LM-0140 CNC Calibration Extension for LM-0100

Measuring a length is the comparison of an unknown length with a known one. Since 1983 the standard of one meter is defined as the length of the path traveled by light in vacuum during a time interval of 1/299792458 of a second. The effect of this definition is to fix the speed of light (c) in vacuum at exactly 299 792 458 m/s.
If we consider the relation ν=c/λ where ν denotes the frequency and λ the wavelength of the light radiation it becomes clear that in case the frequency of the radiation is known the wavelength λ is known as well. If the used light source has a known and constant frequency it represents a secondary standard of the meter. Preferentially a laser can fulfill the demand of a defined and stable frequency. In practice HeNe-Laser systems are used which frequency is stabilized using optical transitions of the Iodine 127 isotope. The uncertainty of the frequency stabilization by using this method is better than 1x10E-12. For technical applications like calibrating CNC machines an uncertainty of 1x10E-7 is sufficient. This value corresponds to an accuracy of 0.1 µm per one meter. A HeNe-Laser without any frequency stabilization means has a fairly good uncertainty of 1x10E-6 and will be used in this experiment.
By using the Michelson interferometer we count how many λ/2 bright/dark transition (fringe) occur along the distance to be measured. The movement will be done by using a computer controlled motorized translation stage with built-in incremental encoder. The traveled distance is compared with the result of the Michelson interferometer which represents the standard of the meter.