Measurement of dichroic mirror using automated absolute reflectance measurement system

A dichroic mirror is a specific optical element consisting of multi layered dielectric materials that have different refractive indexes, enabling to reflect the light of some specific wavelength range and transmit the light of other wavelength range. In general, a dichroic mirror has different spectral characteristics depending on polarization condition of incident light or incident angle. Therefore, for evaluation of such dichroic mirror, it is very important to know its spectral characteristics. Absolute reflectance measurement system has specific the capability to measure both transmittance and reflection spectrum by changing the conditions, such as the incident angle or the polarization condition of the incident light. In this system, the incident light is introduced to sample with an incident angle of θ, and then the reflected light from sample is lead to the integrating sphere with a detector with an angle set as θ-2θ. Accordingly, it can measure the absolute reflectance spectrum which can’t be obtained by the general relative reflectance measurement system. In addition, influence form light source fluctuation is removed using the double beam method by introducing the reference beam to inside of integrating sphere.

This time, using the absolute reflection measurement system, some dichroic mirror was measured to obtain the dependence on polarization and incident angle.