Spectral Characterization

Spectral performance of thin-film optical coatings is routinely characterized using several spectrophotometers or laser line sources. Our Hitachi U-4001 has an operational range from 200 nm to 3200 nm, and is equipped with Absolute Reflectance attachments fixed at 12° and 45° angle of incidence. The integrating sphere detector of this instrument improves the accuracy of results for thick and wedged samples. Infrared wavelengths are covered with a Perkin Elmer FTIR 1600 in the 2µm to 20 µm wavelength range. Both the Hitachi VIS/NIR spectrophotometer and the Perkin Elmer 1600 FTIR provide digital data, which improves data analysis and aids in data presentation.

In addition to spectrophotometer measurements, several laser line measurements can be employed. These higher precision measurements augment the spectrophotometer measurements, serving to verify the spectrophotmeter traces as well as allowing more extensive characterization of coating performance at specific wavelengths. CW sources include the fixed lines of several gas and solid state lasers. The cw laser sources permit very precise measurements as a function of angle of incidence and polarization direction. When necessary, ratiometer measurements are performed that further increase precision. Pulsed laser sources based on the fundamental and harmonics of Nd:YAG and the fundamental and second harmonics of a visible dye laser are also available for use.

Spectral Characterization of a 1-inch Polarizing Beamsplitter Cube. Spectrophotometer trace shows general performance. More precise laser measurements reveal tilt dependence at a single wavelength.