What is a linear transmission measurement?

Linear transmission measurements measure the part of the transmitted light that passes straight through the sample. The figure at the bottom shows a schematic view of the measurement. This method does not detect the diffuse transmitted light. This measurement method is generally used on thin transparent film or glass not exceeding approximately 3 mm thickness. It is also used to confirm almost 100 % transmittance in a sample with double-sided anti-reflection coatings applied to suppress reflection.

The film holder accessory allows easy sample positioning for linear transmitted light measurements. The photo at top right shows the appearance of the film holder. During actual measurements, the film holder is installed in the standard sample compartment. Baseline correction is then performed. Baseline correction generally involves measurements on air with no sample mounted. After baseline correction is complete, mount the sample at the sample side and perform sample measurements. The top left figure shows the sample mounting position, viewed from directly above the film holder.