Light modulation element and information recording medium

An information recording medium comprising:

• a light modulation element comprising:
• a factor element that modulates a phase of incident reproduction light so as to reproduce a light image, the factor element having an uneven surface with a different height of three or more steps,
• the factor element having a first-order maximum diffraction efficiency in a wavelength band from 380 nm to 780 nm of first-order diffracted light with a full width at half maximum of 200 nm or less, and the factor element having a negative first-order maximum diffraction efficiency in a wavelength band from 380 nm to 780 nm of negative first-order diffracted light with a full width at half maximum of 200 nm or less,
• the factor element being configured to:
• reproduce a first-order diffracted light image with the first-order diffracted light;
• and
• reproduce a negative first-order diffracted light image with the negative first-order diffracted light,
• wherein a wavelength showing the first-order maximum diffraction efficiency is different from a wavelength showing the negative first-order maximum diffraction efficiency,
• wherein the first-order diffracted light image and the negative first-order diffracted light image represents information based on at least one of a letter, a symbol, and a picture,
• the first-order diffracted light image and the negative first-order diffracted light image are point-symmetric about the incident reproduction light to each other, and
• the factor element is a Fourier transform hologram, and
• wherein a difference between the wavelength showing the first-order maximum diffraction efficiency and the wavelength showing the negative first-order maximum diffraction efficiency is 100 nm or less.