The Shape of Light: Exploring Lensless Holographic Microscopy and the Tyndall Effect

"The Tyndall effect occurs when the light has a shape", when a beam of light through the colloid, from the perpendicular direction of the incident light can be observed in the colloid present a bright "pathway", this is the magical and romantic Tyndall This is the magical and romantic Tyndall phenomenon. This phenomenon is due to the wavelength of light is greater than the particle scale scattering phenomenon, and the wavelength of light closer to the particle scale scattering phenomenon is more obvious, due to the size of the scale of the particles will lead to the intensity of the scattered light, the smaller the scale, the smaller the intensity of the scattered light, and thus the phenomenon of the Tyndall effect is not obvious. The Tyndall effect is often used in the field of chemistry to distinguish between solutions and colloids: to identify solutes, the microscopic point of view of the essence of the difference is the size of the diameter of the particles of the dispersant. Therefore, it is extremely important to investigate the specific influence of particle size on the Tyndall effect. In this paper, the effect of particle size on the Tyndall effect was first investigated for milk with different fat contents (skimmed milk, low-fat milk and whole milk). In the pre-experimental stage, a simple apparatus was used to observe the difference between the three Tyndall effects with the naked eye. In order to further investigate the effect of particle size on the Tyndall effect, a high-precision microscope system is indispensable. Considering the complexity and cost of the system, we finally investigated and adopted an optical system based on digital holographic microscopy. In the experimental stage, a simple lensless microscope was designed and 3d printed independently to observe and investigate the microscopic mechanism of the Tyndall effect by observing and reconstructing the milk in three dimensions using digital holographic microscopy.