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In the fabrication of planar diffraction gratings, the geometric shape of amplitude modulation profile and the refractive index, as well as the spatial frequency, are the parameters that determine the value of the diffraction efficiency and the number of diffracted orders that are generated, when the periodic structures are illuminated.
The spatial shape of the Bragg plane profiles is related to the nonlinear responses of the periodic structure, and therefore is responsible for obtaining a high number of diffraction orders. In a holographic grating fabricated with a single exposure, all Bragg planes are identical and have the same geometric profile. In this work we make the diffraction grating plane by plane, modifying the geometry and amplitude of each one of the Bragg planes.
To obtain the grating, we record the intensity distribution generated by a Gaussian beam, in an ultrafine-grained emulsion. The optical system is composed of a 405 nm laser and a 50x LWD objective, as well as an automatic mechanical displacement system that allows us to move the irradiation plane every 5 microns, as well as displacement speeds of 15 mm/s. in this way, we can store in the photosensitive medium the Bragg planes, formed by straight lines of different width and depth. The length of each line is 20 millimeters, and its width has varied between 1.4 and 2.5 microns, depending on the focusing intensity and displacement speed, as well as the developer used. By varying the focal plane of the Gaussian beam, it is possible to generate profiles with different geometries.
With this technique, diffraction gratings of 20 lines per millimeter have been obtained, allowing a high number of diffracted orders to be generated. BB450 holographic emulsion developed with AAC has been used as photosensitive medium. The images obtained by digital holographic microscopy are presented, reaching profiles of the exposed area
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