Stretchable and conformable optical devices open very exciting perspectives for the fabrication of systems incorporating diffracting and optical power in a single element and of tunable plasmonic filters and absorbers. The use of nanocomposites obtained by inserting metallic nanoparticles produced in the gas phase into polymeric matrices allows to effectively fabricate cheap and simple stretchable optical elements able to withstand thousands of deformations and stretching cycles without any degradation of their optical properties. The nanocomposite-based reflective optical devices show excellent performances and stability compared to similar devices fabricated with standard techniques. The nanocomposite-based devices can be therefore applied to arbitrary curved non-optical grade surfaces in order to achieve optical power and to minimize aberrations like astigmatism. Examples discussed here include stretchable reflecting gratings, plasmonic filters tunable by mechanical stretching and light absorbers.
We describe the method of Heterodyne Near Field Speckles (HNFS) for the characterization of spatial and temporal coherence of radiation. The method relies on the statistical properties of the speckle field produced by spherical particles randomly distributed and suspended in a fluid. We report preliminary results obtained with broadband light sources. We discuss the results obtained with the Self-Amplified Spontaneous Emission free electron laser SPARC LAB. This method will enable to calibrate and realize a diagnostics for the X-ray, broadband betatron radiation emitted in laser-plasma accelerators.
We present a novel technique for particle sizing, based on recent studies about near field speckles, that is simpler than the existing light scattering methods. We first recall the results about the so called <i>near field scattering </i>(NFS) condition for the light scattered by a disordered sample, discussing the main features of this remarkable region of the scattered light. Then we present the two standard configurations (homodyne and heterodyne NFS) adopted for carrying out NFS measurements. The two configurations are critically discussed and the great advantages of the heterodyne scheme are
emphasized, such the extremely simple layout, the rigorous subtraction of stray light and the almost zero alignment
requirements. Results obtained with suspensions of calibrated
polystyrene spheres are presented and discussed.
3-D holographic images of extended diffusing objects are simultaneously recorded and reconstructed by optical cross- correlation in a second-order non-linear crystal. An interaction geometry in which the phase-matched object and reference fields propagate slightly non-colinearly is particularly convenient to obtain these Second Harmonic Generated (SHG) holograms.
A method of wavefronts' cross-correlation by means of Second Harmonic Generated Hologram (SHG hologram) is considered. According to this method, the interference pattern of an object and reference waves is recorded in a nonlinear light-sensitive material using its second order nonlinearity. The SHG hologram generates a wave that forms the reconstructed image of the object, the frequency of the reconstructed wave being doubled. An expression that describes the electrical field of the reconstructed wave is deduced. It is suggested to use the transforming properties of the SHG hologram for constructing the network of changeable interconnection lines which operates on the principle 'light is controlled by light'. The experiment has confirmed the ability of the SHG hologram of forming high quality images of arbitrary objects. The ways of overcoming the effect of doubling the frequency of the light after each act of a signal transformation are considered. The theory has shown that by using the effect of 'down-conversion' it is possible either to return the frequency of the signal to its initial value or to sustain the value of the frequency at the constant level.
A new method of wavefronts' cross-correlation by means of so-called Second-Harmonic-Generated Hologram (SHG hologram) is considered. According to this method the interference pattern of an object wave and a reference wave is recorded in nonlinear light-sensitive material using its second order nonlinearity. The SHG hologram generates the wave that forms the reconstructed image of the object without time delay in the moment when interfering wavefronts intersect the image of the object without time delay in the moment when interfering wavefronts intersect the light-sensitive material, the frequency of the reconstructed wave being doubled in comparison with the frequency of the recorded waves. The expression that describes the electrical field of the reconstructed wave is deduced. Basing on this expression the methods for the construction of the image generated by SHG hologram are developed. It is suggested to use the transforming properties of the SHG hologram for constructing the network of changeable interconnection lines, which operates on the principle `light is controlled by light'. The experiment on the recording of the SHG hologram was carried out. The SHG hologram was recorded in BBO I crystal with the help of Nd:YAG pulse laser. The experiment has confirmed the ability of the SHG hologram to form high quality images.