Negative Detuning Research Articles

Polaron Photoconductivity in the Weak and Strong Light-Matter Coupling Regime.

We investigate the potential for cavity-modified electron transfer in a doped organic semiconductor through the photocurrent that arises from exciting charged molecules (polarons). When the polaron optical transition is strongly coupled to a Fabry-Perot microcavity mode, we observe polaron polaritons in the photoconductivity action spectrum and find that their magnitude depends differently on applied electric field than photocurrent originating from the excitation of uncoupled polarons in the same cavity. Crucially, moving from positive to negative detuning causes the upper and lower polariton photocurrents to swap their field dependence, with the more polaronlike branch resembling that of an uncoupled excitation. These observations are understood on the basis of a phenomenological model in which strong coupling alters the Onsager dissociation of polarons from their dopant counterions by effectively increasing the thermalization length of the photoexcited charge carrier.

Nonclassicality of the two-photon laser with Kerr nonlinearity

We have studied the photon statistics of the non-degenerate two-photon laser composed of many noninteracting atoms with Kerr nonlinearity. Nonlinearity of the gain is accounted for by the Lamb–Scully approach. Under certain conditions, we obtain an approximate photon distribution function. In the region above lasing threshold, the first few moments of the photon numbers are calculated analytically, and the threshold condition for stable lasing that depends on the Kerr parameter and detuning are obtained. We analyze the properties of the cavity field through the Mandel Q parameter, second-order correlation functions, Cauchy–Schwarz inequality for a range of Kerr parameters, atomic injection rate, and cavity detuning. Nonclassicality of the field is found through sub-Poissonian statistics, particularly at a low injection rate and high Kerr coupling with negative detuning. These nonclassicality conditions correspond to low photon numbers and depend on the sign of the detuning. The violation of the Cauchy–Schwarz inequality also occurs at low photon numbers but over a wide range of parameters, especially at short transient times. Our results show that the two-photon laser with Kerr nonlinearity is a promising quantum nonlinear optical system for developing controllable nonclassical light sources.

Two-color flat-top solitonic pulses in χ(2) optical microresonators via second-harmonic generation

We studied numerically the generation of the coherent frequency combs at second harmonic generation in $\chi^{(2)}$ microresonators via conventional frequency scan method. It was demonstrated for the first time that under particular conditions it is possible to generate two-color flat-top solitonic pulses, platicons, using pump amplitude modulation or controllable mode interaction approach, if the signs of the group velocity coefficients at pump frequency and its second harmonic are opposite but absolute values of these coefficients are rather close. It was revealed that platicons may be observed on both sides of the linear microresonator resonance (at positive, as well as negative pump frequency detunings). For the efficient platicon excitation, one needs simultaneous accurate matching of both microresonator free spectral ranges and resonant eigenfrequencies. Platicon generation processes were simulated numerically, excitation conditions and platicon generation domains were found for different generation methods, and the properties of generated platicons were studied for the different combinations of the medium parameters.

Theoretical Performance Evaluation of Optical Complex Signals Based on Optically Injection-Locked Semiconductor Lasers

We developed a method to generate optical complex signals based on optically injection-locked (OIL) semiconductor lasers and numerically evaluated their performance depending on the injection-locking parameters, injection ratio, and detuning frequency. We first determined the stable/unstable locking regions of the OIL system as a function of the injection-locking parameters through steady-state analysis. We then mapped the optical complex signal in both the stable injection-locking region and the complex signal plane. Based on the mapped relationship between the positions in the conventional injection-locking map and the complex signal plane, we theoretically evaluated the optical trajectories and constellation diagrams for the optical phase-shift keying signals and calculated the error-vector-magnitude with a data rate of 10 Gbaud/s using a time-domain calculation. We found that the complex signal performance could be improved using a higher injection ratio under a large negative detuning frequency.

Optimal Reduction of the Vibration of the Flexible-Shaft-Disk-Blades System Using a Set of Nonlinear Energy Sinks on the Disk

Recently, modern turbines are designed close to their critical operating points with lower stability margin. Therefore, accurate dynamic analysis and using advanced vibration control systems are required. In this paper, the application of nonlinear energy sinks (NESs) for indirect vibration reduction of the blades in a flexible shaft-disk-blades system of a real steam turbine is conducted. 37 packets of seven-connected blades are mounted on the perimeter of the disk. The cyclic finite element analysis is employed to obtain mode shapes and frequency diagram. For the second combined mode of system, which is a combination of the second bending mode of shaft and the third bending mode of disk-blades, a two degrees of freedom (2DOFs) reduced order model (ROM) is identified for each sector. The cyclic symmetry of ROM reduces the size of the studied model to 2 DOFs. NESs with a small mass, an essential nonlinear stiffness and a linear damping are installed on the ROM in the antinode position of desired mode. The Runge-Kutta method is used to solve the nonlinear equations numerically. Optimum stiffness and damping of the NESs are determined to minimize the vibration amplitude of the blades.The results show the occurrence of strongly modulated response around the resonance, and hence, the desired vibration reduction of the blades is take placed. If the NESs have large nonlinear stiffness or low damping, a saddle-node bifurcation and a large island form near the resonance, and the blades could experience large amplitude periodic motion in the negative detuning frequencies.

Deposition of Cr Atoms Using Switching-Detuning Light Mask for Direct Atom Lithography

Background: As progress on the nanofabrication has made semiconductor developed rapidly, there is an increasing need in precise pitch standards to calibrate the structure of devices at nanoscale. Nano-gratings fabricated by atom lithography are unique and suitable to act as precise pitch standard because its pitch distance is directly traceable to a natural constant. As the scaling down of nano-devices, it is very challenging to double the spatial frequency of nano-grating while keeping the self-traceability in atom lithography. Methods: In this study, the switching-detuning light mask is utilized for Cr atom lithography. During a single deposition process, the standing wave frequency is switching from positive detuning to negative detuning alternatively. Results: Nano-gratings fabricated using switching-detuning light mask is successfully replicated with double spatial frequency and self-traceability. Non-uniformity between neighboring Cr lines shows up with a corrected pitch of 107.15 Conclusion: Non-uniformity is mainly caused by the dipole force discrepancy between positive and negative detuning light mask. Therefore, to increase the high uniformity of nano-gratings, the deposition time of negative detuning should be at least twice as the positive detuning. On the other hand, to reduce the pitch uncertainty, it is necessary to reduce the distance between the atom beam and reflection mirror as close as possible. These two significant optimization designs are promising to increase the spatial frequency doubling performance with high uniformity and accuracy.

Super and sub-harmonic synchronization in generalized van der Pol oscillator

Effects of quasiperiodic beatings and sub- and super-harmonic synchronization reveal in plasma physics, optics, acoustics, neurophysiology, etc., but also very often in aero-elasticity of large slender engineering structures, e.g., bridge decks, towers, masts, high rise buildings, ropes, where these phenomena emerge in relation with vortex shedding effects. This applies mainly to quasiperiodic beatings that can be encountered especially in the lock-in regimes, when the vortex frequency becomes close to the structure eigenfrequency ω0 with a small positive or negative detuning. This phenomenon has been thoroughly investigated for the van der Pol system in the previous study by the authors of this paper. However, experimental testing in a wind tunnel showed also other phenomena that can occur in the system resonance zone due to excitations with a multiple or rational fraction frequency leading to sub- or super-harmonic synchronization. All these effects are very dangerous from the viewpoint of reliability and safety of respective systems and hence, a robust theoretical background for design of adequate countermeasures are worthwhile to be developed. In this subsequent study the original sub- and super-synchronization effects are identified and quantified including assessment of their dynamic stability.

Dipole–dipole interactions enhance non-Markovianity and protect information against dissipation**Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0304100 and 2016YFA0302700), the National Natural Science Foundation of China (Grant Nos. 61327901, 11474267, 11774335, and 61322506), the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (Grant No. QYZDY-SSW-SLH003), the Fundamental Research Funds for the Central

Preserving non-Markovianity and quantum entanglement from decoherence effect is of theoretical and practical significance in the quantum information processing technologies. In this context, we study a system S that is initially correlated with an ancilla A, which interacts with the environment E via an amplitude damping channel. We also consider dipole-dipole interactions (DDIs) between the system and ancilla, which are responsible for strong correlations. We investigate the impact of DDIs and detuning on the non-Markovianity and information exchange in different environments. We show that DDIs are not only better than detuning at protecting the information (without destroying the memory effect) but also induce memory by causing a transition from Markovian to non-Markovian dynamics. In contrast, although detuning also protects the information, it causes a transition from non-Markovian to the Markovian dynamics. In addition, we demonstrate that the non-Markovianity grows with increasing DDI strength and diminishes with increasing detuning. We also show that the effects of negative detuning and DDIs can cancel out each other, causing a certain loss of coherence and information.

Nonlinear Dynamics of Exclusive Excited-State Emission Quantum Dot Lasers Under Optical Injection

We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period one (P1), period two (P2), multi-period (MP), and chaotic pulsation (CP). Through mapping these dynamic states in the parameter space of the frequency detuning and the injection coefficient, it can be found that the IL occupies a wide region and the dynamic evolution routes appear in multiple forms. Via permutation entropy (PE) calculation to quantify the complexity of the CP state, the parameter range for acquiring the chaos with high complexity can be determined. Moreover, the influence of the linewidth enhancement factor (LEF) on the dynamical state of the ES-QD laser is analyzed. With the increase of the LEF value, the chaotic area shrinks (expands) in the negative (positive) frequency detuning region, and the IL region gradually shifts towards the negative frequency detuning.

Optical Behavior Analysis of Negative Wavelength Detuning in SMFP-LD and Its Effect on Multi-RF Generation

Injection locking with positive wavelength detuning has been used for a long time for optical signal processing, signal generation, and computing. Recently a new technique, “injection locking with negative wavelength detuning,” has been introduced and has shown its potential on microwave generation. In this paper, we analyze optical behavior of negative injection locking and its impact on multi-RF generation using single-mode Fabry-Perot laser diode (SMFP-LD). SMFP-LD is composed of a commercial multi-mode FP-LD with a built-in external cavity. As compared to conventionally used positive detuning optical injection, the negative detuning optical injection (NOI) shows advantageous differences on the suppression of the dominant mode, side modes, bistability property, and the hysteresis width. The laws of free carrier motion in the laser cavity is leveraged to explain these phenomena. Based on the analysis, the NOI in the SMFP-LD has a distinct advantage for multi-RF generation and switching RF signals. In addition, the output performances of the generated RF signal such as linewidth, power-dependent frequency shifting, and signal-to-noise ratio (SNR) are investigated.

Polariton lasing in InGaN quantum wells at room temperature

In this paper, we report the exciton polaritons in both positive and negative detuning micro cavities based on InGaN multi-quantum wells (MQWs) and the first polariton lasing in InGaN/GaN MQWs at room temperature by utilizing a 4.5λ Fabry-Perot (F-P) cavity with double dielectric distributed Bragg reflectors (DBRs). Double thresholds corresponding respectively to polariton lasing and photonic lasing are observed along with half-width narrowing and peak blue-shifts. The threshold of polariton lasing is about half of the threshold of photonic lasing. Our results paved a substantial way for ultra-low threshold lasers and room temperature Bose-Einstein Condensate (BEC) in nitride semiconductors.

Adiabatic population transfer between electronic states of LiH molecule in two picosecond laser pulses

The population transfer of stimulated Raman adiabatic passage (STIRAP) is investigated using a time-dependent quantum wave packet method. The population is transferred from an initial state to a target state through the interaction of the external laser field with the permanent dipole moment and the transition dipole moment. The laser field is composed of an infrared pulse and a near ultraviolet pulse. The two pulses with small detunings are more efficient to achieve the STIRAP transition. The process of STIRAP is sensitive to the detunings of the two pulses. When the two detunings are the same in a Λ transition or the positive detuning of the pump pulse is equal to the negative detuning of the Stokes pulse in a ladder transition, the final population in the intermediate state can be eliminated and the target population is increased.

Nonlinear quantum optics for spinor slow light

We investigate quantum nonlinear effects at a level of individual quanta in a double tripod atom-light coupling scheme involving two atomic Rydberg states. In such a scheme the slow light coherently coupled to strongly interacting Rydberg states represents a two-component or spinor light. The scheme provides additional possibilities for the control and manipulation of light quanta. A distinctive feature of the proposed setup is that it combines the spin-orbit coupling for the spinor slow light with an interaction between the photons, enabling generation of the second probe beam even when two-photon detuning is zero. Furthermore, the interaction between the photons can become repulsive if the one-photon detunings have opposite signs. This is different from a single ladder atom-light coupling scheme, in which the interaction between the photons is attractive for both positive and negative detunings, as long as the Rabi frequency of the control beam is not too large.

Threshold current temperature dependence of quantum-dot photonic crystal surface-emitting lasers with respect to gain-cavity detuning.

We investigate threshold current temperature dependence of electrically injected quantum-dot (QD) photonic crystal (PC) surface-emitting lasers (SELs) with respect to wavelength detuning between QD gain peak and PC cavity resonance. The lasing emissions cover wavelengths from 1283 nm to 1318 nm. Almost infinite characteristic temperature is realized at certain temperature range for PCSEL with large negative gain-cavity detuning. Moreover, band-edge lasing mode is identified in our "PC slab-on-substrate" structure, and its far-field distribution is characterized as doughnut-shaped beam with azimuthal polarization.

Microwave Frequency Generation, Switching, and Controlling Using Single-Mode FP-LDs

RF signal generation, switching, and reconfiguring are essential and important features for the rapidly developing microwave system, which are usually implemented using independent components or subsystems. In this paper, we propose and demonstrate an optical method to generate and switch the RF frequency at the stage of generation based on control input state using external cavity based single mode Fabry–Perot laser diode. The RF frequency generation, switching, and controlling are based on the principle of injection locking with negative and positive wavelength detuning. In the proposed scheme, a single external beam is simultaneously used to control RF switching as well as to generate RF signal through optical heterodyning of injection locked beams. This eliminates the necessity of two separate external beams to switch and generate RF signal. Based on the logic state of the input control beam, the frequency of the generated RF signal can be changed to another RF frequency within a group of predefined RF bands. In a proof-of-concept experiment, a 2-Gbps, 16-bit nonreturn-to-zero control signal is applied to switch the frequency of the generated RF signal. We obtain the minimum signal to noise power ratio of more than 23 dB, the maximum linewidth of 165 kHz, and rising and falling times of less than 40 ps associated with the RF switching. The tunable range, RF frequency, and RF power variation of the generated RF signals are also observed. Moreover, using random control signals, random sequences of RF frequencies can be generated using the same experimental and hardware setup. Such reconfigurability and flexibility of our system to generate several random RF signals from the same framework enables application of the proposed method in several fields such as secure communication, encryption, and military applications.

Symmetry between repulsive and attractive interactions in driven-dissipative Bose-Hubbard systems

The driven-dissipative Bose-Hubbard model can be experimentally realized with either negative or positive onsite detunings, inter-site hopping energies, and onsite interaction energies. Here we use one-dimensional matrix product density operators to perform a fully quantum investigation of the dependence of the non-equilibrium steady states of this model on the signs of these parameters. Due to a symmetry in the Lindblad master equation, we find that simultaneously changing the sign of the interaction energies, hopping energies, and chemical potentials leaves the local boson number distribution and inter-site number correlations invariant, and the steady-state complex conjugated. This shows that all driven-dissipative phenomena of interacting bosons described by the Lindblad master equation, such as “fermionization” and “superbunching”, can equivalently occur with attractive or repulsive interactions.

Ionization Mechanism of the Generation of Tunable Ultrashort Pulses in the Mid-Infrared Range

The generation of pulses in the mid-infrared range during the ionization of a gas by an intense two-color femtosecond field containing quasimonochromatic components with the frequency ratio close to 2 has been studied. The generation occurs at the detuning frequency equal to the difference between the higher frequency and the doubled lower frequency. It has been shown that the efficiency of the generation is determined both by the magnitude of the detuning frequency and by its sign and is higher at negative detunings. The duration of the generated pulse is determined by the ionization duration, which is much smaller than the duration of the ionizing field, which ensures obtaining few-cycle and subcycle pulses in the mid-infrared range.

Simultaneous Generation of Multiband Signals Using External Cavity-Based Fabry–Perot Laser Diode

Photonic generation of tunable microwave signal has gained the attention of many research communities. Various active components such as vertical-cavity surface-emitting laser diode, semiconductor optical amplifier, and Fabry–Perot laser diode have been used for generating microwave signals using different techniques including side mode injection, feedback injection, and frequency combs. In this paper, we propose and demonstrate a novel approach to generate millimeter wave, simultaneous microwave and millimeter wave, and microwave together with hopping of RF frequency using a single external beam. Furthermore, we demonstrate injecting multiple external beams in a spatial-mode Fabry–Perot laser diode (SMFP-LD) to generate simultaneous multiband signals with negative wavelength detuning. The generated signal ranges from microwave to terahertz. We inject four external beams in SMFP-LD to generate RF frequencies that lie in Ku-, K-, Ka-, V-bands and higher millimeter wave. The frequency of generated signals can be tuned from a few gigahertz to several terahertz. The effects of changing the dominant mode, injecting external beams to different side modes, wavelength and power stability of beating wavelengths, and harmonic generations are analyzed. The maximum linewidth of the generated RF signals with multiple input beams (up to 42.5 GHz) is found to be about 300 kHz.

Absorption of Ultrashort Electromagnetic Pulses by ITO Nanoparticles

The paper investigates the cross-section and probability of absorption of ultrashort electromagnetic pulses by ITO nanoparticles in a dielectric matrix. It discusses the suitability of using the total probability of photoabsorption instead of the probability per unit time for such pulses. It is shown that in the case of negative detuning of the pulse carrier frequency from the plasmon resonance frequency, the photoabsorption probability is a nonlinear function of the pulse duration. For detuning with sufficiently large magnitude, the formation of a maximum is possible in this functional relationship, the position of which depends on the refractive index of the matrix. A method is proposed for measurement of environmental parameters by the analysis of time dependence of this photoprocess. Calculations are performed for a corrected Gaussian pulse and ITO nanoparticles with different doping levels.

Modulation of terahertz-spectrum generation from an air plasma by tunable three-color laser pulses

We theoretically demonstrate that the terahertz-spectrum generation in three-color laser-gas interactions can be effectively manipulated by tuning the laser wavelengths. We show that by positive and negative detuning of one of the color laser wavelengths in the three-color laser pulse, the terahertz spectral range can be greatly expanded, and in particular, the high spectral frequency components emerge. However, the total terahertz energy is maintained at a relatively high level and can even significantly increase. Moreover, we also show that the middle and high spectral frequency components of the terahertz spectrum can be effectively tuned by modulating the relative wavelength of the three-color laser pulses. Finally, our analysis shows that the ionization events play an important role in the intense and shaped terahertz generation.