Accurate measurement of coating thickness for alkali vapor cells based on frustrated total internal reflection

For the accurate measurement of coating thicknesses for alkali vapor cells in atomic spinning devices, a measurement method based on Frustrated Total Internal Reflection (FTIR) was proposed. A coating thickness measuring system was established and experimental tests were performed. The phenomenon of FTIR and the principle of coating thickness measurement based on the FTIR were analyzed. And the main factors impacting the measuring accuracy of the system were analyzed and several solutions were given. Furthermore, the performance of the system was evaluated by analyzing and simulating the effects of the wavelength fluctuation, change of laser incident angle, and other inaccurate refractive indexes on the measured results. Finally, the thickness measuring experiment using the system and a check experiment using a film analyzer were carried out for the coating sample. Experimental results indicate that data from the FTIR system generally have a deviation about 2.6 nm. But the system can measure coating thickness exactly with a precision about 1 nm after the deviation compensated, which can satisfy the requirement of evaluation of coating qualities for alkali vapor cells under high stability and reliability.