Laser haemocytometer

Gillgrass, Sara-Jayne 2018. Laser haemocytometer. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis describes the work carried out to provide a proof of principle coupled-cavity laser measurement for blood cell analysis, using an integrated device with capillary fill microfluidics. The development of both light source and microfluidics on the same sensing platform provides complete integration and removes the dependence on external systems. In principle, InAsP quantum dot lasers, cover a wavelength range extending into the near infrared, where the response of biological matter can provide useful diagnostic information. The suitability and limitations, of both an InAsP quantum dot and GaInP quantum well active medium, are con-sidered for the coupled-cavity structure. A InAsP quantum dot structure with an 8 nm AlGaInP barrier between each dot layer was seen to have a slight improvement in device performance, but optical gain measurements indicated that this structure would not provide sufficient gain to over-come the high losses expected in the integrated device. Consequently, a GaInP quantum well was considered a sensible choice for a proof of principle coupled-cavity measurement. The efficiency of an etched facet is key to overall performance in the coupled-cavity device and has been quantified using the gain characteristics of the quantum well structure. A value of facet efficiency was found to be ηf = 0.37 ± 0.04, which is valid for all angles of etched facet. A very low facet reflectivity of 4.9x10−9 was measured for a laser with a 14.1o etched facet. Perturbation of the optical coupling between two laser/detector sections causes a change in the measured photo-voltage signal from the device. This effect has been employed to demonstrate detection of both 10 and 6 µm microbeads. In a coupled-cavity regime, a 22.6o angled facet coupled-cavity laser pair has been shown to have a lower threshold current density than either of its individual sections, indicating its potential for sensing applications.

Item Type:	Thesis (PhD)
Date Type:	Submission
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	coupled-cavity lasers, monolithic integration, microfluidics, SU-8 microfluidics, semiconductor lasers, etched laser facets, facet efficiency, cell sensing, biosensing, haemocytometer, III-V haemocytometer, chip based sensing, segmented-contact devices, gain characterisation, quantum dots, quantum wells, InAsP QDs.
Funders:	EPSRC
Date of First Compliant Deposit:	20 May 2019
Last Modified:	03 Sep 2021 15:09
URI:	https://orca.cardiff.ac.uk/id/eprint/122616

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