No abstract

The development and the performance of a portable holographic refractometer prototype for liquid measurement employing multimode diode lasers with emission centered at 662 nm as light sources is reported. Due to the multiwavelength character of the holographic recording, a synthetic wavelength was generated, and the diffracted wave intensity was thus modulated as a function of the optical path difference between the reference and the object beams. The transparent test cell containing the liquid was placed at the reference-beam arm of the optical setup, while the contour interferogram generated on the holographic image of a flat object was used for fringe counting. A change L on the liquid column length is proportional to the p running fringes on the object image, and from this relation the refractive index of the test liquid was obtained. The holograms were recorded on a photorefractive Bi 12 TiO 20 crystal whether using a single multimode diode laser or by combining two diode lasers. In the latter configuration the synthetic wavelength can be varied in order to enhance the measurement sensitivity and/or to allow the analysis of turbid liquids. The size of the whole prototype is 54 × 22 × 14 cm 3 . The refractive indexes of ethanol/water mixtures with different concentrations were measured, as well as the NaCl concentrations in aqueous solutions were determined upon comparison with an empirical curve. In both cases the results were compared with the ones obtained through an Abbe refractometer.

Ultraviolet-light-induced near-infrared photorefractivity and two-color holography in highly Mg-doped LiNbO 3Abstract. Refractive and profilometric measurements of lenses were performed through holography with a photorefractive Bii2TiO20 crystal as the recording medium. Two properly aligned diode lasers emitting in the red region were employed as light sources. Both lasers were tuned in order to provide millimetric and sub-millimetric synthetic wavelengths. The surfaces of the test lens were covered by a 25-|im opaque plastic tape in order to allow the lens profilometry upon illuminating them with a collimated beam. The resulting holographic images appear covered by interference fringes corresponding to the wavefront geometry of the wave scattered by the lens. For refractive index measurement a diffusely scattering flat surface was positioned behind the uncovered lens which was also illuminated by a plane wave. The resulting contour interferogram describes the form of the wavefront after the beam traveled back and forth through the lens. The fringe quantitative evaluation was carried out through the four-stepping technique and the resulting phase map and the Branch-cut method was employed for phase unwrapping. The only non-optical procedure for lens characterization was the thickness measurement, made by a dial caliper. Exact ray tracing calculation was performed in order to establish a relation between the output wavefront geometry and the lens parameters like radii of curvature, thickness and refractive index. By quantitatively comparing the theoretical wavefront geometry with the experimental results relative uncertainties bellow 3% for refractive index and 1 % for focal length were obtained.