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Dändliker, René
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Dändliker, René
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- PublicationAccès libreFrequency-comb-referenced two-wavelength source for absolute distance measurement(2006)
;Schuhler, Nicolas ;Salvadé, Yves ;Lévêque, Samuel; Holzwarth, RonaldWe propose a new tunable laser source concept for multiple-wavelength interferometry, offering an unprecedented large choice of synthetic wavelengths with a relative uncertainty better than 10−11 in vacuum. Two lasers are frequency stabilized over a wide range of frequency intervals defined by the frequency comb generated by a mode-locked fiber laser. In addition, we present experimental results demonstrating the generation of a 90 μm synthetic wavelength calibrated with an accuracy better than 0.2 parts in 106. With this synthetic wavelength we can resolve one optical wavelength, which opens the way to absolute distance measurement with nanometer accuracy. - PublicationAccès libreHigh resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)(2006)
;Scherler, OlivierOne method for locating extrasolar planets is to observe the lateral movement of a star in the sky caused by a planet in orbit around it. In order to detect this displacement, the angular position of the star has to be measured with high accuracy. This technique is called astrometry. The Very Large Telescope Interferometer (VLTI) is operated by the European Southern Observatory and located at the Paranal Observatory in Chile. The purpose of the PRIMA instrument (Phase Referenced Imaging and Micro-arcsecond Astrometry) of the VLTI is to perform high-resolution astrometric measurements and high-resolution imaging of faint stars using white light interferometry, by combining the light collected by two telescopes. In order to allow the detection of extrasolar planets, the astrometric measurement has to be performed with micro-arcsecond accuracy. In astrometric mode the PRIMA instrument observes two targets at the same time: the object of scientific interest, and a bright reference star. The angular position of the science object relative to the reference star is obtained by monitoring the differential optical path travelled by the light of each object in two separate white-light interferometers. The aim of this work was to develop a high-resolution laser metrology based on superheterodyne interferometry, with an accuracy of 5 nm over a differential optical path of 100 mm. Moreover the laser source had to be stabilised on an absolute frequency reference, in order to ensure the long-term stability and calibration required to achieve the target performance. Superheterodyne interferometry allowed the direct measurement of the differential optical path using two heterodyne interferometers working with two different frequency shifts. The differential phase measurement between the two interferometers was obtained by electronic mixing of the two heterodyne signals, leading to the differential optical path needed for the astrometric measurement. - PublicationAccès libreHigh Resolution Interference Microscopy: A Tool for Probing Optical Waves in the Far-Field on a Nanometric Length Scale(2006)
;Rockstuhl, Carsten ;Märki, Iwan ;Scharf, Toralf ;Salt, Martin Guy; High Resolution Interference Microscopy (HRIM) is a technique that allows the characterization of amplitude and phase of electromagnetic wave-fields in the far-field with a spatial accuracy that corresponds to a few nanometers in the object plane. Emphasis is put on the precise determination of topological features in the wave-field, called phase singularities or vortices, which are spatial points within the electromagnetic wave at which the amplitude is zero and the phase is hence not determined. An experimental tool working in transmission with a resolution of 20 nm in the object plane is presented and its application to the optical characterization of various single and periodic nanostructures such as trenches, gratings, microlenses and computer generated holograms is discussed. The conditions for the appearance of phase singularities are theoretically and experimentally outlined and it is shown how dislocation pairs can be used to determine unknown parameters from an object. Their corresponding applications to metrology or in optical data storage systems are analyzed. In addition, rigorous diffraction theory is used in all cases to simulate the interaction of light with the nano-optical structures to provide theoretical confirmation of the experimental results. - PublicationAccès libreMeasuring optical phase singularities at subwavelength resolution(2004)
; ;Märki, Iwan ;Salt, Martin GuyNesci, AntonelloWe will present experimental and theoretical studies of optical fields with subwavelength structures, in particular phase singularities and coherent detection methods with nanometric resolution. An electromagnetic field is characterized by an amplitude, a phase and a polarization state. Therefore, experimental studies require coherent detection methods, which allow one to measure the amplitude and phase of the optical field with subwavelength resolution. We will present two instruments, a heterodyne scanning probe microscope (heterodyne SNOM) and a high resolution interference microscope (HRIM). We will review some earlier work using the heterodyne SNOM, in particular the measurement of phase singularities produced by a 1 µm pitch grating with 10 nm spatial sampling. Using the HRIM we have investigated the intensity and phase distributions (with singularities) in the focal region of microlenses. The measurements are compared with the results calculated by rigorous diffraction theory. - PublicationAccès libreHigh-resolution measurement of phase singularities produced by computer-generated holograms(2004)
;Rockstuhl, Carsten ;Ivanovskyy, Andrey Albert ;Soskin, Marat Samuil ;Salt, Martin Guy; We present measurements of the intensity as well as the phase distribution in the various diffraction orders of computer-generated holograms designed to generate a higher order Gauss–Laguerre beam. For the direct measurement of the phase distribution in the diffraction orders a high-resolution interferometer is used, which allows access to a lateral length scale for the localization of phase singularities below the wavelength. It is experimentally shown that in beams that carry multiple singularities, the dislocations do not degenerate. This effect cannot be seen by analyzing only the intensity distribution of the laser beam. - PublicationAccès librePolarization Optics of Periodic Media(2004)
;Bohley, ChristianThe thesis describes different approaches for the simulation of light propagation in anisotropic media. It will focus, especially, on polarization effects in anisotropic media with periodic structure. The work gives shortly a theoretical background with some essential considerations for polarization optics. This includes Maxwell's equations, the explanation of matrix concepts for optical elements and a mathematical discussion concerning the conditions for a possible separation of problems for two particular orthogonal polarizations. Methods for the simulation of light propagation with application examples for each method are described. The introduced methods will be used to analyze periodic or quasi-periodic structures. The 4x4 matrix method is used for the investigation of the reflection behaviour of cholesteric liquid crystals. Expanding this method by statistical means to inhomogeneous liquid crystals such as polymer-dispersed liquid crystals are investigated. Moreover, a special optimization method for cholesteric Bragg filters is proposed. A space-grid time-domain method is presented and applied to liquid crystal gratings, for which the director configurations are calculated explicitly. The last chapter deals with special phases of chiral nematic liquid crystals: the Blue Phases. The diffraction effects of Blue Phase structures are examined applying a 4x4 matrix method. The method was extended to be applicable to anisotropic crystal problems. The polarization and interference effects are described. Finally, Mueller matrices of the light, which is Bragg reflected by the Blue Phase structures, are calculated and compared with published experimental values for the some components of the Mueller matrices. Additionally, experimental aspects like preparation, polymerization and measurements of Blue Phases are presented and evaluated - PublicationAccès librePropagation of the electromagnetic field in fully coated near-field optical probes(2003)
;Vaccaro, L. ;Aeschimann, L. ;Staufer, U.; Fully metal-coated near-field optical probes, based on a cantilever design, have been studied theoretically and experimentally. Numerical simulations prove that these structures allow nonzero modal emission of the electromagnetic field through a 60-nm-thick metallic layer, that is opaque when deposited on flat substrates. The far-field intensity patterns recorded experimentally correspond to the ones calculated for the fundamental and first excited LP modes. Moreover, this study demonstrates that a high confinement of the electromagnetic energy can be reached in the near-field, when illuminated with radially polarized light. Finally, it was verified that the confinement of the field depends on the volume of the probe apex.