Optimized Design Of The Probe Critical Angle Refractometer Optical System

Refractive index is an important physical parameter for the optical properties of ma-terial.At the same time,the refractive index of material is closely related to the physical and chemical properties of materials.When material concentration,density,temperature and other physical quantities are changed,that will affect the material refractive index.Accordingly,physical and chemical parameters of the substance can be measured indirect-ly by measuring the refractive index of the substance.Compared to the measurement of the other liquids parameters,the refractive index is easier to measure.Therefore,the phys-ical and chemical parameters of liquid are simultaneously obtained by measuring the re-fractive index of the various media.In recent years,it has becoming an important research topic in the fields of chemistry,biology,medicine,food,beverage,material preparation and environmental science.In order to meet the actual measurement needs of industrial production and scientific research,the method of measuring liquid refractive index in situ and real-time measure-ment in the production process becomes more and more significant.This paper introduces the development status and application prospect of liquid refractive index measurement in domestic and foreign,and summarizes the classical and varieties of new liquid refractive index measurement methods in recent years.Based on the analysis of formation mecha-nism of the shading effect,the analytical relationship between the circular dark pattern and the liquid refractive index is established,and an in situ measurement method is pro-posed.The method is easy to operate,and the pattern showing as soon as the illumination,automatically formed with the liquid refractive index of the circular dark pattern without debugging and testing.Considering that the method requires a large amount of liquid sample and the depth of the liquid is not easy to measure accurately,the circular dark pat-tern is not easy to be extracted when it is formed at the bottom as well,there are some lim-itations when used for practical measurement.We have further studied and designed the probe-type critical angle refractometer on the basis of above principle.The refractometer has solved the previous problems,and its structure is simple.The refractometer can also measure the refractive index of the liquid in situ,on-line with high precision.After analyzed the sensing principle of the probe-type critical angle refractometer and determined its analytical formula,this paper describes its structural design in detail.It is known from the analytical formula that the measurement error of the probe-type critical angle refractometer is mainly from the circular dark pattern diameter.We conduct studies to optimize some parameters in the refractometer measure-ment system,such as transmission and scattering layer thickness and material,laser wave-length,laser power,laser spot size on the scattering layer and the thickness and material of the glass sensor.At last we find out relevant parameters to improve sensitivity and accura-cy in the refractometer measurement system.We also research the method of extending the measuring range and improving the sensitivity of the refractometer.Compared the several transparent and translucent liquids refractive index which was measured by using the probe-type critical angle refractometer with the measurement re-sults of the Abbe refractometer.It shows that the accuracy of the probe-type critical angle refractometer is closely equal to the commercial Digital Abbe refractor's result(±2×10-4RIU).At the same time,it is very suitable in the industrial production process on-line measurement,detection field or water pollution in the relatively harsh environment be-cause of its simple structure,durable,good anti-interference and high stability characteris-tics.It also can be used as a probe-type liquid refractive remote monitoring system.