Estimation of Spectroscopic Uncertainty and Correlation in Terahertz Time Domain Spectroscopy

We present a method of calculating the measurement variance-covariance matrix of a spectroscopic sample’s complex refractive index from time-domain statistics in order to estimate uncertainty of a measurement. We compare this method to a numerical analysis and previously derived methodology, and show that our time-based estimate is both accurate and adaptable to complex extraction models

Multilayer Extraction of Complex Refractive Index in Broadband Transmission Terahertz Time-Domain Spectroscopy

In terahertz spectroscopy, multi-layered samples often need to be measured, for instance in a liquid flow cell, and this complicates the extraction of material parameters. We present a spectroscopic parameter extraction algorithm for multilayer samples that can also be used to extract the thickness of an unknown sample laye

Probing temperature- and solvent-dependent protein dynamics using terahertz time-domain spectroscopy

The effect of temperature on the terahertz-frequency-range material properties of lyophilized and single-crystal hen egg-white lysozyme has been measured using terahertz time-domain spectroscopy, with the results presented and discussed in the context of protein and solvent dynamical and glass transitions. Lyophilized hen egg-white lysozyme was measured over a temperature range from 4 to 290 K, and a change in the dynamical behaviour of the sample at around 100 K was observed through a change in the terahertz absorption spectrum. Additionally, the effect of cryoprotectants on the temperature-dependent absorption coefficient is studied, and it is demonstrated that terahertz time-domain spectroscopy is capable of resolving the true glass transition temperature of single-crystal hen egg-white lysozyme at 150 K, which is in agreement with literature values measured using differential scanning calorimetry

Accurate Parameter Extraction From Liquids Measured Using On-chip Terahertz Spectroscopy

We introduce a method for estimating the permittivity of liquid samples measured using integrated microfluidic/planar Goubau line terahertz waveguides, in which simulation results are incorporated with measurement data to enable accurate frequency-dependent analysis

A Board Level Intervention to Develop Organisation-Wide Quality Improvement Strategies: Cost-Consequences Analysis in 15 Healthcare Organisations

BACKGROUND: Hospital boards have statutory responsibility for upholding the quality of care in their organisations. International research on quality in hospitals resulted in a research-based guide to help senior hospital leaders develop and implement quality improvement (QI) strategies, the QUASER Guide. Previous research has established a link between board practices and quality of care; however, to our knowledge, no board-level intervention has been evaluated in relation to its costs and consequences. The aim of this research was to evaluate these impacts when the QUASER Guide was implemented in an organisational development intervention (iQUASER). METHODS: We conducted a 'before and after' cost-consequences analysis (CCA), as part of a mixed methods evaluation. The analysis combined qualitative data collected from 66 interviews, 60 hours of board meeting observations and documents from 15 healthcare organisations, of which 6 took part on iQUASER, and included direct and opportunity costs associated with the intervention. The consequences focused on the development of an organisation-wide QI strategy, progress on addressing 8 dimensions of QI (the QUASER challenges), how organisations compared to benchmarks, engagement with the intervention and progress in the implementation of a QI project. RESULTS: We found that participating organisations made greater progress in developing an organisation-wide QI strategy and became more similar to the high-performing benchmark than the comparators. However, progress in addressing all 8 QUASER challenges was only observed in one organisation. Stronger engagement with the intervention was associated with the implementation of a QI project. On average, iQUASER costed £23 496 per participating organisation, of which approximately 44% were staff time costs. Organisations that engaged less with the intervention had lower than average costs (£21 267 per organisation), but also failed to implement an organisation-wide QI project. CONCLUSION: We found a positive association between level of engagement with the intervention, development of an organisation-wide QI strategy and the implementation of an organisation-wide QI project. Support from the board, particularly the chair and chief executive, for participation in the intervention, is important for organisations to accrue most benefit. A board-level intervention for QI, such as iQUASER, is relatively inexpensive as a proportion of an organisation's budget

THz-TDS of liquids in a temperature-controlled transmission flowcell

Precise temperature-control is necessary for many spectroscopic measurements. We present the temperature-dependent complex THz refractive index of liquid samples measured in a flowcell, analysed by a numerical method that allows simultaneous extraction of the sample's thickness to verify the temperature-stability of the cell

The Development of a Semtex-H Simulant for Terahertz Spectroscopy

The development and use of terahertz (THz) frequency spectroscopy systems for security screening has shown an increased growth over the past 15 years. In order to test these systems in real-world situations, safe simulants of illicit materials, such as Semtex-H, are required. Ideally, simulants should mimic key features of the material of interest, such that they at least resemble or even appear indistinguishable from the materials of interest to the interrogating technique(s), whilst not having hazardous or illicit properties. An ideal simulant should have similar physical properties (malleability, density, surface energy and volatility to the material of interest); be non-toxic and easy to clean and decontaminate from surfaces; be recyclable or disposable; and be useable in a public environment. Here, we present a method for developing such an explosive simulant (for Semtex-H) based on a database of THz spectra of common organic molecules, and the use of a genetic algorithm to select a mixture of compounds automatically to form such a simulant. Whilst we focus on a security application, this work could be applied to various other contexts, where the material of interest is dangerous, impractical or costly. We propose four mixtures that could then be used to test the spectral response of any instrument, working at terahertz frequencies, without the need for an explosive substance

Free-space terahertz radiation from a LT-GaAs-on-quartz large-area photoconductive emitter

We report on large-area photoconductive terahertz (THz) emitters with a low-temperature-grown GaAs (LT-GaAs) active layer fabricated on quartz substrates using a lift-off transfer process. These devices are compared to the same LT-GaAs emitters when fabricated on the growth substrate. We find that the transferred devices show higher optical-to-THz conversion efficiencies and significantly larger breakdown fields, which we attribute to reduced parasitic current in the substrate. Through these improvements, we demonstrate a factor of ~8 increase in emitted THz field strength at the maximum operating voltage. In addition we find improved performance when these devices are used for photoconductive detection, which we explain through a combination of reduced parasitic substrate currents and reduced space-charge build-up in the device

Spectroscopy of polycrystalline materials using thinned-substrate planar Goubau line at cryogenic temperatures.

We investigate the effect of substrate thickness on the transmission bandwidth of on-chip terahertz-frequency-range planar Goubau lines both experimentally and theoretically. The bandwidth and frequency resolution are improved through substrate thinning and geometry modifications (reducing reflections arising from the THz photoconductive generators and detectors). We demonstrate that the enhanced bandwidth (2 THz) and resolution (3.75 GHz) allows this type of on-chip waveguide to be used for spectroscopic measurements of polycrystalline materials from cryogenic (4 K) to room temperature (292 K) by recording vibrational absorption spectra from overlaid samples of lactose monohydrate