在多层干涉膜的批量生产中,从一个生产周期到下一个生产周期,保持薄膜的光谱特性的重复性是十分重要的。近年来,研制出很多型式的监控膜厚的自动装置,但工业中用得最多的光学监控方法,都是一个建立在极值法基础上的光度计,经过变换光电信号,有的还经过微分,达到自动监控膜厚的目的。有人曾证明过,在固定波长进行监控,可以借助于附加大小等于极值的偏压,用微分放大器控制,精度可以大大提高。但实现起来,每层都要调节偏压,很困难。最近苏联有人在研制镀冷反光镜的自动 In mass production of multilayer interference films, it is important to maintain the reproducibility of the spectral characteristics of the film from one production cycle to the next. In recent years, many types of automatic devices have been developed to monitor film thickness. However, the most widely used optical monitoring method in the industry is a photometer based on the extremum method. After the photoelectric signal is changed, some are differentiated , To automatically monitor the purpose of film thickness. It has been proven that monitoring at a fixed wavelength can be done with a differential amplifier with the aid of an additional bias voltage equal to the extremum and the accuracy can be greatly improved. However, it is difficult to achieve bias adjustment at each level. Someone in the Soviet Union recently developed a galvanometer mirror automatically