The invention is directed to systems and methods of digital signal processing and in particular to systems and methods for measurements of thermoreflectance signals, even when they are smaller than the code width of a digital detector used for detection. Each of the optical scanners has a reflecting surface that is formed helically around a cylindrical body. During mounting, the slide door is stressed with the spring member toward the position in which the opening is closed by fitting a lower edge of the slide door into the guide portion of the lower half A mounting position of the slide door is retained by holding an end of the slide door facing a direction in which the slide door moves to close the opening. The functionality of the system is accomplished using a multi-pilot system acting on a spool valve that has a pilot piston and at least one stop piston. A write-back path couples the latch ring and first configuration memory.