Design Considerations for Integration of Terahertz Time-Domain Spectroscopy in Microfluidic Platforms

Rasha Al-Hujazy,Christopher Collier

doi:10.3390/photonics5010005

Rasha Al-Hujazy, Christopher Collier

Open Access

https://doi.org/10.3390/photonics5010005

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Journal: Photonics	Publication Date: Mar 10, 2018
Citations: 10	License type: CC BY 4.0

Affiliation: University of Guelph

Abstract

Microfluidic platforms have received much attention in recent years. In particular, there is interest in combining spectroscopy with microfluidic platforms. This work investigates the integration of microfluidic platforms and terahertz time-domain spectroscopy (THz-TDS) systems. A semiclassical computational model is used to simulate the emission of THz radiation from a GaAs photoconductive THz emitter. This model incorporates white noise with increasing noise amplitude (corresponding to decreasing dynamic range values). White noise is selected over other noise due to its contributions in THz-TDS systems. The results from this semiclassical computational model, in combination with defined sample thicknesses, can provide the maximum measurable absorption coefficient for a microfluidic-based THz-TDS system. The maximum measurable frequencies for such systems can be extracted through the relationship between the maximum measurable absorption coefficient and the absorption coefficient for representative biofluids. The sample thickness of the microfluidic platform and the dynamic range of the THz-TDS system play a role in defining the maximum measurable frequency for microfluidic-based THz-TDS systems. The results of this work serve as a design tool for the development of such systems.

Highlights

The development of ultrafast pulsed lasers was a significant scientific achievement, with a plethora of applications including semiconductor characterization [1,2], optical interferometric studies [3,4], and material analyses [5], and was a key advancement to allow electromagnetic measurements over the terahertz (THz) spectrum [6,7,8,9]
Tang et al [25] and George et al [26] have both initiated work integrating such microfluidic-based terahertz time-domain spectroscopy (THz-TDS) systems. These microfluidic-based THz-TDS systems require careful design considerations due to significant and fundamental challenges. These challenges are caused by a twofold effect: the maximum measurable absorption coefficient of a THz-TDS system monotonically decreases from its maximum; while simultaneously, the absorption coefficient of most liquids monotonically increases over the THz spectrum [27]
Where the dynamic range function is DRF(f ) (being Eref (f ) normalized with respect to its noise floor) and n is the refractive index of water over the THz spectrum. (This fundamental equation was initially reported by Jepsen and Fischer [34] and its derivation is given in the Appendix.) A piece-wise equation for the refractive index of water is fit to data reported by Wang et al [38]