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All About Wave Equations
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
Interferometers are widely used in science and industry for the measurement of small displacements, refractive index changes and surface irregularities. In an interferometer, light from a single source is split into two beams that travel different optical paths, then combined again to produce interference. The resulting interference fringes give information about the difference in optical path length. In analytical science, interferometers are used to measure lengths and the shape of optical components with nanometer precision; they are the highest precision length measuring instruments existing. In Fourier transform spectroscopy they are used to analyze light containing features of absorption or emission associated with a substance or mixture. An astronomical interferometer consists of two or more separate telescopes that combine their signals, offering a resolution equivalent to that of a telescope of diameter equal to the largest separation between its individual elements.
Special Topics
Published in N.V. Joshi, Photoconductivity, 2017
The basic principle of Fourier transform spectroscopy is based on the fact that in a double-beam interferometer the intensity of the central fringe obtained at the output is the Fourier transform of the incident optical power spectrum [6,7]. The fundamental equation on which this method is based can be written as [6] f(ν)=∫0∞[I(x)−I(0)2]cos2πνxdx
Rotational spectroscopy of rare iron monoxide isotopologues: A mass-independent analysis
Published in Molecular Physics, 2020
Björn Waßmuth, Alexander A. Breier, Mattia Melosso, Guido W. Fuchs, Thomas F. Giesen
First pure rotational spectra in the mm-wave region were recorded by Endo et al. [23]. Their observations revealed transitions of the three lowest spin states (, and ). Kröckertskothen et al. [24] extended these data using microwave optical double resonance spectroscopy. Taylor et al. [17] measured the ground state Λ-doubling in the and components by means of Fourier transform spectroscopy. Pure rotational data of all five spin states of the main isotopologue, , including Λ doubling and transitions in some spin states of have been measured by Allen et al. [25]. From optical Stark spectroscopy the permanent electric dipole moments and were derived [26].
Principle of a two-output-difference interferometer for removing the most important interference distortions
Published in Journal of Modern Optics, 2018
Qinghua Yang, Lixin Liu, Pei Lv
A two-output-difference interferometer for getting distortion-free interferograms was merely investigated theoretically, and it has two main features. First of all, the resulting interferogram is made up of the difference between the signals of the two detectors. Moreover, the modulated signals at each output have the same amplitude and opposite phases. As a consequence, the recorded interferogram is free from the most important intensity distortions caused by the nonlinear detectors. Secondly, it has neither tilt nor shearing problems, since it uses two corner-cube mirrors fixed back-to-back as a single moving element. Furthermore, the optical path difference is four times the displacement of the moving element. The interferometer is not restricted to the nonlinear effects of the only detectors but also of the entire electronic system which amplifies each detector signal. The benefit of the interferometer enables it to be applicable to Fourier transform spectroscopy.
Joint spectral characterization of photon-pair sources
Published in Journal of Modern Optics, 2018
Kevin Zielnicki, Karina Garay-Palmett, Daniel Cruz-Delgado, Hector Cruz-Ramirez, Michael F. O’Boyle, Bin Fang, Virginia O. Lorenz, Alfred B. U’Ren, Paul G. Kwiat
Another possibility is to use Fourier transform spectroscopy to measure frequency in the time domain, as in Section 2.3. This exploits a self-interference effect and the property that the extremely short (femtosecond) time regime of the electric field oscillations is easily accessible by an optical delay in a bulk optical medium. This provides a useful characterization of the joint spectrum, but is not an ideal measurement; it is not particularly simple due to the required scanning interferometers and the Fourier transform that relates the time-domain measurement to the desired frequency-domain result. It is also relatively slow, though Section 2.3.2 describes a speed-up that makes the measurement more practical.