True colour Denisyuk-type hologram recording of diffusing objects in Bayfol® HX 102 self-developing photopolymer has been studied. In a first stage, monochromatic Denisyuk holograms of a standard white diffuser (Spectralon) have been recorded using lasers with wavelengths 442, 532 and 633 nm to determine the optimum exposure that gives maximum efficiency. The recording of holograms from a diffusing object has the particularity that intermodulation noise due to interference between waves arriving from different object points reduces effective index modulation. A maximum effective efficiency of 80% has been reached for monochromatic recording. In a second stage, a set of experiments has been carried out to determine the adequate relation of exposure for the recording of a Denisyuk hologram of the standard white diffuser with the three lasers simultaneously to get the maximum efficiency for each wavelength. With the determined optimal exposure, a hologram of a polychromatic diffusing object has been recorded, obtaining a good visual coincidence between hologram and original object.
The use of volume and phase holographic elements in the design of photovoltaic solar concentrators has become very popular as an alternative solution to refractive systems, due to their high efficiency, low cost and possibilities of building integration. Angular and chromatic selectivity of volume holograms can affect their behavior as solar concentrators. In holographic lenses, angular and chromatic selectivity varies along the lens plane. Besides, considering that the holographic materials are not sensitive to the wavelengths for which the solar cells are most efficient, the reconstruction wavelength is usually different from the recording one. As a consequence, not all points of the lens work at Bragg condition for a defined incident direction or wavelength. A software tool that calculates the direction and efficiency of solar rays at the output of a volume holographic element has been developed in this study. It allows the analysis of the total energy that reaches the solar cell, taking into account the sun movement, the solar spectrum and the sensitivity of the solar cell. The dependence of the recording wavelength on the collected energy is studied with this software. As the recording angle is different along a holographic lens, some zones of the lens could not act as a volume hologram. The efficiency at the transition zones between volume and thin behavior in lenses recorded in Bayfol HX is experimentally analyzed in order to decide if the energy of generated higher diffraction orders has to be included in the simulation.
We have developed simulation software by Matlab (MathworksInc.) with a graphical interface designed for non-expert users. This simulator allows you to complete the process of subjective refraction starting from the aberrometry of the patients and analyse the influence of different factors during the exam. In addition to explain the graphical interface and its working, we show two examples about a complete process of subjective refraction with the influence of high order aberrations and without them showing the retinal image obtained in each step of the refraction process. When the Jackson Cross-Cylinder technique is made with this software, it becomes clear the difficulty of chosen between two images when high order aberrations are present. Therefore, the variability of response during the refraction can be a problem when the examiner has to reach an adequate optical prescription.
In this work we design and construct a pulse compressor with volume transmission holographic gratings, to compensate
the second order dispersion in femtosecond laser pulses emitting at 794 nm with a spectral broadband of 10 nm. The
gratings (730 lines/mm) are recorded in PFG-04 dichromated gelatine emulsion with a wavelength of 532 nm, reaching
enough index modulation to use the gratings illuminated with 800 nm light source with high efficiency (around 80% of
efficiency in each grating). This efficiency is expected to be increased with an antireflection coating. We measure the
factor of compression as a function of the grating distance using an autocorrelator, finding a good agreement with
theoretical curve. A dispersed pulse (580 fs) is reduced to the bandwidth limited value of 106 fs with the grating pair
separated by 27 mm.