Magneto-optical Kerr effect measurement in ultrafast Sagnac interferometry using the Jones matrix approach
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Abstract:
We report the Jones matrix formalism of the magneto-optic Kerr effect (MOKE) for ferromagnets using an ultrafast Sagnac interferometer. Compared to the time-resolved MOKE instrument, the Sagnac interferometer has the advantage of obtaining the real and imaginary parts of the differential MOKE signal as well as the differential reflectivity and the lattice displacement at the same time. In addition, a simple method to obtain the static values of Kerr rotation and ellipticity is presented.Keywords:
Magneto-optic Kerr effect
Sagnac effect
A Sagnac interferometer (SI) has been constructed with a mode-locked Nd3+:YAG laser as its source. The advantages in pulsed laser interferometry of using a SI over a Mach-Zehnder interferometer are analyzed. The autostability property of SI is experimentally demonstrated. Applications of an SI to light-induced index of refraction change measurements and to the picosecond optical switching are discussed. Experimental results are presented.
Sagnac effect
Picosecond
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We proposed a novel biased optical Kerr gated imaging (BOKGI) method for ultrafast imaging. The imaging performance of the BOKGI system has been investigated. Experimental results showed that by using the BOKGI, the high spatial frequency components of the detected object could be effectively retrieved, which are often filtered by the photo-induced soft aperture in a conventional OKGI system. Comparing with the conventional OKGI method, the BOKGI method could enhance the sharpness of images and provide a higher spatial resolution of the imaging system. In addition, the influence of the biased angle on the BOKGI performance has been also investigated.
Spatial frequency
Aperture (computer memory)
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We describe a time-division interferometer based on the Sagnac geometry for monitoring ultrafast changes in the real and the imaginary components of the refractive index as well as phase changes that are due to surface displacement. Particular advantages of this interferometer are its simple common-path design and operation at normal incidence with a microscope objective for both pumping and probing. Operation is demonstrated by detection of temperature changes and coherent phonon generation in a gold film.
Sagnac effect
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A 3-D Sagnac interferometer can null out light from an on-axis source achromatically. The 3-D Sagnac interferometer can make stable and achromatic pi phase shifts, because it has a common path structure. The achromaticity of the interferometer is theoretically proved by Jones calculus. The experimental setup is constructed, and its nulling characteristics are measured to be about 10(-6) at 5 lambda/d for green (lambda=532 nm) and red (lambda=633 nm) laser light simultaneously. This interferometer would be very useful for the direct detection of faint extrasolar planets.
Achromatic lens
Coronagraph
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We describe a beam-deflection technique based on the ultrafast electronic Kerr effect for measuring the duration of ultrashort laser pulses in a wide spectral range. Using this method, which provides the third-order intensity correlation function, we have measured subpicosecond KrF laser pulses. The results are in good agreement with the Kerr-shutter autocorrelation measurement.
Picosecond
Extreme ultraviolet
Ultraviolet
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We discuss fundamental aspects of laser-induced ultrafast demagnetization probed by the time-resolved magneto-optical Kerr effect (MOKE). Studying thin Fe films on MgO substrate in the absence of electronic transport, we demonstrate how to disentangle pump-induced variations of magnetization and magneto-optical coefficients. We provide a mathematical formalism for retrieving genuine laser-induced magnetization dynamics and discuss its applicability in real experimental situations. We further stress the importance of temporal resolution achieved in the experiments and argue that measurements of both time-resolved MOKE rotation and ellipticity are needed for the correct assessment of magnetization dynamics on sub-picosecond timescales. The framework developed here sheds light onto the details of the time-resolved MOKE technique and contributes to the understanding of the interplay between ultrafast laser-induced optical and magnetic effects.
Magnetization dynamics
Magneto-optic Kerr effect
Picosecond
Temporal resolution
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Magneto-optic Kerr effect
Spin wave
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A method for characterizing the phase response of spatial light modulators (SLMs) by using a Sagnac interferometer is proposed and demonstrated. The method represents an improvement over conventional diffraction-based or interferometric techniques by providing a simple and accurate phase measurement while taking advantage of the inherent phase stability of a Sagnac interferometer. As a demonstration, the phase response of a commercial liquid crystal on a silicon SLM is characterized and then linearized by using a programmable lookup table. The transverse phase profile over the SLM surface is also measured.
Spatial light modulator
Sagnac effect
Spatial frequency
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We describe a novel feedback interferometer for real-time, unambiguous measurement of surface profiles that consists of a polarization Sagnac interferometer and an optically addressed phase-only spatial light modulator. In this system the output intensity from the Sagnac interferometer is optically fed back to the phase modulator placed in one arm of the interferometer, which produces a sawtooth fringe intensity profile (instead of the conventional cosinusoidal one) that is directly and unambiguously related to the surface profile. Preliminary experimental results demonstrate the feasibility of applying this system to surface-profile measurement.
Sawtooth wave
Sagnac effect
Intensity interferometer
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Magneto-optic Kerr effect
Magneto
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