Friday, 25 November 2016

Terahertz frequency-wavelet domain deconvolution for stratigraphic and subsurface investigation of art painting

Junliang Dong ; J. Bianca Jackson ; Marcello Melis ; David Giovanacci ; Gillian C. Walker ; Alexandre Locquet ; John W. Bowen, and D. S. Citrin


Terahertz frequency-wavelet deconvolution is utilized specifically for the stratigraphic and subsurface investigation of art paintings with terahertz reflective imaging. In order to resolve the optically thin paint layers, a deconvolution technique is enhanced by the combination of frequency-domain filtering and stationary wavelet shrinkage, and applied to investigate a mid-20th century Italian oil painting on paperboard, After Fishing, by Ausonio Tanda. Based on the deconvolved terahertz data, the stratigraphy of the painting including the paint layers is reconstructed and subsurface features are clearly revealed, demonstrating that terahertz frequency-wavelet deconvolution can be an effective tool to characterize stratified systems with optically thin layers.

Full article here.

Double Fano resonance with externally driven subradiant mode

Y.U. Lee ; J.W. Wu


In this study, we observe that a dark mode is not necessarily prerequisite for an asymmetric Fano resonance to take place in plasmonic structures. The characteristic asymmetry feature of Fano resonance is retained in a plasmonic structure when both superradiant and subradiant oscillators are externally driven. Double Fano resonances are experimentally and theoretically observed where a common subradiant driven oscillator is coupled with two superradiant oscillators. As a classical analogue of a four-level tripod atomic system, the extinction spectrum of the composite metamaterial exhibits a coherent effect based on double Fano resonances. Transfer of the absorbed power between two orthogonal superradiant oscillators is shown to be mediated by the common subradiant oscillator.

Full article available here.

Identification of traditional Chinese medicines by using terahertz time-domain spectroscopy

Jun Zhou


Terahertz time-domain spectroscopy (THz-TDS) has been applied to the identification of traditional Chinese medicines. It was found that THz-TDS combined with chemometrics can be used to identify traditional Chinese medicines very well.

Full article available here.

Thursday, 10 November 2016

THz spatial filter integrating bimaterial switching for sensors

Varittha Sanphuang ;  Niru K. Nahar ;  John L. Volakis


We propose a THz spatial filter using frequency selective surfaces (FSS) integrated with bimaterial actuator for switching. The actuator consists of two materials that have different thermal expansion rates and can be designed based on temperature tuning. The goal for this design is to develop high performance reconfigurable filters operating in the THz band. The filter was fabricated using gold as filter pattern on silicon substrate. SiO2 and Al were used as bimaterial actuators. Simulations show excellent transmittance (>80%). Allowing different gap of the actuator (up and down), the peak frequency can vary from 0.35 to 0.37 THz.

Full article available here.

Wednesday, 31 August 2016

Pharmaceutical applications of terahertz spectroscopy and imaging

Daniel Markl ; Michael T. Ruggiero and J. Axel Zeitler

Terahertz spectroscopy and imaging techniques have advanced the chemical and physical characterisation of active pharmaceutical ingredients (APIs), excipients and final solid dosage forms. Terahertz radiation can be used to investigate both chemical and solid structures, as well as provide information on the bulk morphology of pharmaceutical materials. The penetrating and non-destructive properties of terahertz light, coupled with its high acquisition rate, makes this technology a promising candidate for process analytical technology (PAT) applications.

Terahertz radiation corresponds to frequencies between the microwave and infrared regions of the electromagnetic spectrum (300 GHz to 10 THz, or wavelengths of 1mm to 1μm). For many years the terahertz region had been referred to as the ‘terahertz gap’ because of the difficulties in generating and detecting terahertz light. This has changed over the past few decades due to major advances that have brought down costs and instrument size, from $500,000+ laser systems that can take up an entire laboratory space to sub-$100,000 benchtop – and even hand-held – devices. Such breakthroughs have brought terahertz techniques into the mainstream and have enabled terahertz technologies to be implemented in industrial settings.

The full article can be accessed here (subscription required): link