Overview of Methods Used

The above block diagram gives an overview of the process that made up a single run of the experiment. Over the course of the semester, ten experiments were completed.

Building the WGM Resonator

Making a silicon dioxide WGM resonator chip is a lengthy process that takes 24 hours to complete. It can be broken down into three major parts; the addition of the resonator to the silicon dioxide chip, the xenon difluoride overnight etching, and the carbon dioxide cleaning

A WGM resonator starts as a flat silicon chip and becomes toroidal shaped after XeF2 etching. The chip is smoothed after CO2 laser illumination, which increases the Q factor.

Measuring the Q Factor in Air

  • A fiber taper is used as the medium to transfer a 660 nm laser to the edge of the resonator.
  • Once the fiber makes contact with the rim of the resonator the resonator will begin the energy storing process and the Q factor can be measured using a computer program developed by a former graduate student. This can be seen in the video below. 

Creating the PAA Hydrogel

  • The process of creating a hydrogel solution is fairly simple and takes about 30 minutes
  • The chemicals used are Poly(ethylene glycol) diacrylate (PEG), Acrylic Acid (AA), and 2,2-Dimethoxy-2-phenylacetophenone
    • PEG is a chemical with a low viscosity that acts as the base for our hydrogel
    • AA is the pH-sensitive chemical that showcases the novelty of the experiment
    • 2,2-Dimethoxy-2-phenylacetophenone, otherwise known as photoinitiator, is a powdery substance that allows for the hydrogel solution to cure under the UV light
  • The ratio is 95:5 PEG:AA with the addition of 10% of the molecular weight of the ratio in photoinitiator and then the solution is diluted to 90:10 water:hydrogel

An example of a PAA hydrogel solution is depicted above. The recipe for the PAA hydrogel was created in Fall 2017, hence the date on the label. The solution is very clear, which allows for the maximum light energy to be absorbed by the resonator

Measuring the Q Factor of the Resonator in the Hydrogel

This model was created using Autodesk Fusion 360. It is a simplified version of the glass slide seen used in the experiment to hold the resonator and hydrogel.