Detection of a photoacoustic signal using resonance grating

Abstract

Photoacoustic signal detection is becoming a popular field of research. It is providing accurate measurement techniques in spectroscopy, tissue engineering, clinical imaging and labelling. It provides good competition especially for modern all-optical methods in biosensing, as acoustic waves experience less disturbance in tissue than electromagnetic waves. This thesis focuses on detecting photoacoustic signals with resonant waveguide-grating structures and comparing their viability to commercial methods used today. The theory behind photoacoustic signals is discussed in detail, leading to the working principles of different widely used detection methods. The structure of a resonant waveguide grating is explained, along with the optical phenomena which enable its function in different applications, especially as a photoacoustic detection sensor. In the optical modelling portion of this work, a particular resonant waveguide-grating structure is examined. The modelling was performed using a mode solver for dielectric multilayer slab waveguides along with a Grating Diffraction Calculator software. Using known parameters of dielectric layer thickness and refractive index, we find values for effective refractive index and grating period. Knowing the optimal physical properties of the component, we continue analysing the optical resonance phenomenon induced by near infrared light of 790 nm wavelength. Applying some more theoretical knowledge, we use the obtained optical characteristics to evaluate the photoacoustic detection sensitivity of the resonant waveguide grating component and compare it to other similar methods used today. Resonant waveguide gratings have a vast number of configurations and are under constant examination and experiments, but this work gives a good outlook into why they have concrete potential to be a viable alternative for photoacoustic signal detection now and in the future.