Michelson Setup Research Articles

Retrieving the axial position of fluorescent light emitting spots by shearing interferometry

A method for the depth-resolved detection of fluorescent radiation based on imaging of an interference pattern of two intersecting beams and shearing interferometry is presented. The illumination setup provides the local addressing of the excitation of fluorescence and a coarse confinement of the excitation volume in axial and lateral directions. The reconstruction of the depth relies on the measurement of the phase of the fluorescent wave fronts. Their curvature is directly related to the distance of a source to the focus of the imaging system. Access to the phase information is enabled by a lateral shearing interferometer based on a Michelson setup. This allows the evaluation of interference signals even for spatially and temporally incoherent light such as emitted by fluorophors. An analytical signal model is presented and the relations for obtaining the depth information are derived. Measurements of reference samples with different concentrations and spatial distributions of fluorophors and scatterers prove the experimental feasibility of the method. In a setup optimized for flexibility and operating in the visible range, sufficiently large interference signals are recorded for scatterers placed in depths in the range of hundred micrometers below the surface in a material with scattering properties comparable to dental enamel.

Surface topography by wavelength scanning interferometry

Parallel and absolute measurement of surface shape using wavelength scanning interferometry has been applied to various objects including diffuse surfaces and milled ones having discontinuities such s steps, dips, and protrusions. We have employed not only the Michelson setup but also the Fizeau one newly introduced. The behaviors of interference signals arising from these objects are experimentally compared. Spiky noises have been observed from the milled surfaces and the defocused diffuse surface. In spite of the noise we succeeded in measuring steps and narrow dips on a mirror and a milled surface, as well as a cylindrical protrusion on a diffuse surface. With a dye laser of tuning range of 4.2 nm we attained the resolution of 39 micrometer within the depth of 3 mm.

Measurement of rotational vibrations using a novel interferometric technique

Interferometric systems for the measurement of rotational vibration have been available for some time, based on the simple Michelson set-up. Both beams must be used to generate the rotation sensitivity and eliminate linear vibration signals. Because both beams impinge on the surface, and are thus drastically attenuated, the interferometric signals is extremely weak, and only truly useful on specially treated surfaces Here we present a system utilising a purpose-built twin interferometer which provides improved sensitivity and, due to the heterodyne configuration, the capability to measure at zero dc rotation with directional information.

Impact of the Sinusoidal Drive on the Instrumental Line Shape Function of a Michelson Interferometer with Rotating Retroreflector

In Fourier spectrometers using the classical Michelson setup, conventionally a plane mirror travels with constant speed to generate an optical pathlength alteration. Recently, different types of Michelson interferometers have been developed that use one or more rotating retroreflectors for pathlength variation. They all exhibit a sinusoidal dependence of the pathlength on time. This paper discusses the effects of the nonlinear mirror motion on the interferogram and the calculated spectrum. The requirements necessary for the acquisition system are deduced, and distortions due to nonideal analog electronics are calculated quantitatively. The investigations concentrate on the influence of a nonconstant electronic transfer function and differences in the delay times of the measurement channel and the reference channel, which generates the sampling pulses. The results are applied to the laboratory model of a Michelson interferometer with rotating reflector (spectral resolution ≈0.5 cm−1). It is proved by measuring the instrumental line shape function (ILS) that there can be compensations for the effects mentioned above, with a residual error of less then 1% in comparison to the results for the ideal ILS.

Polarized picosecond fluorescence measurements of dye molecules with optical upconversion in modified Michelson set-up

The upconversion technique has been extended to become available as a standard detection method for the observation of ultrashort fluorescence decays. Picosecond pulses at high repetition rates are delivered from a commercial Nd:YAG and dye laser system. The experimental arrangement incorporates for the first time polarized fluorescence collection at an angle of 0 degrees in an easily aligned Michelson set-up and a very sensitive low-level photon counting system. Using the ultrashort-lived fluorescence scatterer malachite green as apparatus, function coherence effects are avoided and the fluorescence decay and depolarization are analysed by numerical deconvolution methods. The capabilities of the apparatus are demonstrated with solutions of the dyes DQTCI and oxazine 1.

Optical implementation of the Banyan network

The Banyan networks belongs to the class of log 2 ( N) networks like the perfect shuffle and the crossover network. A technique of implementing the Banyan network with free-space optics is described. The implementation is based on a polarization encoding of the input. Space-variant polarizers like liquid crystal spatial light modulators can be used for this purpose. Two optical systems are described for the implementation of our technique which are based on a Mach-Zehnder setup and a Michelson setup, respectively.

All-fiber interferometer for chromatic dispersion measurements

An all-fiber interferometric method for chromatic dispersion measurements in meter-length single-mode fibers is presented. In a Michelson setup the physical length of a reference fiber was varied so as to obtain adjustable optical delay. Time resolution, ease of manipulation, and mechanical isolation are considerably improved with respect to conventional interferometers. Resolution of group delay measurement and chromatic dispersion over the full 1100-1700-nm spectral range are better than 5 fs and 0.1 ps/nm-km, respectively. >

Achromatic stellar interferometry

One drawback of Michelson's stellar interferometer is due to the fact that the period of the interference fringes is proportional to the wavelength. Hence, in broadband light the fringe contrast is low, or in narrowband light (after filtering) the luminosity is low. We propose a modified stellar interferometer with perfectly achromatic fringes, that has better light efficiency and better signal to noise under most circumstances. To that end, two pieces of grating have to fill the two apertures of Michelson's setup. Achromatic interference fringes occur somewhere along the system axis, where the plus-first diffraction order from one aperture meets the minus-first diffraction order from the other aperture. Laboratory experiments confirm the predicted achromatic performance.