Franco Quercioli

Experimental statistics of fully developed speckle fields by phase-shifting interferometry

Abstract Phase-shifting interferometry techniques are used to directly investigate the first order statistics of real and imaginary parts of fully developed speckle fields. With reference to classic random walk models, the major assumptions and steps leading to the observed distributions are illustrated on experimental data sets.

Digital phase-shifting interferometry applied to partially developed speckle fields

Partially developed speckle fields produced by a weak scatterer are studied with digital phase-shifting interferometry techniques. Data acquisition and processing is described, and laboratory results are presented

Experimental statistics of partially developed speckle fields.

An experimental approach to a partially developed speckle pattern is presented that measures both the amplitude and the phase of the speckle field. With reference to existing models in statistical optics, complex field distribution parameters are evaluated, and mutual relationships are verified.

Monitoring the optical polishing process by computerized microscopy techniques

This work relates to the glass polishing process in optical workshops, classically based on pitch lapping of ground surfaces. The process progressively removes the asperities and lowers the surface toward the bottom of the remaining pits. According to Prestons hypothesis, the polishing rate is proportional to the velocity of the lap and to its pressure on the area of contact. A computerized imaging technique is here reported to monitor the progress of the polishing action. A Nomarski microscope with a 16X objective has been equipped with a TV camera connected to a personal computer. A frame grabber provides image data that are elaborated to work out the surface features. Statistics are obtained on the fractional area covered by the residual pits. Referring to the Prestons hypothesis, the measured parameter is related to the actual finish grade of the surface inspected.

Real-time measurement of optical thickness by three-channel homodyne interferometry

A homodyne interferometer is described, using a He-Ne laser source and working in Twyman- Green configuration. By means of proper retardation plates and polarizing beam splitters, three signals at 90 degree(s) phase lag are made available. Such signals are digitized and fed into a desktop computer. Fitting procedures and computing algorithms are then implemented working out a phase angle; monitoring such a phase provides information on the optical path difference between the two arms of the interferometer. The general features of the approach are reviewed; examples of application are given, monitoring the fine displacement of mechanical parts and measuring the optical thickness variation of a soap film in air.

Speckle-based interferometric technique for surface-finish measurements

After being processed by an optical system, either in reflection or in transmission, a probe wavefront contains information on the induced aberrations that are conveniently reported by interferometry. Yet, the probe beam also includes diffuse light, mostly produced by scattering at the optical surfaces. The actual disturbance that is studied via interferometry is a partially developed speckle field, made of a strong bias phaser plus the weak random contribution due to scattering. The standard deviation of the random contribution, normalized to the modulus of the bias phaser, is assumed as a characteristic parameter of the speckle field. Such a parameter has been measured with digital phase-shift interferometric techniques on a series of selected samples, corresponding to different optical finish. In excess of 120 samples have been studied, referred to a traceable polishing process. The results are interpreted on the basis of available models of polishing mechanisms. Data fitting to the equation of the theory is reported; the results are in fair agreement with the theory.

Phase-shifting speckle interferometry

Phaseshifting interferometry applied to speckle fields is described. Experimental cases of both weak and strong scatterers are investigated. Statistical parameters are sought on timing of the polishing process of optical sample surfaces. 1 .

Laser-Diode Recorded Reflection Holograms Shifted To Visible

The use of a laser diode source in the near-infrared region for making reflection holograms reconstructed in visible light is described. The source coherence function is investigated, and techniques for shrinking the holographic emulsion of silver halide recording materials are reported.

Rainbow Contouring By Holographic Multiplexing

A two-step holographic process is presented where first step is recording of contiguous object slices at correspondingly ordered plate stripes. The second holographic recording is made out of the real pseudoscopic reconstruction after the first hologram. Illumination of the final hologram with a conjugate white light beam produces a rainbow presentation where colors encode the object depth contouring.

Esame ottico dei cannocchiali di Galileo

SUMMARY The results of a series of optical tests recently performed on the Galileos telescopes are reported. In particular, evidence is given of the interferometric quality of the lenses, nearly attaining optical perfection.