Light guide element comprising a diffraction element having a cholesteric liquid crystal layer with a pitch gradient

A light guide element comprising:

• a light guide plate;
• and
• a diffraction element that is disposed on a main surface of the light guide plate,
• wherein the diffraction element includes a liquid crystal layer that is formed of a liquid crystal composition including a liquid crystal compound and has a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction,
• a refractive index of the light guide plate is 1.70 or higher,
• in a case where the refractive index of the light guide plate is represented by nd and a refractive index of the liquid crystal layer is represented by nk,
• nk−nd≥0
• is satisfied,
• the liquid crystal layer is a cholesteric liquid crystal layer obtained by immobilizing a cholesteric liquid crystalline phase,
• the cholesteric liquid crystal layer is a pitch gradient layer in which a helical pitch changes in a thickness direction, and
• in a main surface of the liquid crystal layer in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating in at least one in-plane direction, in a case where a length over which the direction of the optical axis of the liquid crystal compound rotates by 180° is set as a single period Λ, a helical pitch on one surface side of the pitch gradient layer is represented by P1, and a helical pitch on the other surface side of the pitch gradient layer is represented by P2,
• P1<Λ<P2
• is satisfied.