The Experts below are selected from a list of 101421 Experts worldwide ranked by ideXlab platform
Takeshi Yasui - One of the best experts on this subject based on the ideXlab platform.
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Interferometric Terahertz Wavefront Analysis
IEEE Journal of Selected Topics in Quantum Electronics, 2017Co-Authors: Emmanuel Abraham, Takayuki Ogawa, Mathilde Brossard, Takeshi YasuiAbstract:Wavefront characterization of terahertz beams is useful for various applications such as terahertz spectroscopy and imaging. In this paper, we report on the aberration measurement of a terahertz beam issued from a quantum cascade laser. By using a terahertz camera and a two-wave noncommon path interferom-eter, we measured the Wavefront distortions. As an example, we evaluated the Zernike coefficients giving the aberrations of spherical Wavefronts induced by a converging lens. Associated with a deformable mirror, the sensor will open the route to terahertz adaptive optics.
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Development of a Wavefront sensor for terahertz pulses
Optics Express, 2016Co-Authors: Emmanuel Abraham, Mathilde Brossard, Harsono Cahyadi, Jérôme Degert, Eric Freysz, Takeshi YasuiAbstract:Wavefront characterization of terahertz pulses is essential to optimize far-field intensity distribution of time-domain (imaging) spectrometers or increase the peak power of intense terahertz sources. In this paper, we report on the Wavefront measurement of terahertz pulses using a Hartmann sensor associated with a 2D electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. We quantitatively determined the deformations of planar and converging spherical Wavefronts using the modal Zernike reconstruction least-squares method. Associated with deformable mirrors, the sensor will also open the route to terahertz adaptive optics.
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Terahertz Wavefront assessment based on 2D electro-optic imaging
2015Co-Authors: H. Cahyadi, Takeshi Yasui, R. Ichikawa, J. Degert, E. Freysz, Emmanuel AbrahamAbstract:Complete characterization of terahertz (THz) radiation becomes an interesting yet challenging study for many years. In visible optical region, the Wavefront assessment has been proved as a powerful tool for the beam profiling and characterization, which consequently requires 2-dimension (2D) single-shot acquisition of the beam cross-section to provide the spatial profile in time- and frequency-domain. In THz region, the main problem is the lack of effective THz cameras to satisfy this need. In this communication, we propose a simple setup based on free-space collinear 2D electrooptic sampling in a ZnTe crystal for the characterization of THz Wavefronts. In principle, we map the optically converted, time-resolved data of the THz pulse by changing the time delay between the probe pulse and the generated THz pulse. The temporal waveforms from different lens-ZnTe distances can clearly indicate the evolution of THz beam as it is converged, focused, or diverged. From the Fourier transform of the temporal waveforms, we can obtain the spectral profile of a broadband THz wave, which in this case within the 0.1-2 THz range. The spectral profile also provides the frequency dependency of the THz pulse amplitude. The comparison between experimental and theoretical results at certain frequencies (here we choose 0.285 and 1.035 THz) is in a good agreement suggesting that our system is capable of THz Wavefront characterization. Furthermore, the implementation of Hartmann/Shack-Hartmann sensor principle enables the reconstruction of THz Wavefront. We demonstrate the reconstruction of THz Wavefronts which are changed from planar wave to spherical one due to the insertion of convex THz lens in the THz beam path. We apply and compare two different reconstruction methods: linear integration and Zernike polynomial. Roughly we conclude that the Zernike method provide smoother Wavefront shape that can be elaborated later into quantitative-qualitative analysis about the Wavefront distortion.
Emmanuel Abraham - One of the best experts on this subject based on the ideXlab platform.
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Interferometric Terahertz Wavefront Analysis
IEEE Journal of Selected Topics in Quantum Electronics, 2017Co-Authors: Emmanuel Abraham, Takayuki Ogawa, Mathilde Brossard, Takeshi YasuiAbstract:Wavefront characterization of terahertz beams is useful for various applications such as terahertz spectroscopy and imaging. In this paper, we report on the aberration measurement of a terahertz beam issued from a quantum cascade laser. By using a terahertz camera and a two-wave noncommon path interferom-eter, we measured the Wavefront distortions. As an example, we evaluated the Zernike coefficients giving the aberrations of spherical Wavefronts induced by a converging lens. Associated with a deformable mirror, the sensor will open the route to terahertz adaptive optics.
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Development of a Wavefront sensor for terahertz pulses
Optics Express, 2016Co-Authors: Emmanuel Abraham, Mathilde Brossard, Harsono Cahyadi, Jérôme Degert, Eric Freysz, Takeshi YasuiAbstract:Wavefront characterization of terahertz pulses is essential to optimize far-field intensity distribution of time-domain (imaging) spectrometers or increase the peak power of intense terahertz sources. In this paper, we report on the Wavefront measurement of terahertz pulses using a Hartmann sensor associated with a 2D electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. We quantitatively determined the deformations of planar and converging spherical Wavefronts using the modal Zernike reconstruction least-squares method. Associated with deformable mirrors, the sensor will also open the route to terahertz adaptive optics.
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Terahertz Wavefront assessment based on 2D electro-optic imaging
2015Co-Authors: H. Cahyadi, Takeshi Yasui, R. Ichikawa, J. Degert, E. Freysz, Emmanuel AbrahamAbstract:Complete characterization of terahertz (THz) radiation becomes an interesting yet challenging study for many years. In visible optical region, the Wavefront assessment has been proved as a powerful tool for the beam profiling and characterization, which consequently requires 2-dimension (2D) single-shot acquisition of the beam cross-section to provide the spatial profile in time- and frequency-domain. In THz region, the main problem is the lack of effective THz cameras to satisfy this need. In this communication, we propose a simple setup based on free-space collinear 2D electrooptic sampling in a ZnTe crystal for the characterization of THz Wavefronts. In principle, we map the optically converted, time-resolved data of the THz pulse by changing the time delay between the probe pulse and the generated THz pulse. The temporal waveforms from different lens-ZnTe distances can clearly indicate the evolution of THz beam as it is converged, focused, or diverged. From the Fourier transform of the temporal waveforms, we can obtain the spectral profile of a broadband THz wave, which in this case within the 0.1-2 THz range. The spectral profile also provides the frequency dependency of the THz pulse amplitude. The comparison between experimental and theoretical results at certain frequencies (here we choose 0.285 and 1.035 THz) is in a good agreement suggesting that our system is capable of THz Wavefront characterization. Furthermore, the implementation of Hartmann/Shack-Hartmann sensor principle enables the reconstruction of THz Wavefront. We demonstrate the reconstruction of THz Wavefronts which are changed from planar wave to spherical one due to the insertion of convex THz lens in the THz beam path. We apply and compare two different reconstruction methods: linear integration and Zernike polynomial. Roughly we conclude that the Zernike method provide smoother Wavefront shape that can be elaborated later into quantitative-qualitative analysis about the Wavefront distortion.
Jerry B. Griffiths - One of the best experts on this subject based on the ideXlab platform.
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Exact solutions for gravitational waves with cylindrical, spherical and toroidal Wavefronts
Classical and Quantum Gravity, 1996Co-Authors: G A Alekseev, Jerry B. GriffithsAbstract:Three families of exact vacuum solutions of Einstein's equations are presented which, when considered locally or in some finite spacetime region, describe gravitational waves with distinct nonplane Wavefronts propagating into a Minkowski background. The Wavefronts may be cylindrical, spherical or toroidal and may include impulsive or shock components or be characterized by arbitrarily weak discontinuities. Considered globally, without matching to any material sources but extending maximally as vacuum solutions, particular curvature singularities arise in the outer regions as the sources of these waves. Specifically, we find waves with a half-cylindrical Wavefront driven by two singular parallel half-planes moving apart at the speed of light, waves with a complete exact spherical Wavefront created by an expanding line singularity joining opposite poles of the Wavefront, and waves with toroidal fronts produced by two parallel coaxial disc-like singularities and an additional line singularity joining their centres. In each case, the character of the gravitational wave on the Wavefront is analysed and the collision and subsequent interaction of these waves is considered.
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Gravitational waves with spherical Wavefronts
Classical and Quantum Gravity, 1996Co-Authors: G A Alekseev, Jerry B. GriffithsAbstract:We present a large family of exact vacuum solutions of Einstein's equations which describe gravitational waves with a distinct spherical Wavefront and which propagate into a Minkowski background. The gravitational waves may have either shock Wavefronts or fronts on which the metric and the Weyl tensor components possess n continuous derivatives for any . The wave region behind the spherical Wavefront contains a line singularity.
Mathilde Brossard - One of the best experts on this subject based on the ideXlab platform.
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Interferometric Terahertz Wavefront Analysis
IEEE Journal of Selected Topics in Quantum Electronics, 2017Co-Authors: Emmanuel Abraham, Takayuki Ogawa, Mathilde Brossard, Takeshi YasuiAbstract:Wavefront characterization of terahertz beams is useful for various applications such as terahertz spectroscopy and imaging. In this paper, we report on the aberration measurement of a terahertz beam issued from a quantum cascade laser. By using a terahertz camera and a two-wave noncommon path interferom-eter, we measured the Wavefront distortions. As an example, we evaluated the Zernike coefficients giving the aberrations of spherical Wavefronts induced by a converging lens. Associated with a deformable mirror, the sensor will open the route to terahertz adaptive optics.
-
Development of a Wavefront sensor for terahertz pulses
Optics Express, 2016Co-Authors: Emmanuel Abraham, Mathilde Brossard, Harsono Cahyadi, Jérôme Degert, Eric Freysz, Takeshi YasuiAbstract:Wavefront characterization of terahertz pulses is essential to optimize far-field intensity distribution of time-domain (imaging) spectrometers or increase the peak power of intense terahertz sources. In this paper, we report on the Wavefront measurement of terahertz pulses using a Hartmann sensor associated with a 2D electro-optic imaging system composed of a ZnTe crystal and a CMOS camera. We quantitatively determined the deformations of planar and converging spherical Wavefronts using the modal Zernike reconstruction least-squares method. Associated with deformable mirrors, the sensor will also open the route to terahertz adaptive optics.
G A Alekseev - One of the best experts on this subject based on the ideXlab platform.
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Exact solutions for gravitational waves with cylindrical, spherical and toroidal Wavefronts
Classical and Quantum Gravity, 1996Co-Authors: G A Alekseev, Jerry B. GriffithsAbstract:Three families of exact vacuum solutions of Einstein's equations are presented which, when considered locally or in some finite spacetime region, describe gravitational waves with distinct nonplane Wavefronts propagating into a Minkowski background. The Wavefronts may be cylindrical, spherical or toroidal and may include impulsive or shock components or be characterized by arbitrarily weak discontinuities. Considered globally, without matching to any material sources but extending maximally as vacuum solutions, particular curvature singularities arise in the outer regions as the sources of these waves. Specifically, we find waves with a half-cylindrical Wavefront driven by two singular parallel half-planes moving apart at the speed of light, waves with a complete exact spherical Wavefront created by an expanding line singularity joining opposite poles of the Wavefront, and waves with toroidal fronts produced by two parallel coaxial disc-like singularities and an additional line singularity joining their centres. In each case, the character of the gravitational wave on the Wavefront is analysed and the collision and subsequent interaction of these waves is considered.
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Gravitational waves with spherical Wavefronts
Classical and Quantum Gravity, 1996Co-Authors: G A Alekseev, Jerry B. GriffithsAbstract:We present a large family of exact vacuum solutions of Einstein's equations which describe gravitational waves with a distinct spherical Wavefront and which propagate into a Minkowski background. The gravitational waves may have either shock Wavefronts or fronts on which the metric and the Weyl tensor components possess n continuous derivatives for any . The wave region behind the spherical Wavefront contains a line singularity.
