- 标题
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Effect of dual-channel optical feedback on self-mixing interferometry system
摘要： Laser feedback interference is widely used for displacement measurement of non-cooperative targets due to its ultra-high sensitivity. However, by the same token, laser feedback interferometry (LFI) suffers from multi-channel optical feedback, which compromises measurement stability and accuracy. We perform both simulations and experiments to study the effect of dual-channel optical feedback on LFI systems based displacement measurement. Dual-channel optical feedback interference is the simplest and most representative form of multi-channel feedback interference. We evaluate system performance by varying ,a which is the ratio of feedback level in the primary channel to the one in the secondary channel. The results indicate that the measured displacement curve is a linear line superimposed with nonlinear periodic errors when the target in the primary channel moves linearly and the target in the secondary channel stays stationary. Whereas, the curve is a periodic curve instead of a linear one, for the case when the target in the secondary channel moves linearly while the one in the primary channel stays stationary. Furthermore, the amplitude and shape of the periodic curves also depend on the parameter .a When a is much less than 1, the displacement curve is sinusoidal, whereas the curve has a saw-tooth shape with larger amplitude for a close to 1. In view of this situation, a new displacement measurement method, counting the cycles of the periodic displacement curves, is proposed. The current work can provide theoretical and experimental suggestions for improving the performance of existing self-mixing interferometry systems, and implementing ones with multi-channel optical feedback channels.
关键词： rate equations,interferometry,self-mixing,laser feedback
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Zatoka, Ukraine (2018.9.9-2018.9.14)] 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Time-Resolved Photoluminescence of CdSe/CdS/CdZnS Quantum Dots
摘要： We demonstrate that in the study of time-resolved photoluminescence the signatures of biexcitons in QDs can manifest themselves even when the system is excited by long laser pulses with their duration of the order of several tens of picoseconds. To describe the results of our measurements we propose an elegant theoretical model. It is based on the introduction of auxiliary sources in the rate equations. The parameters of the sources are determined by fitting the analytical solution of these equations that describes the full emission of the system to the experimental results obtained. Having found the parameters of the auxiliary sources we can determine the temporal dependences of the radiation from excitons and biexcitons separately. We find the spectral positions of the exciton and biexciton emission bands, their widths, and the biexciton binding energy.
关键词： quantum dots,photoluminescence,exciton,rate equations,binding energy,biexciton
更新于2025-09-23 15:19:57
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Passively Q-switched near-infrared lasers with bismuthene quantum dots as the saturable absorber
摘要： Bismuthene quantum dots (Bi-QDs) were synthesized via the liquid phase exfoliation (LPE) method for the passive Q-switching operation in near-infrared (NIR) region. The nonlinear optical properties of the prepared Bi-QDs were investigated by the open-aperture Z-scan technology. The modulation depths were 18.1% and 5.1% at 1.06 and 1.34 μm, respectively. Based on the Bi-QDs saturable absorber, passively Q-switched Nd:GdVO4 lasers operating at 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2 transitions were demonstrated, showing the wideband optical modulation in NIR regime. For the 4F3/2 → 2I13/2 transition lasing at 1.34 μm, the shortest pulse duration of 155 ns was obtained with a repetition rate of 457 kHz. With respect to the 4F3/2 → 2I11/2 transition at 1.06 μm, the minimum pulse duration was 150 ns with a repetition rate of 424 kHz, leading to a single pulse energy of 261 nJ and a peak power of 1.68 W. In addition, the ground state absorption cross section and the excited state absorption cross section of Bi-QDs were also investigated for the ?rst time. The impact of the excited state lifetime on the output parameters was numerically stimulated by the coupled rate equations. Our work con-?rmed that the trap state in Bi-QDs played an important role in the pulse generation mechanism.
关键词： Saturable absorber,Bismuthene quantum dots,Q-switching,Nonlinear Optical properties,Rate equations
更新于2025-09-23 15:19:57
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Local and mean-???eld approaches for modeling semiconductor spin-lasers
摘要： Electrically and optically pumped spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) seem to reach improved performance compared to their conventional counterparts. Their dynamical properties are studied mostly in the framework of e?ective rate equations containing parameters that are di?cult to directly relate with fundamental material properties. Consequently, such approaches are not suitable for the precise design and optimization of future spin-lasers with desirable dynamical properties. We propose a method for extraction of dynamics-related parameters for spin-?ip model (SFM), that is used widely for the description of spin-laser dynamics. This method is based on the correspondence between robust local computational tools and e?ective models. General matrix formalism based on S-matrices and generalized Maxwell-Bloch equations is used to determine approximate values of parameters such as cavity decay rate or birefringence rate. This would allow to tune laser properties by changing optical properties of laser cavities and active media according to our needs. The method is demonstrated on realistic anisotropic spin-VCSEL structures containing 12-quantum well (QW) limitations of already existing InGaAs/GaAsP active region. The potential e?ective models are discussed.
关键词： anisotropies,scattering matrix formalism,rate equations,spin-laser,VCSEL
更新于2025-09-19 17:13:59
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Rate for laser-induced nuclear dipole absorption
摘要： Using the Brink-Axel hypothesis we derive the rate R for nuclear dipole excitation by a laser pulse carrying N (cid:2) 1 photons with average energy ˉhω0 ≈ 5 MeV. As expected R ∝ ( ˉhω0)3. The rate is also proportional to the aperture α of the laser pulse. Perhaps less expected is the fact that R ∝ N, irrespective of the degree of coherence of the laser pulse. The expression for R, derived for a nearly stationary laser pulse, is valid also for short times and can, thus, be used in simulations via rate equations of multiple nuclear dipole excitations by a single pulse. The explicit dependence of R on the parameters of the laser pulse and on nuclear parameters given in the paper should help to optimize experiments on laser-nucleus reactions.
关键词： laser pulse,Giant Dipole Resonance,nuclear dipole excitation,Brink-Axel hypothesis,rate equations
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 4th Optoelectronics Global Conference (OGC) - Shenzhen, China (2019.9.3-2019.9.6)] 2019 IEEE 4th Optoelectronics Global Conference (OGC) - Theoretical Evaluation of a Pulsed Mid-Infrared Ho <sup>3+</sup> :BaY <sub/>2</sub> F <sub/>8</sub> Laser
摘要： In this study, we construct a theoretical model to analyze the output characteristics of a pulsed Ho3+:BaY2F8 (Ho3+:BYF) laser by taking both energy transfer up-conversion (ETU) and cross relaxation (CR) processes into account. The influences of the pump energy, pulse width, reflectance of an output coupler (OC), crystal length, and Ho3+ doping concentration on the physical performances are investigated in detail for an end-pumped structure. The calculation results reveal that the proper length of a Ho3+:BaY2F8 crystal is from 5 to 10 mm for the Ho3+ doping concentration of 10-40 at.%. We also deduce that a high output can be obtained when the Ho3+ doping concentration is selected as 30 at.%. It has been demonstrated that the relaxation oscillation of a Ho:BYF laser can be observed for a pulsed pump source. We can see that the threshold peak power of a pump light source decreases with the increase of the pulse width. The conclusions might be useful for the realization of a pulsed mid-infrared Ho3+:BYF laser.
关键词： rate equations,mid-infrared laser,directly-pumped,Ho3+:BaY2F8
更新于2025-09-16 10:30:52
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Rate equations for the diode laser and their applicability area
摘要： Taking into account spontaneous emission by adding its intensity in the form of a constant term to the laser emission intensity in rate equations is shown to be an inadequate approach. The use of rate equations without equations for phases of waves is limited to problems in which light is characterised by its total intensity, without its spectral composition. Such equations are incapable of adequately modelling the emission spectrum of diode lasers.
关键词： diode lasers,spontaneous emission,rate equations
更新于2025-09-12 10:27:22
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Influence of integrated optical Feedback on tunable Lasers
摘要： In this paper we explain how to use rate equations to describe a laser that includes integrated optical feedback. We find a relation between the threshold current, the voltage drop at the gain section, output power, linewidth, and side mode suppression ratio, and show experimental results.
关键词： Frequency Stabilization,Continuous Tuning,Gain Voltage,Wavelength Stabilization,Optical Feedback Interferometry,Tunable Laser,Output Power,Rate Equations,Laser Stability,Linewidth,Optical Feedback,Side Mode Suppression Ratio,Wavelength locking
更新于2025-09-12 10:27:22
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Laser refrigeration of gas filled hollow-core fibres
摘要： We evaluate prospects, performance and temperature limits of a new approach to macroscopic scale laser refrigeration. The considered refrigeration device is based on exciplex-mediated frequency up-conversion inside hollow-core fibers pressurized with a dopant - buffer gas mixture. Exciplexes are excited molecular states formed by two atoms (dopant and buffer) which do not form a molecule in the ground state but exhibit bound states for electronically excited states. The cooling cycle consists of absorption of laser photons during atomic collisions inducing light assisted exciplex formation followed by blue-shifted spontaneous emission on the atomic line of the bare dopant atoms after molecular separation. This process, closely related to reversing the gain mechanism in excimer lasers, allows for a large fraction of collision energy to be extracted in each cycle. The hollow-core fiber plays a crucial role as it allows for strong light-matter interactions over a long distance, which maximizes the cooling rate per unit volume and the cooling efficiency per injected photon while limiting re-absorption of spontaneously emitted photons channeled into unguided radiation modes. Using quantum optical rate equations and refined dynamical simulations we derive general conditions for efficient cooling of both the gas and subsequently of the surrounding solid state environment. Our analytical approach is applicable to any specific exciplex system considered and reveals the shape of the exciplex potential landscapes as well as the density of the dopant as crucial tuning knobs. The derived scaling laws allow for the identification of optimal exciplex characteristics that help to choose suitable gas mixtures that maximize the refrigeration efficiency for specific applications.
关键词： quantum optical rate equations,exciplex-mediated frequency up-conversion,laser refrigeration,hollow-core fibers,cooling efficiency
更新于2025-09-12 10:27:22
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Numerical and Experimental Analysis of Optical Frequency Comb Generation in Gain-Switched Semiconductor Lasers
摘要： We have performed a systematic experimental and simulation analysis of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The simulations have been produced with a dynamical model consisting of three rate equations that include stochastic noise terms. The model parameters have been extracted from experiments. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra generated under a wide range of switching and optical injection conditions has been performed. The excellent quantitative agreement found in the entire range of the explored operating conditions supports the validity of the model for the analysis of the comb generation mechanisms. The detailed maps generated provide guidelines for selecting suitable operating conditions for specific comb characteristics.
关键词： optical frequency combs,Semiconductor lasers,rate equations,optical injection,gain switching
更新于2025-09-11 14:15:04