Research

My research lies at the intersection between optics and engineering. I like to use light to solve interesting problems. Students interested in working on any of these research projects should email me at mbaylor at carleton dot edu.

Research Area 1: Integrated Optofluidic Devices

Images of functioning devices. [a] A waveguide only device with a laser source incident on the right. The light on the left side of the waveguide travels to a 10X microscope used to magnify the output. The output face of the waveguide is reimaged and shown in [b]. [c, d] Refractometer devices containing a fluid channel (vertical) and a waveguide (horizontal). In [c] the channel contains air. In [d] the channel contains water. Notice the difference in the amount of light scatter between the two devices in [c] and [d].

I’ve had fun combining my training in optical signal processing and elecrical engineering, and interest in chemistry to move into the field of integrated optofluidic devices. I use light-sensitive plastics, called photopolymers, to simplify the fabrication of integrated optofluidic devices. Below is a device that I built. To read more about this device, read my article: Monolithic Integration of Optical Waveguide and Fluidic Channel Structures in a Thiol-ene/Methacrylate Photopolymer.

Current research students are building apparatus to measure various important characteristics of the photopolymers used for integrated optofluidic devices. These characteristics include: refractive index of the bulk resin, optical loss per unit length, maximum change in index of refraction, stiffness, etc. As we look at various resin formulations, we want to see how these properties change. Our goal is to provide a table of materials with properties for engineers so that they can choose the appropriate resin formulation for their application. For example, one application might require a rubbery material for wearable applications, while another might require a glassy material for working in harsh environments.

Research area 2: Measuring the Gel Point of Photopolymers Using NMR

This project is a collaboration between myself and Gretchen Hofmeister in Chemistry. In order to fabricate integrated optofluidic devices with my polymer, I need to know the optical exposure necessary to reach the gel point of the polymer. The gel point is defined as the point when a material has made the transition from being a solid to being a liquid. The common way of determining the gel point is using an rheometer. Although there is a rheometer at the University of Minnesota, it’s distance from Carleton and fee structure makes it challenging to use on a regular basis. Therefore we seek a technique to measure this crucial parameter locally at Carleton using our NMR instrument.

Research area 3: Fabrication of Macroscopic Polymer Lenses

An illustration of the lens profiling process: (a) A lens before imaging; (b) the shadow projection captured by the camera. The pedestal shown was used to calibrate the image, (c) the trace of the lens profile compared with the image. This profile is used to extract information about the shape and focal length of the lens.

This research project was inspired by one of my research students, Charlotte Z. She was helping another student try to make a thin film with my polymer by suggesting that the student place a small amount of liquid resin on the surface of water. Hoping the drop of resin would spread uniformly over the surface of the water, they cured the resin with UV light. Instead, the resin formed a lens! The polymer formulation I use is hydrophobic. Due to the surface tension between the resin and water combined with the influence of gravity, the resin forms a curved surface that is hardened under UV-exposure. During her remaining three years at Carleton, Charlotte explored how different water-based substrates affect the shape of the lens. Her work, which she wrote up herself with supervision from me, is described in Effects of Varying Interfacial Surface Tension on Macroscopic Polymer Lenses.

Currently, two students read about Charlotte’s work and wanted to extend it. They are looking at how the hydrophobicity of the resin affects the shape of the lens. Our goal is to be able to control the shape of the lens on demand.

Why is this work useful? Polymer lenses are cheaper to make than glass lenses. However there usefulness is limited in precision optical applications because polymer lenses cannot be polished. Thus their surface quality is not good enough for applications that require a very smooth surface to reduce scattering. The surface quality of polymer lenses is limited because they are typically made using molds – the lens can only be as smooth as the mold. By fabricating our polymer lenses on water or water-based substrates, our lenses are limited by the surface roughness of water. If we can control the shape of the lens, then polymer could be a viable option for precision optical applications, reducing their cost and increasing the usability.