If you pass a polarized white light source through a layer of limonene, the polarized plane rotates. The angle of rotation depends on the wavelength of the light, so if you pass the light that has already passed through the limonene through another polarizing plate, only light of a certain wavelength will make it through. The angle of rotation is of course proportionate to the thickness of the layer of limonene, so as the thickness of the layer of limonene changes, the color of the light that passes through will also change.
C10H16. Limonene is a substance found in citrus fruits, and has properties of optical rotation, i.e. it rotates the polarized plane of linear polarized light. There are two optically differing types of limonene, d and l. d-limonene rotates to the right, and l-limonene rotates light to the left. Limonene has a specific gravity of 0.84 g/cm3. It is used for fragrances, and recently is also being used in washing liquids.
The optical rotation characteristics of limonene can be found using a spectrophotometer and two polarizing plates, and recording the results. The measurement process is as follows.
- You fix two polarizing filters used with cameras to opposing sides of a square beaker (approximately 8cm square), and set the polarizing lens to a certain angle.
- You then pass the sample light through the beaker, and read that light into the spectrophotometer's sample chamber, and obtain the wavelength that gives the lowest transmissiveness.
You then gradually adjust the angle of the polarizing filter, and make a graph of the angle of rotation and wavelength, such as the diagram shown here. In this graph, measurements have been converted to the angle of rotation for every 10cm of fluid depth. The angle of rotation when bromide methylene is added becomes smaller proportional to the ratio of bromide methylene to limonene.
When passed through a 10cm thick layer of limonene, the difference between the angle of rotation of light with a wavelength of 400µ and light of 800µ is over 180 degrees. In this case, both wavelengths of light pass through both polarizing filters, so a definite color does not appear. To fix this, if you use a shortcut filter or a band pass filter, and reduce the difference in angle to about 90 degrees, a definite color will appear.