Building a Custom Microscope – An Advanced Lab to Study Brownian Motion*

Our goal is to create a laboratory module for students to build an optical microscope, calibrate it, and make precise measurements of Brownian motion and diffusion using multiple approaches such as mean squared displacement analysis and differential dynamic microscopy. We constructed an optical microscope based on the design by Kemp et al. (arXiv:1606.03052). Then, using a 40x objective, we study the Brownian motion of 1 micron colloidal particles.  A digital camera is used to record videos of colloidal motion, ImageJ is used to post-process the images, and matlab is used to calculate the diffusion coefficient of the particles using two independent approaches. We use both single particle tracking and image correlation techniques to analyze colloidal diffusion. To do this, we use matlab codes for particle tracking, msd analysis, and differential dynamic microscopy analysis to calculate the diffusion coefficient. Our lab module is intended to be an introduction to physics research, fortify concepts from optics and statistical physics, and give students hands-on experience in building optical systems and analyzing noisy data.