This section provides an overview for abbe refractometers as well as their applications and principles. Also, please take a look at the list of 10 abbe refractometer manufacturers and their company rankings.
Table of Contents
An Abbe refractometer is a device that can measure the refractive index of a material using the critical angle method.
It resembles a microscope in appearance, and measurements are made visually through the eyepiece. The refractive index of a sample, such as a liquid or solid, is determined by placing a small amount of the sample on a prism and observing the bright and dark areas created by the light emitted from the prism.
It is an indispensable device for manufacturers of optical equipment because it can evaluate optical materials such as optical film and optical glass.
The Abbe refractometer can determine the refractive index of a sample. It can accurately measure samples in a variety of states, including liquids, solids, and films. By determining the refractive index of a sample, it is possible to evaluate the optical performance of films, glass, lenses, etc., and is therefore used by manufacturers and analysis companies.
The refractometer principle is also used in hand-held sugar meters. Glycometers can measure the concentration of sucrose in a sample, allowing evaluation of the sweetness of vegetables and fruits.
The Abbe refractometer looks like a microscope and is used by placing a sample on a prism. Looking through the eyepiece, the light emitted from the prism and its brightness or darkness can be observed. Since the refractive index changes with temperature, some prisms have thermostatic water circulating around them.
When light is incident from a material with a large refractive index toward a material with a small refractive index, total reflection occurs when the angle of incidence exceeds a certain angle. The minimum angle of incidence at this point is called the critical angle. When a sample is placed on a prism with a higher refractive index than the sample and light is irradiated at the boundary between the prism and the sample, light incident parallel to the boundary surface is refracted at the critical angle.
When looking at the light emitted from the prism, a difference in light intensity occurs between the region above the critical angle and the region below it, allowing the observation of light and dark areas. By observing this boundary line, the refractive index of the sample can be determined. Specifically, the refractive index can be calculated from the critical angle, the angle of light emitted from the prism, the apex angle of the prism, and the refractive index of the prism.
Some models can measure the refractive indices of solids as well as liquids. However, when measuring solids, if the contact surface with the prism surface is uneven, accurate measurement is not possible. Therefore, unlike the case of liquids, polishing of the sample and the use of an intermediate liquid are necessary.
The analysis procedure for solid samples is as follows:
Normally, the refractive index of a sample is measured using the D line of the sodium spectrum (median wavelength 589.3 nm). However, depending on the model, the wavelength of the light source can be changed in the range of visible light or infrared light to measure the refractive index at different wavelengths. The advantage is that more information can be obtained than when analyzing the sodium spectrum alone.
There are several ways to change the wavelength of a light source, such as using an optical filter to transmit only a specific wavelength, or using an excitation element other than sodium (mercury, cadmium, etc.).
Generally, light with shorter wavelengths is refracted more and light with longer wavelengths is refracted less. Therefore, when the light source wavelength is on the horizontal axis and the refractive index is on the vertical axis, a rightward curve is drawn. Since the shape of this curve varies depending on the substance, it can be used to identify the type of substance and to check for the presence of impurities.
In addition, the refractive index can be efficiently measured at multiple wavelengths in the development and inspection of materials for which the refractive index is an important control item.
*Including some distributors, etc.
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