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Measurements of Residual Reflectivity and Wavelength of Coated Laser Diodes
Růžička, Bohdan ; Lazar, Josef ; Wilfert, O.
This contribution presents experimental results obtained by deposition of double-layer system made by means of electron-beam vacuum evaporation technique. We oriented our effort to short-wavelength 633 - 635 nm laser diodes. These devices are emitting close to the wavelength of traditional He-Ne lasers with an intention to use them in extended-cavity laser design for metrological purposes. The resulting reflectivities were evaluated by measuring a testing plate of GaAs and by measuring a "modulation depth" of a coated diode emission spectra. Our best results were reflectivities well below 10 -4 and the repeatibility of the deposition process in a range not exceeding 2x10 -4 .
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Saddle Coil Magnetic Field Calculations
Bělohrad, David ; Kasal, Miroslav
The atricle describes basic magnetic field calculations of the RF coils in MRI. In the first part of the article basic elements are discussed, the calculations in the center of the coil are shown. In the next section the model for entire-magnetic field calculations is made and some results of calculations are presented. In the conclusion the theory is partially expanded to the RF Saddle coils, which are able to work on higher resonant frequencies.
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Phase Noise Measurement
Viščor, Ivo ; Halámek, Josef
The analysis of the phase noise is presented. The phase fluctuation can be described of either standard deviation of the phase or time jitter or in detail as signal's spectrum. The digital receiver is proposed for the phase noise measurements.
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