation of electro-magnetic field scattering and are compared with angle-dependent measurements obtained in a terahertz time-domain setup. An excellent match between simulation and measurement is found, demonstrating the ability of the terahertz transmission blaze-grating for spatial dispersion of terahertz waves. Thus, this and similar terahertz transmission blaze-gratings can be used as dispersive elements for applications such as spectrometers or novel THz imaging systems. © 2011-2012 IEEE.

Every A.G.,University of Witwatersrand | Utegulov Z.N.,Nazarbayev University | Veres I.A.,Research Center for Non Destructive Testing GmbH
Journal of Applied Physics | Year: 2013

An approach is presented for calculating thermoelastic generation of ultrasound in a metal plate exposed to nanosecond pulsed laser heating, sufficient to cause melting but not ablation. Detailed consideration is given to the spatial and temporal profiles of the laser pulse, penetration of the laser beam into the sample, the appearance and subsequent growth and then contraction of the melt pool, and the time dependent thermal conduction in the melt and surrounding solid throughout. The excitation of the ultrasound takes place during and shortly after the laser pulse and occurs predominantly within the thermal diffusion length of a micron or so beneath the surface. It is shown how, because of this, the output of the thermal simulations can be expressed as axially symmetric transient radial and normal surface force distributions. The epicentral displacement response to these force distributions is obtained by two methods, the one based on the elastodynamic Green's functions for plate geometry determined by the Cagniard generalized ray method and the other using a finite element numerical method. The two approaches are in very close agreement. Numerical simulations are reported on the epicentral displacement response of a 3.12 mm thick tungsten plate irradiated with a 4 ns pulsed laser beam with Gaussian spatial profile, at intensities below and above the melt threshold. © 2013 AIP Publishing LLC.

Wiesauer K.,Research Center for Non Destructive Testing GmbH | Jordens C.,TU Braunschweig
Journal of Infrared, Millimeter, and Terahertz Waves | Year: 2013

In the last few years, various studies on terahertz (THz) birefringence have been presented, based on polarization-sensitive THz time-domain spectroscopy. The field of THz birefringence is a wide one covering several aspects, such as different materials exhibiting THz birefringence, polarization-sensitive THz technology, as well as numerous methods for extracting the birefringence properties of a sample from the THz data. Therefore, this paper aims at reviewing recent results on THz birefringence measurements presented in literature, addressing the above aspects and giving an overview of the topic. Moreover, it will focus on the investigation of birefringent fibrous samples, where specific results will be discussed in detail. Altogether, this paper should give a comprehensive view on the recent achievements in the measurements of THz birefringence. © 2013 The Author(s).

Gasiorowski J.,Johannes Kepler University | Hingerl K.,Johannes Kepler University | Menon R.,Indian Institute of Science | Plach T.,Johannes Kepler University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2013

Ellipsometric measurements in a wide spectral range (from 0.05 to 6.5 eV) have been carried out on the organic semiconducting polymer, poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene] (MDMO-PPV), in both undoped and doped states. The real and imaginary parts of the dielectric function and the refractive index are determined accurately, provided that the layer thickness is measured independently. After doping, the optical properties show the presence of new peaks, which could be well-resolved by spectroscopic ellipsometry. Also for the doped material, the complex refractive index, with respect to the dielectric function, has been determined. The broadening of the optical transitions is due to the delocalization of polarons at higher doping level. The detailed information about the dielectric function as well as refractive index function obtained by spectroscopic ellipsometry allows not only qualitative but also quantitative description of the optical properties of the undoped/doped polymer. For the direct characterization of the optical properties of MDMO-PPV, ellipsometry turns out to be advantageous compared to conventional reflection and transmission measurements. © 2013 American Chemical Society.

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