A heater for a window of an optical gas sensor is provided. In an illustrative example, a first sensing vector is analyzed to determine whether it is suitable, within given threshold conditions, for use in cardiac event detection and analysis. 4 inches from an object holder; and a zoom optical system that is connected to the scanning optical system such that the light generated by the laser passes first through the scanning optical system, then through the zoom optical system, and is then imaged through the objective onto the object. The lapping step carries out polishing based on each output value of the reproducing-element polish amount detecting sensor and the recording-element polish amount detecting sensor.