The Experts below are selected from a list of 42837 Experts worldwide ranked by ideXlab platform
Roman Sobolewski - One of the best experts on this subject based on the ideXlab platform.
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femtosecond optical generation and detection of coherent acoustic phonons in gan single crystals
Physical Review B, 2007Co-Authors: P Geiser, J Jun, J Karpinski, Roman SobolewskiAbstract:We report our experimental and theoretical studies on the time-resolved generation and detection of coherent acoustic phonons (CAPs) in very high quality bulk GaN single crystals, performed using a femtosecond, two-color, all-optical pump-Probe technique. A train of ultraviolet laser pulses with energy above the GaN energy gap induced the transient electronic stress at the GaN surface, responsible for the CAP generation. Subsequent CAP oscillations, propagating without any measurable intrinsic attenuation, were observed by scanning the transient differential reflectivity signal $(\ensuremath{\Delta}R∕R)$ of the near-infrared, far-below-band-gap Probe Beam. The $\ensuremath{\Delta}R∕R$ CAP oscillation amplitude was of the order of ${10}^{\ensuremath{-}5}--{10}^{\ensuremath{-}6}$ and was dependent only on the pump-photon absorption coefficient spectral characteristics. The CAP oscillation frequency was dispersionless (proportional to the Probe-Beam wave vector) with the slope corresponding to $8002\ifmmode\pm\else\textpm\fi{}22\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$---the speed of sound in GaN---while the CAP signal phase was constant within the entire range of our experiments. The above experimental results are in excellent agreement with our theoretical modeling and the published literature data.
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long lived coherent acoustic phonon oscillations in gan single crystals
Applied Physics Letters, 2006Co-Authors: P Geiser, J Jun, J Karpinski, Jungrae Park, Roman SobolewskiAbstract:We report on coherent acoustic phonon (CAP) oscillations studied in high-quality bulk GaN single crystals with a two-color femtosecond optical pump-Probe technique. Using a far-above-the-band gap ultraviolet excitation (∼270nm wavelength) and a near-infrared Probe Beam (∼810nm wavelength), the long-lived, CAP transients were observed within a 10 ns time-delay window between the pump and Probe pulses, with a dispersionless (proportional to the Probe-Beam wave vector) frequency of ∼45GHz. The measured CAP attenuation corresponded directly to the absorption of the Probe light in bulk GaN, indicating that the actual (intrinsic) phonon-wave attenuation in our crystals was significantly smaller than the measured 65.8cm−1 value. The velocity of the phonon propagation was equal to the velocity of sound in GaN.
Edward William James Hyland - One of the best experts on this subject based on the ideXlab platform.
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phase cycling schemes for pump Probe Beam geometry two dimensional electronic spectroscopy
Chemical Physics Letters, 2012Co-Authors: Zhengyang Zhang, Kym Lewis Wells, Edward William James HylandAbstract:Experimental demonstrations and detailed theoretical explanations are provided for a thorough understanding of the various phase-cycling schemes in an optical pulse shaper assisted two-dimensional electronic spectroscopy (2DES) in a pump–Probe Beam geometry. We show that two and three-step phase-cycling schemes can be employed to retrieve both rephasing and nonrephasing 2D spectra. The studies were performed on the Qy transition of chlorophyll a.
Ninghua Zhu - One of the best experts on this subject based on the ideXlab platform.
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photonics generation of frequency shift keying radio frequency signal using nonlinear polarization rotation in a highly nonlinear fiber
Optical Engineering, 2016Co-Authors: Xin Wang, Ninghua ZhuAbstract:We experimentally demonstrate an all-optical approach for generating frequency-shift keying (FSK) radio-frequency (RF) signal based on nonlinear polarization rotation (NPR) in a highly nonlinear fiber (HNLF). A continuous wave Probe Beam is polarization-rotated by an optical amplitude-shift keying control Beam via NPR in the HNLF. After removing the undesired control Beam by a tunable optical filter, the polarization-rotated Probe Beam is converted to an intensity-modulated optical signal using a polarizer. By carefully adjusting the polarization controller before the polarizer and the optical power of the control Beam, FSK RF signals are generated after photodetection.
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photonic generation of triangular pulses based on nonlinear polarization rotation in a highly nonlinear fiber
Optics Letters, 2014Co-Authors: Wei Yu Wang, Wen Hui Sun, Wen Ting Wang, Jianguo Liu, Ninghua ZhuAbstract:We propose a novel method to generate triangular pulses based on the nonlinear polarization rotation (NPR) effect in a highly nonlinear fiber. A continuous wave Probe Beam is polarization-rotated by an intensity-modulated control Beam via the NPR effect. A polarization-division-multiplexing emulator is exploited to split the Probe Beam into two orthogonally polarized states with imbalanced time delay. After detection by a photodetector, a 90° microwave phase shifter is used to compensate the phases of the fundamental and the third-order harmonic components in order to generate triangular pulses. Triangular pulses at 5 and 6 GHz with full duty cycles are experimentally generated. The root mean square errors between the generated and the simulated waveforms are 3.6e-4 and 1e-4 for triangular pulses at 5 and 6 GHz, respectively.
P Geiser - One of the best experts on this subject based on the ideXlab platform.
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femtosecond optical generation and detection of coherent acoustic phonons in gan single crystals
Physical Review B, 2007Co-Authors: P Geiser, J Jun, J Karpinski, Roman SobolewskiAbstract:We report our experimental and theoretical studies on the time-resolved generation and detection of coherent acoustic phonons (CAPs) in very high quality bulk GaN single crystals, performed using a femtosecond, two-color, all-optical pump-Probe technique. A train of ultraviolet laser pulses with energy above the GaN energy gap induced the transient electronic stress at the GaN surface, responsible for the CAP generation. Subsequent CAP oscillations, propagating without any measurable intrinsic attenuation, were observed by scanning the transient differential reflectivity signal $(\ensuremath{\Delta}R∕R)$ of the near-infrared, far-below-band-gap Probe Beam. The $\ensuremath{\Delta}R∕R$ CAP oscillation amplitude was of the order of ${10}^{\ensuremath{-}5}--{10}^{\ensuremath{-}6}$ and was dependent only on the pump-photon absorption coefficient spectral characteristics. The CAP oscillation frequency was dispersionless (proportional to the Probe-Beam wave vector) with the slope corresponding to $8002\ifmmode\pm\else\textpm\fi{}22\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$---the speed of sound in GaN---while the CAP signal phase was constant within the entire range of our experiments. The above experimental results are in excellent agreement with our theoretical modeling and the published literature data.
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long lived coherent acoustic phonon oscillations in gan single crystals
Applied Physics Letters, 2006Co-Authors: P Geiser, J Jun, J Karpinski, Jungrae Park, Roman SobolewskiAbstract:We report on coherent acoustic phonon (CAP) oscillations studied in high-quality bulk GaN single crystals with a two-color femtosecond optical pump-Probe technique. Using a far-above-the-band gap ultraviolet excitation (∼270nm wavelength) and a near-infrared Probe Beam (∼810nm wavelength), the long-lived, CAP transients were observed within a 10 ns time-delay window between the pump and Probe pulses, with a dispersionless (proportional to the Probe-Beam wave vector) frequency of ∼45GHz. The measured CAP attenuation corresponded directly to the absorption of the Probe light in bulk GaN, indicating that the actual (intrinsic) phonon-wave attenuation in our crystals was significantly smaller than the measured 65.8cm−1 value. The velocity of the phonon propagation was equal to the velocity of sound in GaN.
X.-c. Zhang - One of the best experts on this subject based on the ideXlab platform.
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spatial sampling of terahertz fields with sub wavelength accuracy via Probe Beam encoding
Light-Science & Applications, 2019Co-Authors: Jiapeng Zhao, X.-c. Zhang, E Yiwen, Kaia Williams, Robert W BoydAbstract:Recently, computational sampling methods have been implemented to spatially characterize terahertz (THz) fields. Previous methods usually rely on either specialized THz devices such as THz spatial light modulators or complicated systems requiring assistance from photon-excited free carriers with high-speed synchronization among multiple optical Beams. Here, by spatially encoding an 800-nm near-infrared (NIR) Probe Beam through the use of an optical SLM, we demonstrate a simple sampling approach that can Probe THz fields with a single-pixel camera. This design does not require any dedicated THz devices, semiconductors or nanofilms to modulate THz fields. Using computational algorithms, we successfully measure 128 × 128 field distributions with a 62-μm transverse spatial resolution, which is 15 times smaller than the central wavelength of the THz signal (940 μm). Benefitting from the non-invasive nature of THz radiation and sub-wavelength resolution of our system, this simple approach can be used in applications such as biomedical sensing, inspection of flaws in industrial products, and so on. A convenient and practical scheme for spatially characterizing terahertz (THz) signals has been invented by scientists in the US. The approach could prove useful for applications such as Beam profiling, biomedical sensing, flaw detection and security screening. Jiapeng Zhao and coworkers from the University of Rochester make use of the electrooptic effect in a ZnTe crystal to indirectly measure the spatial profile of a THz signal with a resolution of λ/15 (62 microns), 128 × 128 sample points and kilohertz sampling speed. The approach relies on the fact that when a THz signal interacts with the ZnTe crystal it induces birefringence, which modifies the polarization of a near-infrared (NIR) Probe Beam. Spatially-modulating the NIR Probe and measuring its polarization rotation via a single-pixel detector thus makes it possible to determine the profile of the THz Beam.
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spatial sampling of terahertz fields with sub wavelength accuracy via Probe Beam encoding
arXiv: Optics, 2019Co-Authors: Jiapeng Zhao, X.-c. Zhang, E Yiwen, Kaia Williams, Robert W BoydAbstract:Recently, computational sampling methods have been implemented to spatially characterize terahertz (THz) fields. Previous methods usually rely on either specialized THz devices such as THz spatial light modulators, or complicated systems requiring assistance from photon-excited free-carriers with high-speed synchronization among multiple optical Beams. Here, by spatially encoding an 800 nm near-infrared (NIR) Probe Beam through the use of an optical SLM, we demonstrate a simple sampling approach that can Probe THz fields with a single-pixel camera. This design does not require any dedicated THz devices, semiconductors or nanofilms to modulate THz fields. Through the use of computational algorithms, we successfully measure 128$\times$128 field distributions with a 62 $\mu m$ transverse spatial resolution, more than 15 times smaller than the central wavelength of the THz signal (940 $\mu m$). Benefitting from the non-invasive nature of THz radiation and sub-wavelength resolution of our system, this simple approach can be used in applications such as biomedical sensing, inspection of flaws. in industrial products, and so on.
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analysis of terahertz pulse measurement with a chirped Probe Beam
Applied Physics Letters, 1998Co-Authors: Zhiping Jiang, X.-c. ZhangAbstract:In this letter, terahertz (THz) pulse measurements with a chirped Probe pulse are analyzed. The method of stationary phase is used to explore the relation between the temporal waveform of an input THz pulse and spectral distribution of an output Probe pulse on a detector array. The dependence of the temporal resolution on the chirp rate, the spectrum of the chirped Probe Beam, and the spectral resolution of the spectrometer is discussed. We confirm that the temporal resolution of the chirped pulse technique is equal to the square root of the product of the original unchirped Probe pulse duration and the chirped pulse duration.
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electro optic measurement of thz field pulses with a chirped optical Beam
Applied Physics Letters, 1998Co-Authors: Zhiping Jiang, X.-c. ZhangAbstract:Using a linearly chirped optical Probe pulse in free-space electro-optic measurements, a temporal wave form of a co-propagating THz field is linearly encoded onto the frequency spectrum of the optical Probe pulse, and then decoded by dispersing the Probe Beam from a grating to a detector array. We achieve acquisition of picosecond THz field pulses without using mechanical time-delay device. We also demonstrate a single-shot electro-optic measurement of the temporal wave form of a THz pulse.
