Double-layered nitrocellulose membrane sample holding technique for THz and FIR spectroscopic measurements.

Gretel M Png,Ruth Plathe,Bernd M Fischer,Dominique Appadoo,Derek Abbott

doi:10.1364/oe.23.004997

Abstract

In terahertz (THz) and far-infrared (FIR) spectroscopic measurements, weak absorption spectral features due to small quantities of test sample can be masked by undesirable etalon fringe artifacts caused by multiple reflections within a pellet or a rigid sample holder. A double-layered nitrocellulose (NC) membrane structure is proposed in this paper as an alternative holder for small quantities of either dry or wet pure (no added polyethylene powder) samples with significantly reduced etalon artifacts. Utilizing a THz time-domain spectroscopy system and a synchrotron source, we demonstrate the performance of the NC structure across the THz/FIR spectrum, benchmarking against pellets holding similarly small quantities of α-lactose powder either with or without different grades of polyethylene powder. With only pure samples to consider, scattering can be mitigated effectively in NC-derived spectra to reduce their baselines.

Highlights

To relate bare lattice results of hadron matrix elements and decay constants to phenomenological numbers, which are usually given in the MS scheme, the underlying operators need to be renormalized
We have demonstrated that the Feynman–Hellmann method is an effective approach to calculating renormalization factors
For nonsinglet operators no additional gauge field configurations have to be generated. For singlet operators it appears that only a couple of different background field strengths need to be realized in order to make an accurate and precise calculation

Summary

Introduction

To relate bare lattice results of hadron matrix elements and decay constants to phenomenological numbers, which are usually given in the MS scheme, the underlying operators need to be renormalized. In this paper we propose an alternative method, based on the Feynman–Hellmann (FH) relation, which eliminates the issue of computing disconnected contributions directly at the expense of requiring the generation of additional ensembles of gauge field configurations. This essentially involves computing two-point correlators only in the presence of generalized background fields, which we show arise from introducing the operator O into the action,.

The Feynman–Hellmann method

Numerical results and tests

Axial vector current

Scalar density

Conclusions