Prism Coupler SPA-4000

Prism Coupler SPA-4000 is a measurement system to examine thin film properties such as refractive index, thickness, dn/dT (temperature dependency of index), propagation loss, or birefringence. It utilizes the prism coupling method. In the prism coupling method, unlike ellipsometry, reflection from the backside of substrate is less likely influence a measurement result. This means that special attention is not needed to measure a layer of film even on the transparent substrate. In addition, it can analyze samples with higher index than an Abbe refractometer. Also, the prism coupling method is less influenced by surface or boundary conditions as it utilizes propagating waves inside the thin film. SPA-4000 can measure the dependence of refractive index on wavelength by changing a incident laser beam. In order for the prism coupler to simultaneously obtain the refractive index and thickness of the film, it needs to detect at least two modes. To ensure this, the sample thickness generally needs to be at least as long as the laser wavelength. It’s sometimes called Sairon Prism Coupler attributed to its original manufacture’s name.