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THz microscopic imaging is used to extract the Gouy phase shift of the transverse and longitudinal field components of a tightly focused, radially polarized beam. We demonstrate that the applied THz time domain approach allows to observe directly the evolution of the geometric phase as the wave propagates through the focus. Our method yields a Gouy phase shift of 2π for the transverse component and...
Compressive THz imaging holds the potential for increased spatial resolution and imaging speed when only a small number of detectors is available. The understanding of illumination patterns is essential in determining the performance for a compressive imaging setup. The results presented here start with an evaluation of the performance of different mask types. Then the influence of deviations of the...
We combine sub-cycle, mid-infrared spectroscopy and near-field microscopy to achieve a spatial resolution of 25 nm and a temporal resolution of 50 fs. Using our nano-FTIR technology we can spatially, temporally and spectrally resolve the femtosecond carrier-dynamics in solid state materials like photo excited InAs nanowires.
We present contact-free THz near-field measurements at large-area graphene covered by an ion gel top-gate. In dependence of the gate-voltage, we map the THz near-field transmission amplitude and the resulting sheet resistance distribution across the graphene layer. High-resolution access to the local charge carrier properties of the buried graphene enables the visualization of inhomogeneity and defects...
Capturing the microscopic motion of an individual molecule on the femtosecond time scale with atomic spatial resolution has remained a key open challenge of modern nanoscience. Here, we bring the concept of lightwave-driven sub-cycle charge transport, the paradigm underlying high-harmonic generation, to a new arena of atomic spatial resolution. We enter an unprecedented regime of ultrafast lightwave-driven...
Low frequency THz radiation is visualized by means of a charged-coupled device designed for optical frequencies and a CMOS sensor. This technological advance opens novel opportunities in THz imaging as it offers smallest pixel size and large chip size at low cost. Furthermore the sensor is insensitivity to background noise and is able to detect radiation of multiple spectral ranges from x-rays to...
We applied a recently developed, ultrafast terahertz measurement technique to screen folded cardboard boxes for package inserts. The presence or absence of an enclosed leaflet can be detected unambiguously at sample speeds up to 21 m/s, and for samples with an area overlap up to 60%. The simple, robust measurement setup may pave the way to new applications of terahertz technology for quality control...
A 60 GHz high spatial resolution millimeter near-field scanning microwave microscope (NFSMM) system is developed with aim of non-destructive testing of material and circuits. Like SNOM, it involves a modulation of the probe-to-sample distance. We derive an analytical model of the probe detection versus the standoff distance and the harmonic order used for lock-in detection. Both the model and experiments...
We demonstrate terahertz (THz) apertureless near-field microscopy exploiting the self-mixing effect in a quantum cascade laser (QCL). A THz wave is scattered by a sharp needle positioned above an object and coupled back into the QCL cavity resulting in detection of the THz near-field signal through the self-mixing effect. Using this technique we demonstrate two-dimensional imaging at 2.53 THz with...
We have proposed a novel design for a contact grating setup with an incorporated Fabry-Perot resonator for intense terahertz (THz) light generation. This setup is scalable and extremely compact as compared with the conventional LiNbO3 prism setup. We evaluated the THz generation process in the device by experimental and calculated studies, and optimized the device to obtain maximum THz output.
We present transmission properties of sub-wavelength apertures (<λ/100) and discuss their applications in the collection-mode near-field probe for use with terahertz time domain spectroscopy (THz-TDS). In the deep sub-wavelength regime, the aperture transmission contains mostly evanescent field components. We have characterized the transmission properties experimentally in the THz range for 2,...
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