Holographic recording method detecting displacement of a holographic recording medium, and recording and reproduction apparatus

A holographic recording and reproduction apparatus, comprising:

• a first detector configured to generate a displacement signal by detecting a displacement of a holographic recording medium in which an information item is recorded in a form of a hologram by interference of information light and reference light, the information light being emitted by a coherent light source and including the information item to be recorded, the reference light and the information light being the same wavelength;
• a calculator configured to calculate a frequency distribution information item of first sampling values of the displacement signal, by sampling the displacement signal at a first interval time to obtain the first sampling values and assigning frequencies to classes which correspond to the first sampling values, the classes being a plurality of ranges divided at first intervals;
• a determination unit configured to determine an allowable displacement range as an amplitude range of a displacement of the displacement signal based on the frequency distribution information item;
• and
• an exposure control unit configured to perform an exposure control operation that, if a second sampling value which is a latest sampling value of the displacement signal falls within the allowable displacement range, records the information item in the holographic recording medium, and if the second sampling value of the displacement signal falls outside the allowable displacement range, blocks or reduces at least one of the information light and the reference light to a light intensity with which the information item is not recorded in the holographic recording medium.