Prism coupler （Refractive index of thim films, film thickness measurente, with temperature and humidity variation） Able to measure fine thermal optical coefficients of polymer films on surfaces METRICON PC - 2000 wavelength： Measurement mode： Attachments: Applicable film thickness ： 633nm, 850nm, 1320nm, 1550nm Prism coupling mode Critical angle measurement mode （TE＆TM） Fine-tunable heater (home-made) measurement of thermal optical coefficients > 3 micrometer