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A THz detector with both high sensitivity and fast time response has been required for industrial applications such as nondestructive testing (NDT), security, and spectroscopy. Through a collaboration with the Technical University of Denmark (DTU), we have recently developed a THz-sensitive point detector and imager based on metasurface and photomultiplier tube (PMT) and image intensifier (I.I.) technologies, respectively. A fast time response is one of the unique characteristics of these devices: the PMT-based point detector provides a nanosecond response time while the I.I.based imager is capable of frame rates up to 1000 fps. These devices have a double split-ring resonator (DSRR) at the photocathode for THz-electron conversion (metasurface). In this paper, we discuss the two devices and report on the development and results for increasing their sensitivity for ultrafast, broadband THz pulses by sharpening the field-enhancing antenna tips. This leads to a smaller tip diameter, which increases the electric field confinement and thus intensity at the tip, making the field emission more likely to occur at lower field strengths as a result. Both devices thus offer a sensitive and simple method to detect THz frequencies easily, with the I.I. offering a handheld, 9V battery-powered device.

Terahertz pulse time-domain holography (THz PTDH) is an ultimate technique both for the measurement of object optical properties and broadband wavefront sensing. However, THz PTDH has valuable restriction connected with low signal-to-noise ratio which becomes a serious issue in coherent measurements. This noise problem could be solved by filtering with use of modern block-matching algorithms based on nonlocal similarity of small patches of images existing in investigated objects. Here we present the study on the use of denoising algorithms applied for hyperspectral THz data in the spatio-temporal and spatial-spectral domain. We provide a numerical simulation of denoising in case of broadband uniform topologically charged (BUTCH) beam of pulsed THz radiation. publishedVersion

A multimode horn differs from a single mode horn in that it has a larger sized waveguide feeding it. Multimode horns can therefore be utilized as high efficiency feeds for bolometric detectors, providing increased throughput and sensitivity over single mode feeds, while also ensuring good control of the beam pattern characteristics. Although a cavity mounted bolometer can be modelled as a perfect black body radiator (using reciprocity in order to calculate beam patterns), nevertheless, this is an approximation. In this paper we present how this approach can be improved to actually include the cavity coupled bolometer, now modelled as a thin absorbing film. Generally, this is a big challenge for finite element software, in that the structures are typically electrically large. However, the radiation pattern of multimode horns can be more efficiently simulated using mode matching, typically with smooth-walled waveguide modes as the basis and computing an overall scattering matrix for the horn-waveguide-cavity system. Another issue on the optical efficiency of the detectors is the presence of any free space gaps, through which power can escape. This is best dealt with treating the system as an absorber. Appropriate reflection and transmission matrices can be determined for the cavity using the natural eigenfields of the bolometer cavity system. We discuss how the approach can be applied to proposed terahertz systems, and also present results on how the approach was applied to improve beam pattern predictions on the sky for the multi-mode HFI 857GHz channel on Planck.

The Heterodyne Instrument for the Far-Infrared (HIFI) is one of three instruments to be launched aboard the Herschel Space Observatory (HSO) in 2009. HIFI will provide unprecedented spectral sensitivity and resolution between 490-1250 GHz and 1410-1910 GHz. In this paper, we report on the analysis of electrical standing waves that are present between the hot electron bolometer (HEB) heterodyne mixing element and the first low noise amplifier in the HIFI instrument. We show that the standing wave shape is not a standard sinusoid and difficult to remove from the resulting spectrum using standard fitting methods. We present a method to remove the standing waves based on data taken during the HIFI instrument level test, and anticipate the use of a similar calibration procedure in actual flight. Using the standing wave profile we obtain direct evidence of the complex IF output impedance of the HEB mixer.