Geometric Optical Experiments Using Water Mixed with Highlighter Ink

The laser pointer has been widely used to demonstrate some simple optics phenomena, like reflection, refraction, total reflection, and diffraction. However, the rays of laser light cannot be seen in the air because the scattered light is too weak. Many physics teachers use milk or smoke to visualize rays of laser light in physics labs, but it is hard to demonstrate some experiments, such as diffraction. Recently, Velasco and del Mazo demonstrated an interesting experiment in which four optical phenomena could be visualized by using a rhodamine B solution. However, the color change of the laser beam (532 nm) is not easy to explain for students who have just learned optics. In this study, we developed a simple way of visualizing geometric optical experiments in water mixed with highlighter ink to eliminate the influence of color change. Our material list includes a green highlighter, a large transparent rectangular tank filled with water, a smaller transparent square container, a round acrylic plate, a prism, a concave acrylic plate, a beaker, and a CD grating.