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Terahertz generation in quantum-cascade lasers through down-conversion optical nonlinearity: Design and modeling
摘要： In this paper, we propose an electrically driven optically excited laser structure for terahertz (THz) generation in quantum cascade lasers (QCLs) through frequency down-conversion optical nonlinearity. In our distinct design, both the pump and THz radiations are generated simultaneously by optical and electronic intersubband transitions (ISTs) between the quantized states within the conduction band of the same active region of a QCL. The modeling of laser bandstructure is achieved using a self-consistent solution of Schrodinger-Poisson equations, and the detailed analysis of electronic transport of the proposed structure is performed using the density matrix approach and energy-density balance equation that self-consistently consider the optical, electrical and thermal interactions in the structure. Additionally, the waveguide loss for the THz optical mode is considered using the bulk Drude model. Using a stationary solution of the density matrix equations, an expression for the THz intensity gain is derived as a function of pump field intensity, carrier distributions and quantum coherence contributions. Using the presented model, we analyze the steady-state and transient characteristics of the device for two different heatsink temperatures, 220 and 300 K. Simulation results show that the proposed structure has a potential to generate room-temperature THz radiation in QCLs.
关键词： Quantum-cascade laser (QCL),terahertz (THz) generation,down-conversion optical nonlinearity,density-matrix formalism
更新于2025-09-23 15:21:01
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Effects of a chiral atomic medium on the manipulation of light birefringence and lateral Goos–H?nchen shifts via Kerr nonlinearity and local field effects
摘要： We present a new scheme to report on the effects of a five-level chiral atomic medium on the lateral Goos–H?nchen (GH) shift in Gaussian probe beams via Kerr nonlinearity (KNL) and local field effects. The physical realization of birefringence in absorption, dispersion, reflection and transmission beams is investigated, with special emphasis on the manipulation of absolute and fractional change in lateral GH shifts in birefringence transmission and reflection beams, via local fields and Kerr nonlinearity. We have employed a semiclassical atomic density-matrix formalism so as to obtain the expression for electric and magnetic susceptibilities of the chiral medium and the corresponding chirality coefficients in conjunction with Kerr and local fields, both separately and in combination. Stationary-phase theory is used to compute GH shift from the calculated birefringent reflection and transmission coefficients of probe beams. A negative and positive GH shift is observed in reflection and transmission beams, respectively, subjected to local field and Kerr effect. In contrast, a positive GH shift is observed in both reflection and transmission beams in the presence of both local field and Kerr effects. The local and Kerr fields also alter the divergence angle between left and right circularly polarized birefringence beams. GH shift depends on incident angle and probe detuning. The anisotropy of medium is lessened by switching ON the Kerr field in the medium. We observed a positive fractional change of ±30% in the GH shift in the birefringence reflection beam in the presence of a local field without KNL, while a 20% fractional GH shift was observed in the presence of both local field and KNL effects. Our results suggest promising applications in nonlinear optical, plasmonic and biophotonic devices for the manipulation of light propagation and optical signal processing.
关键词： stationary-phase theory,Kerr nonlinearity,birefringence chiral medium,Goos–H?nchen shift,density-matrix formalism,Doppler broadening medium
更新于2025-09-23 15:19:57
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Implications of spectral-hole burning on the manipulation of spatial Goos–H?nchen shift in an atomic cell
摘要： We present a new scheme to report on Goos–H?nchen (GH) shift experienced by the Gaussian light beam incident at the plane optical interface filled with four-level sodium atomic medium in the spectral-hole burning region with and without Doppler broadening effect. Theoretical atomic density-matrix formalism is employed to obtain the susceptibility of atomic medium while the stationary-phase-theory is used to compute the GH shift in the reflected and transmitted probe beams subjected to control fields. A steep normal slope of dispersion is observed with a maximum and zero probability of transmission and reflection coefficients, respectively, at the regions of the spectral holes burning. In the normal dispersion spectrum at the region of spectral-hole burning, positive and negative GH shift is observed, respectively, in the transmitted and reflected light beams. However, at anomalous dispersive regions negative GH shift in the transmission beam and positive GH shift in the reflection beam is observed. The reflection and transmission coefficients as well as the spatial GH shift are the functions of probe detuning, collective phase of control fields and inverse Doppler broadening effect in the spectral-hole burning region. The study is expected to be useful for optoelectronic devices and optical-clocking applications.
关键词： Doppler broadening medium,Density-matrix formalism,Spectral hole burning,Spatial Goos–H?nchen shift,Stationary-phase-theory
更新于2025-09-09 09:28:46