UV-VIS Dual-band Method for Optical Refractive Index Measurement Using Three Wavelengths

Using an X-cube prism, corner cube, and the optoelectronic (E-O) device, we developed a refractive index measurement method of the ultraviolet-visible (UV-VIS) dual-band optical material. A corner cube and a three-wavelength filter module were combined to subtract the signal when there was no reflected signal to eliminate the noise of the photodetector. The X-cube prism was used to combine UV and VIS dual-band light to make UV and VIS coaxial to improve measurement convenience and reduce the size of the measurement system. The three-wavelength filter module consisted of a three-wavelength filter, a blank plate, and a black plate and was installed on circular wheels. They filtered, transmitted, or blocked light. A calcium fluoride (CaF
2
) optical flat plate was tested at a refractive index of nd 1.434 (0.5876 nm), and the transmittance spectral response range of 0.25–7.00 μm. The sample was tested 25 times. At a wavelength of 0.365 μm, the average reflectance was 2.9%. The developed method improved the measurement accuracy and increased the optical power of the light source and the sensitivity of the sensor. The noise of the electronic circuit was reduced which improved its sensitivity and gain.