The advance of techniques of reflectivity measurement

The development of techniques of reflectivity measurements is reviewed and analyzed. Based on the measurement principles,the techniques can be divided into two types.One is single-reflectance,double-reflectance and multi-reflectance on the sample.The other is other measurement based on resonator's characteristics,such as optical cavity decay time,cavity ring-down spectroscopy,spherical cavity optical delay lines,the fineness of the resonator,and the loss compare between two active resonators.Their advantages and disadvantages,in particular,their measurement errors are discussed. Some current hot spots and future directions are analyzed.