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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Superradiance as a Way to the Steady-State Multimode and Ultrashort Pulsed Lasing in CW Quantum-Dot Heterolasers
摘要： On the basis of the Maxwell-Bloch equations, we demonstrate theoretically and numerically that the pulsed superradiant lasing is possible in the quantum-dot heterostructures under continuous-wave (CW) optical pumping if the quantum-dot coherence lifetime exceeds the photon lifetime in a laser cavity [1, 2]. We analyze/compare in detail and select the most promising multilayered well-dot and sub-monolayer quantum-dot heterostructures which could be used as the active media, and design for them the proper low-Q combined Fabry-Perot cavities with distributed feedback which will select the superradiant modes. We investigate various operational regimes of the superradiant lasing and the intriguing quantum-coherent features of both cooperative and individual dynamics of quantum dots under the action of a self-consistent intracavity field preserving the long-term and wide-spectral coherence. Among the remarkably diverse operational regimes of the laser, we find the quasi-stationary, self-modulated, regular or irregular pulsed, self-locked, and stochastic regimes. In particular, we show that one or several superadiant modes may emit the quasiperiodic sequences of ultrashort subpicosecond pulses with comparable periods of the order of picoseconds and at the same time give rise to many steady-state modes with quasi-equidistant spectrum (see a fig. 1). The letter used to be self-locked due to the superradiant coherent dynamics of quantum dots, so that an additional sequence of ultrashort subpicosecond pulses with a round-trip period are emitted in the absence of any active or passive mode-locking elements. We indicate the ways how (i) to overcome an additional relaxation of the quantum-dot coherence in the presence of incoherent pumping and suppression of the superradiant gain within an inhomogeneously broadened spectral line of quantum dots continuously, i.e., during the entire time of laser operation, and (ii) to ensure a fully cycling pump-emission scheme of the quantum dots’ dynamics including a fast depletion of the lower-energy states under a CW pumping of the upper-energy states and to minimize extra heating which accompanies this cycling process and increases the relaxation of coherence. The suggested pulsed multimode superradiant heterolaser will offer a number of applications in the information optics, data processing, fiber network systems, wideband dynamic spectroscopy and diagnostics of various materials since it will be the first compact source of coherent radiation with a wide variety of controllable quantum-correlation and spectral-temporal properties. Also, such a heterolaser is a unique object for the studies of complex coherent processes in the semiconductor heterostructures.
关键词： Continuous-Wave Optical Pumping,Ultrashort Pulsed Lasing,Quantum-Dot Heterolasers,Maxwell-Bloch Equations,Superradiance
更新于2025-09-12 10:27:22
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Enhanced Pump Absorption Efficiency in Coiled and Twisted Double-Clad Fibers for Fiber Lasers
摘要： High-power operation of fiber lasers was mainly enabled by the invention of cladding-pumping in a double-clad fiber structure. Pump absorption is enhanced by broken circular symmetry of inner cladding cross-sections and by mode-scrambling of the pump modes resulting from unconventional fiber coiling. However, theoretical studies were limited to the assumption of a straight fiber until recently, when the rigorous model accounting for double-clad fiber bending and twisting was described. It was found that squeezing of the effective area of the pump radiation due to fiber bending plays an important role in cladding-pump absorption enhancement. We review results of numerical modeling of pump absorption in various types of double-clad fibers, e.g., with cross-section shape of hexagon, stadium, and circle; two-fiber bundle (so-called GTWave fiber structure) a panda fibers are also analyzed. The presented results can have a practical application and potential impact in the construction of fiber lasers: with pump absorption efficiency optimized by our new model (the other models did not take into account fiber twist), the double-clad fiber of shorter length can be used in the fiber lasers and amplifiers. This dramatically minimizes the deleterious effect of background losses and nonlinear effects.
关键词： fiber lasers,thulium-doped fibers,rare-earth-doped fibers,optical pumping
更新于2025-09-11 14:15:04
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Production of Hyperpolarized 129Xe Using Spin Exchange Optical Pumping
摘要： We present a constructed setup for polarizing 129Xe noble gas. Hyperpolarized 129Xe has been obtained via spin exchange with an optically pumped rubidium vapor. Optical pumping is based on polarizing the valence electron of rubidium by the resonant absorption of a circularly polarized laser light. The magnetic ?eld of 30 G was used for obtaining 129Xe polarization. The apparatus for detecting polarization is a nuclear magnetic resonance spectrometer. The highest 129Xe polarization of 54% has been obtained using 60 W circularly polarized laser light with wavelength of 794.7 nm. The measured longitudinal relaxation time of the hyperpolarized 129Xe was 72.3 minutes.
关键词： Nuclear magnetic resonance,Polarized 129Xe,Spin exchange,Polarization,Optical pumping,Rubidium
更新于2025-09-09 09:28:46
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[Advances In Atomic, Molecular, and Optical Physics] Volume 67 || Radio-Frequency Spectroscopy as a Tool for Studying Coherent Spin Dynamics and for Application to Radio-Frequency Magnetometry
摘要： The technique of radio-frequency spectroscopy was introduced more than 50 years ago, but is continuing to evolve and is being used as an ever-more versatile tool. We describe the underlying processes that govern the various contributions to the spectroscopic signals, considering the atom-light couplings. We then apply this understanding to demonstrate how the coherent dynamics can be manipulated with different configurations of optical pumping. Finally, we discuss how to implement rf spectroscopy to give optimized sensitivity in atomic magnetometers.
关键词： radio-frequency spectroscopy,atom-light couplings,atomic magnetometry,optical pumping,coherent spin dynamics
更新于2025-09-04 15:30:14