Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. Present technology allows for recording binary CGHs. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. Opaque at rest, this plate becomes transparent when it is illuminated with visible light. We have successfully recorded the very first amplitude grayscale Fresnel CGH, with a contrast greater than 50, which was reconstructed with a high fidelity in shape, intensity, size and location. We propose a new Fourier CGH coding scheme leading to a quantification exceeding 1000 within a smaller cell size of 2x2 pixels. This code has been implemented for the BATMAN-instrument logo for visiting very different spatial frequencies. The CGH is recorded with our DMD-based set-up, leading to a 1000x1000 pixels hologram written on a photochromic plate. The reconstruction of the recorded images with a 632.8nm He-Ne laser beam and an imaging lens leads to images with a perfect fidelity in shape and intensity, for any single pixel of the original object. Our proposed code exhibits a much higher resolution, a better compacity and an increased throughput, in comparison with the current Fourier CGHs. These results reveal the high potential of this method for generating programmable/rewritable CGHs.

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. Present technology allows for recording binary CGHs. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. Opaque at rest, this plate becomes transparent when it is illuminated with visible light. We have successfully recorded the very first amplitude grayscale Fresnel CGH, with a contrast greater than 50, which was reconstructed with a high fidelity in shape, intensity, size and location.We propose a new Fourier CGH coding scheme leading to a quantification exceeding 1000 within a smaller cell size of 2x2 pixels. This code has been implemented for the BATMAN-instrument logo for visiting very different spatial frequencies. The CGH is recorded with our DMD-based set-up, leading to a 1000x1000 pixels hologram written on a photochromic plate. The reconstruction of the recorded images with a 632.8nm He-Ne laser beam and an imaging lens leads to images with a perfect fidelity in shape and intensity, for any single pixel of the original object. Our proposed code exhibits a much higher resolution, a better compacity and an increased throughput, in comparison with the current Fourier CGHs.These results reveal the high potential of this method for generating programmable/rewritable CGHs.

Computer generated holograms (CGHs) are powerful optical elements used in many fields, such as wavefront shaping, quality testing of complex optics, and anti-counterfeiting devices.The Lee algorithm is the most used to generate binary amplitude Fourier holograms.Grayscale CGHs are known to give a higher reconstruction quality than binary holograms, but they usually require a cumbersome production process.A very simple and straightforward method of manufacturing rewritable grayscale CGHs is proposed here by taking advantage of two key components: a digital micro-mirror device (DMDs) and a photochromic plate.An innovative algorithm, named Island algorithm, able to generate grayscale amplitude Fourier CGHs, is reported and compared with the standard Lee approach, based on 9 levels.A crucial advantage lies on the fact that the increase or decrease of the quantification does not affect the spatial resolution.In other words, the new coding leads to a higher spatial resolution (for a given CGH size) and a reconstructed image with an order of magnitude higher contrast with respect to the classical Lee-coded hologram.In order to show the huge potential of our approach, a 201 level Island hologram is designed, produced and reconstructed, pushing the contrast to values higher than 10 4 .These results reveal the potential of our process as well as our algorithm for generating programmable grayscale CGHs.

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. We propose a Digital Micromirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs. A new Fourier CGH coding scheme, the Island algorithm, is proposed, with a quantification exceeding 1000 within smaller cell size of 2x2 pixels. An hologram has been calculated, recorded, reconstructed and tested successfully: the reconstructed image exhibits a perfect fidelity in shape and intensity, with a much higher resolution, a better compacity and an increased throughput. These results reveal the high potential of this method for generating programmable/rewritable CGHs.

Photochromic materials based on diarylethenes show strong modulation of optical properties such as absorption and refractive index. Thin film of these materials can be obtained by spin coating onto a glass substrate, in different geometries and absorption properties, depending on dye concentration. An optical density (OD) modulation in the visible of the order of 1-3 is obtained. These films are exploited in many optical applications such as Focal Plane Masks (FPMs) for astronomical purpose or Computer Generated Holograms (CGHs). In respect to traditional devices, masks and CGHs based on photochromic materials are easy and fast to be produced and can be rewritten several times.

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing, including aspherical and free-form optics. Today, CGHs are recorded directly with a laser or intermediate masks, allowing only the realization of binary CGHs; they are efficient but can reconstruct only pixilated images. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. The DMD is composed of 2048x1080 individually controllable micro-mirrors, with a pitch of 13.68 mu m. This is a real-time reconfigurable mask, perfect for recording CGHs. The photochromic plate is opaque at rest and becomes transparent when it is illuminated with visible light of suitable wavelength. We have successfully recorded the very first amplitude grayscale CGH, in equally spaced levels, so called stepped CGH. We recorded up to 1000x1000 pixels CGHs with a contrast greater than 50, using Fresnel as well as Fourier coding scheme. Fresnel's CGH are obtained by calculating the inverse Fresnel transform of the original image at a given focus, ranging from 50cm to 2m. The reconstruction of the recorded images with a 632.8nm He-Ne laser beam leads to images with a high fidelity in shape, intensity, size and location. These results reveal the high potential of this method for generating programmable/rewritable grayscale CGHs, which combine DMDs and photochromic substrates.

Diarylethenes are P-type photochromic systems showing reversible light-induced modulation of optical properties, e.g., transmittance and refractive index, in the visible and near infrared regions. Transmittance can be progressively tuned according to the illumination dose, and the pattern written and erased several times with light. We demonstrated binary Computer Generated Holograms based on of photochromic materials, to be used as adaptable reference surfaces in interferometric tests. We encoded by Direct Laser Writing binary amplitude Fresnel Zone Plates into photochromic substrates and successfully tested them into an interferometric setup. More recently, we exploited the non-threshold behavior of photochromic materials to encode grayscale CGHs, which give a better wavefront reconstruction than binary holograms. We propose to use a device based on a Digital Micro-mirror Device as a real-time reconfigurable mask. We recorded for the first time amplitude grayscale CGHs and reconstructed them with high fidelity in shape, intensity and size.

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. Present technology allows for recording binary CGHs. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. Opaque at rest, this plate becomes transparent when it is illuminated with visible light of suitable wavelength. We have successfully recorded the very first amplitude grayscale CGH, with a contrast greater than 50, which was reconstructed with a high fidelity in shape, intensity, size and location. These results reveal the high potential of this method for generating programmable/rewritable grayscale CGHs, which combine DMDs and photochromic substrates.

Computer Generated Holograms (CGHs) are useful for wavefront shaping and complex optics testing, including aspherical and free-form optics. Today, CGHs are recorded directly with a laser or intermediates masks but allows only recording binary CGHs; binary CGHs are efficient but can reconstruct only pixilated images. We propose to use a Digital Micro-mirror Device (DMD) for writing binary CGHs as well as grayscale CGHs, able to reconstruct fulfilled images. DMD is actually studied at LAM, for generating programmable slit masks in multi-object spectrographs. It is composed of 2048x1080 individually controllable micro-mirrors, with a pitch of 13.68 μm. This is a real-time reconfigurable mask, perfect for recording CGHs. A first setup has been developed for hologram recording, where the DMD is enlightened with a collimated beam and illuminates a photosensible plate through an Offner relay, with a magnification of 1:1. Our set up resolution is 2-3 μm, leading to a CGH resolution equal to the DMD micro mirror size. In order to write and erase CGHs during test procedure or on request, we use a photochromic plate called PUR-GD71-50-ST developed at Politecnico di Milano. It is opaque at rest, and becomes transparent when it is illuminated with visible light, between 500 and 700 nm; then it can be erased by a UV flash. We choose to code the CGHs in equally spaced levels, so called stepped CGH. We recorded up to 1000x1000 pixels CGHs with a contrast greater than 50, knowing that the material is able to reach an ultimate contrast of 1000. A second bench has also been developed, dedicated to the reconstruction of the recorded images with a 632.8nm He-Ne laser beam. Very faithful reconstructions have been obtained. Thanks to our recording and reconstruction set-ups, we have been able to successfully record binary and stepped CGHs, and reconstruct them with a high fidelity, revealing the potential of this method for generating programmable/rewritable stepped CGHs on photochromic materials.