A display panel (1) comprising a body of optical material, the body having at least one optical image recorded therein in an encoded manner, wherein the image is selectively reconstructable and viewable (5, 6, 7) by illuminating the panel (1) using at least one light source (3a, 3b, 3c) under selected illumination conditions, wherein the image is reconstructable and viewable (5, 6, 7) such that at least one first optical property or parameter of the reconstructed image (e.g. its geometry, position in space, colour, its dynamic appearance) is selectable in value from amongst variable values of the at least one first optical property or parameter, or whose value is actively modifiable over time, as a function of or in dependence on the value of at least one second optical property or parameter of the illumination conditions of the at least one light source (e.g. its/their position(s) or spacing(s) relative to the panel (1), its/their colour, brightness/optical intensity, polarisation, direction of light ray propagation, application of a scanning technique to illuminate the panel (1)) which is selectable from amongst variable values thereof or which is actively modifiable in value over time.

A diffractive optical element, such as a holographic plasma lens, can be made by direction two laser beams so that they overlap in a nonlinear material, to form an interference pattern in the nonlinear material. The interference pattern can modify the index of refraction in the nonlinear material to produce the diffractive optical element. The interference pattern can modify the distribution of plasma for the nonlinear material, which can adjust the index of refraction. A third laser beam can be directed through the diffractive optical element to modify the third laser beam, such as to focus, defocus, or collimate the third laser beam.

A method and system for forming a holographic structure in a material. The holographic structure is configured to project a selected target image in the far field under illumination of the holographic structure by a laser. The method calculates a modified design for the holographic structure that encodes a unique identifier within the holographic structure for projecting the target image. The method modifies the material by mapping features corresponding to the modified design into the material so as to form the holographic structure. A basic check of the authenticity of the material is performed by checking whether a projected replica of the target image is as expected. A more detailed check of the authenticity of the material is performed by directly inspecting the features in the holographic structure.

A diffractive optical element, such as a holographic plasma lens, can be made by direction two laser beams so that they overlap in a nonlinear material, to form an interference pattern in the nonlinear material. The interference pattern can modify the index of refraction in the nonlinear material to produce the diffractive optical element. The interference pattern can modify the distribution of plasma for the nonlinear material, which can adjust the index of refraction. A third laser beam can be directed through the diffractive optical element to modify the third laser beam, such as to focus, defocus, or collimate the third laser beam.

A display panel (1) comprising a body of optical material, the body having at least one optical image recorded therein in an encoded manner, wherein the image is selectively reconstructable and viewable (5, 6, 7) by illuminating the panel (1) using at least one light source (3a, 3b, 3c) under selected illumination conditions, wherein the image is reconstructable and viewable (5, 6, 7) such that at least one first optical property or parameter of the reconstructed image (e.g. its geometry, position in space, colour, its dynamic appearance) is selectable in value from amongst variable values of the at least one first optical property or parameter, or whose value is actively modifiable over time, as a function of or in dependence on the value of at least one second optical property or parameter of the illumination conditions of the at least one light source (e.g. its/their position(s) or spacing(s) relative to the panel (1), its/their colour, brightness/optical intensity, polarisation, direction of light ray propagation, application of a scanning technique to illuminate the panel (1)) which is selectable from amongst variable values thereof or which is actively modifiable in value over time.