Strong Pump Laser Research Articles

Effects of squeezed vacuum field on force sensing for a dissipative optomechanical system

We investigate the force sensing of a mechanical membrane in a dissipative cavity optomechanical system (OMS) driven by a squeezed vacuum field accompanying a strong pump laser. Specifically, the red-detuned laser exhibits a more significant improvement for force sensing compared to the blue-detuned laser. The optimal phase angle contributes to achieving much better force sensing. When injecting a squeezed vacuum field with appropriate squeezing parameter and squeezing phase, the standard quantum limit of force measurement can be easily beaten. Furthermore, the adverse effects of the increase in environment temperature and mechanical damping can be suppressed, simultaneously. This scheme provides a theoretical basics for force sensing of mechanical membranes in dissipative OMS and has potential applications in force feedback control, precision measurement, and force sensor design.

Shaped Microwave Field in a Three-Level Closed Loop Dense Atomic System.

In this work, we investigate the atomic properties of a three-level system under the effect of a shaped microwave field. The system is simultaneously driven by a powerful laser pulse and a weak constant probe that drives the ground state to an upper level. Meanwhile, an external microwave field drives the upper state to the middle transition with shaped waveforms. Hence, two situations are considered: one in which the atomic system is controlled by a strong laser pump and a classical constant microwave field, and another in which both the microwave and pump laser fields are shaped. Finally, for sake of comparison, we investigate the tanh-hyperbolic, the Gaussian and the power of the exponential microwave form in the system. Our results reveal that shaping the external microwave field has a significant impact on the absorption and dispersion coefficient dynamics. In comparison with the classical scenario, where usually the strong pump laser is considered to have a major role in controlling the absorption spectrum, we show that shaping the microwave field leads to distinct results.

Electromagnetically induced transparencies with two transverse Bose–Einstein condensates in a four-mirror cavity

We investigate electromagnetically induced transparencies with two transverse Bose–Einstein condensates in four-mirror optical cavity, driven by a strong pump laser and a weak probe laser. The cavity mode, after getting split from beam splitter, interacts with two independent Bose–Einstein condensates transversely trapped in the arms of the cavity along x-axis and y-axis. The interaction of intra-cavity optical mode excites momentum side modes in Bose–Einstein condensates, which then mimic as two atomic mirrors coupled through cavity field. We show that the probe field photons transition through the atomic mirrors yields to two coupled electromagnetically induced transparency windows, which only exist when both atomic states are coupled with the cavity. Further, the strength of these novel electromagnetically induced transparencies gets increased with an increase in atom-cavity coupling. Furthermore, we investigate the behavior of Fano resonances and dynamics of fast and slow light. We illustrate that the Fano line shapes and dynamics of slow light can be enhanced by strengthening the interaction between atomic states and cavity mode. Our findings not only contribute to the quantum nonlinear optics of complex systems but also provide a platform to test multidimensional atomic states in a single system.

Improving the Signal-to-Noise Ratio of Photonic Frequency Conversion from 852 nm to 1560 nm Based on a Long-Wavelength Laser-Pumped PPLN Waveguide Module

The storage wavelength of quantum nodes based on atomic systems does not match the wavelength of optical fiber communication, which requires the establishment of an efficient conversion system between flying bits and storage bits. In this paper, based on the nonlinear wavelength conversion technology of the periodically poled lithium niobate waveguide, a low-noise conversion of 852-nm photons to 1560-nm photons was achieved by a 1878-nm pump laser. The generation mechanism and transmission mechanism of noise due to nonlinear process are analyzed theoretically. The noise photons introduced by the spontaneous parameter downconversion and spontaneous Raman scattering process of a strong pump laser are experimentally studied. The noise suppression near 1560 nm is realized by the fiber Bragg grating (FBG) filter. In the experiment, when the FBG bandwidth is reduced from 0.257 nm to 0.130 nm, the signal-to-noise ratio (SNR) increases from 52 to 90. Our results show that the SNR can be greatly improved by using a narrower band filter. Therefore, the quantum node is connected to the fiber channel, and the signal can be transmitted over long distances with low loss and high fidelity.

Bichromatic four-wave mixing and quadrature-squeezing from biexcitons in atomically thin semiconductor microcavities

Nonlinear optical effects such as four-wave mixing and generation of squeezed light are ubiquitous in optical devices and light sources. For new devices operating at low optical power, the resonant nonlinearity arising from the two-photon sensitive bound biexciton in a semiconductor microcavity is an interesting prospective platform. Due to the particularly strong Coulomb interaction in atomically thin semiconductors, these materials have strongly bound biexcitons and operate in the visible frequency range of the electromagnetic spectrum. To remove the strong pump laser from the generated light in optical devices or to simultaneously excite non-degenerate polaritons, a bichromatic-pump configuration with two spectrally separated pump lasers is desirable. In this paper, we theoretically investigate spontanous four-wave mixing and quadrature-squeezing in a bichromatically pumped atomically thin semiconductor microcavity. We explore two different configurations that support degenerate and non-degenerate scattering from polaritons into bound biexcitons, respectively. We find that these configurations lead to the generation strongly single- and two-mode quadrature-squeezed light.

Controlling Raman gain with atomic coherence

Raman gain is the optical gain generated by stimulated Raman scattering, which makes weak light amplify possible and can play an important role in weak light communication as well as related field. In this paper, experimentally and theoretically, we have observed the controllable Raman gain under the dressing effects in a coherently prepared N-type four-level atomic configuration. By controlling the detuning of the signal field and the coupling field, the electromagnetically induced transparency (EIT) window can be observed in the signal field. With the incidence of a strong pump laser into the atomic system, the two-photon ultranarrow fluorescence signal can overlap with EIT window by changing the frequency detuning of the pump field, meanwhile, a Raman gain can be induced by placing the signal field at possible large detuning. Such Raman gain can be effectively regulated and optimized by tuning the power of the signal field, pump field and the temperature of the atomic system so as to achieve higher contrast. The multi-parameter regulated higher contrast Raman gain with atomic coherence in atomic thermal system has potential applications in optical communication, superluminal laser and biophotonics.

Optical isolator based on backward Brillouin scattering

We propose to realize an optical isolator based on backward Brillouin scattering in a whispering-gallery-mode (WGM) cavity that supports both traveling optical and acoustic waves. When the WGM cavity is optically driven in one direction, the time-reversal symmetry for light transmission is broken due to the unidirectional photon–phonon coupling. We show that the signal light is either transmitted or completely absorbed depending on whether it propagates in the same or opposite direction as the strong pump laser. The perfect absorption can be interpreted as a phase transition in a parity–time–symmetric Hamiltonian with the balanced gain and loss. The present work paves a way for the realization of an on-chip optical isolator with the high degree of isolation, large bandwidth, and low insertion loss simultaneously.

Quantum Beat of Excitons in the Prolate Ellipsoidal Quantum Dots

In this paper, renormalized wavefunction method was applied to study quantum beats of excitons in the InGaAs/InAlAs prolate ellipsoidal quantum dots (QDs). The obtained results show that, without the pump laser, the exciton absorption intensity is just a smooth curve. In contrast, when the system is illuminated by a strong pump laser resonating with two exciton levels, the oscillation behavior of exciton absorption intensity, which is known as quantum beats of excitons, is observed. That result can be interpreted as an indirect consequence of the Pauli exclusion principle leading to a splitting of the electron levels, which forms two close exciton levels, and if two excitons are excited coherently, the interference of these two excitons will finally form a quantum beat. The study also shows that the geometry shape of the QDs has strong influence on the properties of quantum beats. Changing the period of quantum beats in particular or optical properties in general in QDs thus becomes more flexible through changing their geometry shapes. This is one interested advantage of the ellipsoidal QDs and is expected to increase their applicability more than the spherical QDs.

Controllable Fast and Slow Light in Photonic-Molecule Optomechanics with Phonon Pump.

We theoretically investigate the optical output fields of a photonic-molecule optomechanical system in an optomechanically induced transparency (OMIT) regime, in which the optomechanical cavity is optically driven by a strong pump laser field and a weak probe laser field and the mechanical mode is driven by weak coherent phonon driving. The numerical simulations indicate that when the driven frequency of the phonon pump equals the frequency difference of the two laser fields, we show an enhancement OMIT where the probe transmission can exceed unity via controlling the driving amplitude and pump phase of the phonon driving. In addition, the phase dispersion of the transmitted probe field can be modified for different parametric regimes, which leads to a tunable delayed probe light transmission. We further study the group delay of the output probe field with numerical simulations, which can reach a tunable conversion from slow to fast light with the manipulation of the pump laser power, the ratio parameter of the two cavities, and the driving amplitude and phase of the weak phonon pump.

On the Optical Stark Effect of Excitons in InGaAs Prolate Ellipsoidal Quantum Dots

In this paper, we study the exciton absorption spectra in InGaAs prolate ellipsoidal quantum dots when a strong pump laser resonant with electron quantized levels is active. Our obtained results by renormalized wavefunction theory show that, under suitable conditions, the initial exciton absorption peak is split into two new peaks as the evidence of the existence of the three-level optical Stark effect of excitons. We have suggested an explanation of the origin of the effect as well as investigating the effect of pump field energy, size, and geometric shape of the quantum dots on effect characteristics. The comparison with the results obtained in the spherical quantum dots implies the important role of geometric shape of the quantum structures when we examine this effect.

Theory of femtosecond strong field ion excitation and subsequent lasing in

Delayed cavity-free forward lasing at the wavelengths of 391 and 428 nm was observed in recent experiments in air or pure nitrogen pumped with an intense femtosecond laser pulse at wavelength of 800 nm. The mechanism responsible for the lasing is highly controversial. In this article we propose a model explaining the delayed lasing, which contains two parts: (i) ionization of neutral nitrogen molecules and subsequent excitation of nitrogen ions in a strong pump laser pulse, and (ii) coherent emission of excited ions due to the presence of long-lived polarizations maintained by a weak laser post-pulse and coupling simultaneously ground state to states A2Π u and of singly ionized nitrogen molecules . Two regimes of signal amplification are identified: a signal of a few picosecond duration at low gas pressures and a short (sub-picosecond) signal at high gas pressures. The theoretical model compares favorably with results obtained by different experimental groups.

Controlled bistable dynamics of a four-mirror cavity-optomechanics with two movable mirrors

We investigate the controlled bistable dynamics in a four-mirror optomechanical cavity with two transversely located macroscopic movable mirrors. A strong external pump laser longitudinally drives the cavity, building up a strong cavity mode which interacts with the movable mirrors after getting split from beam splitter. Two mechanical drives externally interact with each of the movable mirrors perturbing their oscillatory motion. We show that the bistable behavior of intra-cavity steady-state photon number, occurring because of the cavity–mirrors coupling, gets significantly enhanced with presence of external mechanical drives. These enhancements can be controlled with the strength of mechanical drive, providing an opportunity to perform optical switching at higher photon number states. Further, we illustrate that the bistable dynamics of movable mirrors are not only being controlled with external mechanical drives, but the increase in mechanical drive of one mirror also suppresses the bistability of other movable mirror with constant (or zero) mechanical drive. We also show the impacts of external mechanical drives on the effective potential of the system.

A study on quantum beats of excitons in GaAs/AlGaAs circular cylindrical quantum wires

This paper presents a theoretical investigation of quantum beats of excitons in GaAs/AlGaAs circular cylindrical quantum wires. A three-level model of excitons, including a ground state and two excited states, has been applied to derive the renormalized wavefunctions and the time-dependent absorption intensity of excitons when the system is irradiated by a strong pump laser resonating with the distance between the two excited-levels. Our results show that a periodic oscillation form of the absorption intensity, obvious evidence of the quantum beat behavior, has appeared. Furthermore, the mechanism of the generation, as well as the effects of the wire radius and the pump laser detuning on the frequency (period) and amplitude of quantum beats, have been explained in detail. These results suggest potential applications in the fabrication of some quantum computation devices.

Ground-state cooling based on a three-cavity optomechanical system in the unresolved-sideband regime* *Project supported by the Research Fund of Tonghua Normal University (Grant No. 202017ND).

In the unresolved sideband regime, we propose a scheme for cooling mechanical resonator close to its ground state in a three-cavity optomechanical system, where the auxiliary cavities are indirectly connected with the mechanical resonator through standard optomechanical subsystem. The standard optomechanical subsystem is driven by a strong pump laser field. With the help of the auxiliary cavities, the heating process is suppressed and the cooling process of the mechanical resonator is enhanced. More importantly, the average phonon number is much less than 1 in a larger range. This means that the mechanical resonator can be cooled down to its ground state. All these interesting features will significantly promote the physical realization of quantum effects in multi-cavity optomechanical systems.

Two-way single-photon-level frequency conversion between 852 nm and 1560 nm for connecting cesium D2 line with the telecom C-band.

A compact setup for two-way single-photon-level frequency conversion between 852 nm and 1560 nm has been implemented with the same periodically-poled magnesium-oxide-doped lithium niobate (PPMgO:LN) bulk crystals for connecting cesium D2 line (852 nm) to telecom C-band. By single-pass mixing a strong continuous-wave pump laser at 1878 nm and the single-photon-level periodical signal pulses in a 50-mm-long PPMgO:LN bulk crystal, the conversion efficiency of ∼ 1.7% (∼ 1.9%) for 852-nm to 1560-nm down-conversion (1560-nm to 852-nm up-conversion) have been achieved. We analyzed noise photons induced by the strong pump laser beam, including the spontaneous Raman scattering (SRS) and the spontaneous parametric down-conversion (SPDC) photons, and the photons generated in the cascaded nonlinear processes. The signal-to-noise ratio (SNR) has been improved remarkably by using the narrow-band filters and changing polarization of the noise photons in the difference frequency generation (DFG) process. With further improvement of the conversion efficiency by employing PPMgO:LN waveguide, instead of bulk crystal, our study may provide the basics for cyclic photon conversion in quantum network.

Optimizing up-conversion single-photon detectors for quantum key distribution.

High-performance single-photon detectors (SPDs) at 1550-nm band are critical for fiber-based quantum communications. Among many types of SPDs, the up-conversion SPDs based on periodically poled lithium niobate waveguides are of great interest. Combined with a strong pump laser, the telecom single-photons are converted into short wavelength ones and detected by silicon-based SPDs. However, due to the difficulty of precise controlling waveguide profile, the direct coupling between a single-mode fiber and the waveguide is not efficient. Here by utilizing fiber taper with proper diameter, optimal mode-matching is achieved and coupling efficiency up to 93% is measured. With an optimized design, a system detection efficiency of 36% and noise counting rate of 90 cps are realized. The maximum detection efficiency is characterized as 40% with a noise counting rate of 200 cps. Numerical simulation results indicate that our device can significantly improve the performance of QKD and extend the communication distance longer than 200 km.

Quantum beat of excitons in spherical semiconductor quantum dots

Abstract This article reports a study on quantum beat of excitons in spherical semiconductor quantum dots. With renormalized wavefunction formulation for a three-level model including ground state level and two excited ones of exciton, quantum beat of excitons is observed to be twice the electron Rabi frequency while a strong resonant pump laser is connecting two exciton excited levels. In addition, dependences of characteristics of quantum beat of excitons on dot radius and pump laser detuning are examined.

Spatial phase modulation and all-optical switching of tris(2`,2-bipyridyl)iron(II) tetrafluoroborate

The spatial self-phase modulation technique was applied to investigate the nonlinear optical properties of Tris(2`, 2-bipyridyl)iron(II) tetrafluoroborate solution. The obtained results show a strong pump laser beam (λ = 532 nm) that could modulate a weak probe laser (λ = 635 nm), indicating for new applications in nonlinear optical modulation. The temporal evolutions of diffraction rings were recorded, at the same time, the collapse effect was observed. Furthermore, our results led to evaluate many nonlinear parameters: the nonlinear refractive index (n2), Δn and thermo-optic coefficient (dn/dT). Our sample is candidate for all-optical switching devices.

Nonlinear optical effect and nonlinear optical mass sensor based on graphene optomechanical system

Graphene, atomically thin two-dimensional (2D) nanomaterial consisting of a single layer of carbon atoms, has received tremendous attention in the past few decades. Graphene may be considered as an excellent nanomaterial for fabricating nanomechanical resonator systems to investigate the quantum behavior of the motion of micromechanical resonators because of its unique properties of low mass density, high frequency, high quality-factor, and intrinsically small size. Additionally, graphene optomechanics based on a bilayer graphene resonator coupled to a microwave on-chip cavity, where light and micromechanical motion interact via the radiation pressure, has been demonstrtated experimentally recently. In this work, we demonstrate theoretically the nonlinear optical effect including optical bistability and four-wave mixing under the regimes woth different parameters and detunings in a graphene resonator-microwave cavity system. When the graphene optomechanics is driven by one strong pump laser beam, we find that the optical bistability can be controlled by tuning the power and the frequency of the pump beam. The four-wave mixing (FWM) phenomenon is also investigated and we find that sharp peaks in the FWM spectrum exactly are located at the resonant frequency of graphene resonator. Therefore, a straight nonlinear optical means for determining the resonant frequency of the graphene resonator is presented. Setting the cavity field resonating with pump field, and then scanning the probe frequency across the cavity frequency, one can easily and exactly obtain the resonant frequency of the resonator from the FWM spectrum. We further theoretically propose a mass sensor based on the graphene optomechanical system. The mass of external nanoparticles deposited onto the graphene resonator can be measured conveniently by tracking the shift of resonant frequency due to mass changing in the FWM spectrum. Compared with optomechanical mass sensors in linear regime, the nonlinear optical mass sensor may be immune to the detection noise. The system may have potential applications in communication networks for frequency conversion and provide a new platform for high sensitive sensing devices.

Timing the recoherences of attosecond electronic charge migration by quantum control of femtosecond nuclear dynamics: A case study for HCCI+

This work suggests an approach to a new target of laser control of charge migration in molecules or molecular ions. The target is motivated by the fact that nuclear motions can not only cause decoherence of charge migration, typically within few femtoseconds, but they may also enable the reappearance of charge migration after much longer times, typically several tens or even hundreds of femtoseconds. This phenomenon is called recoherence of charge migration, opposite to its decoherence. The details depend on the initiation of the original charge migration by an ultrashort strong intense pump laser pulse. It may reappear quasiperiodically, with reference period Tr. We show that a well-designed pump-dump laser pulse can enforce recoherences of charge migration at different target times Tc, for example, at Tc ≈ Tr/2. The approach is demonstrated by quantum dynamics simulations of the laser driven electronic and nuclear motions in the oriented linear cation HCCI+. First, the concept is explained in terms of a didactic one-dimensional (1D) model that accounts for the decisive CI stretch. The 1D results are then confirmed by a three-dimensional model for the complete set of the CH, CC, and CI stretches.