Lasing Phase Research Articles

Photon-phonon collaboratively pumped laser

In 1917, Einstein considered stimulated photon emission of electron radiation, offering the theoretical foundation for laser, technically achieved in 1960. However, thermal phonons along with heat creation of non-radiative transition, are ineffective, even playing a detrimental role in lasing efficiency. Here, we realize a photon-phonon collaboratively pumped laser enhanced by heat in a counterintuitive way. We observe a laser transition from phonon-free 1064 nm lasing to phonon-pumped 1176 nm lasing in Nd:YVO4 crystal, associated with the phonon-pumped population inversion under high temperatures. Moreover, an additional temperature threshold (Tth) appears besides the photon-pump power threshold (Pth), and a two-dimensional lasing phase diagram is verified with a general relation ruled by Pth = C/Tth (constant C upon loss for a given crystal), similar to Curie’s Law. Our strategy will promote the study of laser physics via dimension extension, searching for highly efficient and low-threshold laser devices via this temperature degree of freedom.

Universality class of the mode-locked glassy random laser

By means of enhanced Monte Carlo numerical simulations parallelized on GPUs we study the critical properties of the spin-glass-like model for the mode-locked glassy random laser, a 44-spin model with complex spins with a global spherical constraint and quenched random interactions. Implementing two different boundary conditions for the mode frequencies we identify the critical points and the critical indices of the random lasing phase transition with finite size scaling techniques. The outcome of the scaling analysis is that the mode-locked random laser universality class is compatible with a mean-field one, though different from the mean-field class of the Random Energy Model and of the glassy random laser in the narrow band approximation, that is, the fully connected version of the present model. The low temperature (high pumping) phase is finally characterized by means of the overlap distribution and evidence for the onset of replica symmetry breaking in the lasing regime is provided.

A quantum model of lasing without inversion

Starting from a quantum description of multiple Λ-type three-level atoms driven with a coherent microwave field and incoherent optical pumping, we derive a microscopic model of lasing from which we move towards a consistent macroscopic picture. Our analysis applies across the range of system sizes from nanolasers to the thermodynamic limit of conventional lasing. We explore the necessary conditions to achieve lasing without inversion in certain regimes by calculating the non-equilibrium steady state solutions of the model at, and between, its microscopic and macroscopic limits. For the macroscopic picture, we use mean-field theory to present a thorough analysis of the lasing phase transition. In the microscopic case, we exploit the underlying permutation symmetry of the density matrix to calculate exact solutions for N three-level systems. This allows us to show that the steady state solutions approach the thermodynamic limit as N increases, restoring the sharp non-equilibrium phase transition in this limit. We demonstrate how the lasing phase transition and degree of population inversion can be adjusted by simply varying the phase of the coherent driving field. The high level of quantum control presented by this microscopic model and the framework outlined here have applications to further understanding and developing nanophotonic technology.

Active optomechanics

Cavity optomechanics explores the coupling between optical and mechanical modes mediated by the radiation pressure force. Unlike the passive scheme, the active optomechanics with optical gain directly imposes the mechanical motion upon the lasing dynamics, unveiling the intrinsic properties determined by the system itself. Here we numerically explore the general characteristics of the active optomechanics. The effects of the mechanical oscillation on the macroscopic laser include introducing multiple unstable regimes in the lasing phase, shifting the laser central frequency, broadening the laser spectrum, and degrading the laser frequency stability. Reducing the optical gain down to one active atom highlights the quantum nature of atom–cavity and photon–phonon interactions. The one-atom optomechanical microlaser does not only emit nonclassical photons but also generate nonclassical photon–phonon pairs. Our work extends the cavity optomechanics to the active fashion, paving the way towards optomechanical light sources for photonic integrated circuits, on-chip quantum communication, and biosensing.

Coherently amplifying photon production from vacuum with a dense cloud of accelerating photodetectors

An accelerating photodetector is predicted to see photons in the electromagnetic vacuum. However, the extreme accelerations required have prevented the direct experimental verification of this quantum vacuum effect. In this work, we consider many accelerating photodetectors that are contained within an electromagnetic cavity. We show that the resulting photon production from the cavity vacuum can be collectively enhanced such as to be measurable. The combined cavity-photodetectors system maps onto a parametrically driven Dicke-type model; when the detector number exceeds a certain critical value, the vacuum photon production undergoes a phase transition from a normal phase to an enhanced superradiant-like, inverted lasing phase. Such a model may be realized as a mechanical membrane with a dense concentration of optically active defects undergoing gigahertz flexural motion within a superconducting microwave cavity. We provide estimates suggesting that recent related experimental devices are close to demonstrating this inverted, vacuum photon lasing phase.

Dissipative Josephson effect in coupled nanolasers

Josephson effects are commonly studied in quantum systems in which dissipation or noise can be neglected or do not play a crucial role. In contrast, here we discuss a setup where dissipative interactions do amplify a photonic Josephson current, opening a doorway to dissipation-enhanced sensitivity of quantum-optical interferometry devices. In particular, we study two coupled nanolasers subjected to phase coherent drivings and coupled by a coherent photon tunneling process. We describe this system by means of a Fokker–Planck equation and show that it exhibits an interesting non-equilibrium phase diagram as a function of the coherent coupling between nanolasers. As we increase that coupling, we find a non-equilibrium phase transition between a phase-locked (PL) and a non-phase-locked (NPL) steady-state, in which phase coherence is destroyed by the photon tunneling process. In the coherent, PL regime, an imbalanced photon number population appears if there is a phase difference between the nanolasers, which appears in the steady-state as a result of the competition between competing local dissipative dynamics and the Josephson photo-current. The latter is amplified for large incoherent pumping rates and it is also enchanced close to the lasing phase transition. We show that the Josephson photocurrent can be used to measure optical phase differences. In the quantum limit, the accuracy of the two nanolaser interferometer grows with the square of the photon number and, thus, it can be enhanced by increasing the rate of incoherent pumping of photons into the nanolasers.

Nonequilibrium states of a plasmonic Dicke model with coherent and dissipative surface-plasmon–quantum-emitter interactions

Hybrid photonic-plasmonic nanostructures allow one to engineer coupling of quantum emitters and cavity modes accounting for the direct coherent and environment mediated dissipative pathways. Using generalized plasmonic Dicke model, we explore the non-equilibrium phase diagram with respect to these interactions. The analysis shows that their interplay results in the extension of the superradiant and regular lasing states to the dissipative coupling regime and an emergent lasing phase without population inversion having boundary with the superradiant and normal states. Calculated photon emission spectra are demonstrated to carry distinct signatures of these phases.

Spontaneous symmetry breaking in the laser transition

In analogy with equilibrium phase transitions, we address the problem of the instability to symmetry-breaking perturbations of systems undergoing a laser transition. The symmetry in question is the $U(1)$ invariance with respect to a phase factor, and the perturbation is a coherent field $E$, coupled to the exciton. At the rate equation level we analyze first the case of a cavity containing a single, two-level emitter, and then a chain of such cavities interacting by photon hopping processes. In both cases spontaneous symmetry breaking takes place when the system is in the lasing phase. For the laser transition, the analogue of the thermodynamic limit is the scaling limit of vanishing cavity loss and light-matter coupling, $\kappa \to 0$, $g \to 0$, so that $g^2/\kappa$ remains finite. We show that in the lasing regime anomalous averages persist in the $E \to 0$ limit, provided that the scaling limit is performed first. Lasing diagnosis based on robust anomalous averages is compared numerically with the familiar coherence criterion $g^{(2)}(0)=1$, and the advantages of the former are discussed.

Quantum sensing close to a dissipative phase transition: Symmetry breaking and criticality as metrological resources

We study the performance of a single qubit-laser as a quantum sensor to measure the amplitude and phase of a driving field. By using parameter estimation theory we show that certain suitable field quadratures are optimal observables in the lasing phase. The quantum Fisher information scales linearly with the number of bosons and thus the precision can be enhanced by increasing the incoherent pumping acting on the qubit. If we restrict ourselves to measurements of the boson number observable, then the optimal operating point is the critical point of the lasing phase transition. Our results point out to an intimate connection between symmetry breaking, dissipative phase transitions and efficient parameter estimation.

Weak lasing in one-dimensional polariton superlattices

Bosons with finite lifetime exhibit condensation and lasing when their influx exceeds the lasing threshold determined by the dissipative losses. In general, different one-particle states decay differently, and the bosons are usually assumed to condense in the state with the longest lifetime. Interaction between the bosons partially neglected by such an assumption can smear the lasing threshold into a threshold domain--a stable lasing many-body state exists within certain intervals of the bosonic influxes. This recently described weak lasing regime is formed by the spontaneously symmetry breaking and phase-locking self-organization of bosonic modes, which results in an essentially many-body state with a stable balance between gains and losses. Here we report, to our knowledge, the first observation of the weak lasing phase in a one-dimensional condensate of exciton-polaritons subject to a periodic potential. Real and reciprocal space photoluminescence images demonstrate that the spatial period of the condensate is twice as large as the period of the underlying periodic potential. These experiments are realized at room temperature in a ZnO microwire deposited on a silicon grating. The period doubling takes place at a critical pumping power, whereas at a lower power polariton emission images have the same periodicity as the grating.

Phase diagram of a polariton laser from cryogenic to room temperature

The signature of the strong-coupling regime is unambiguously evidenced in a GaN-based microcavity (MC) above the polariton lasing threshold ${P}_{thr}$ at room temperature through the observation of the upper polariton branch. The MC system exhibits a renormalization of the polariton dispersion curve, namely, a reduced normal-mode splitting compared to the low-density regime. Next the dependence of ${P}_{thr}$ as a function of exciton-photon detuning is investigated in the 4--340 K temperature range, which allows accessing the polariton lasing phase diagram. The observation of polariton lasing over such a broad range of temperatures reveals a clear transition from a kinetic to a thermodynamic regime with increasing temperature.

Dipole lasing phase transitions in media with singularities in polarizabilities

We show that a divergence in the optical polarizability of a heterogeneous medium with nonlinear amplification and a strong dipole-dipole interaction between particles can lead to a phase transition, for which the dipole momentum of the particles or the dipole radiation rate can be taken as order parameters. The 'dipole laser' [Phys. Rev. A 71, 063812 (2005)] can be used both as a simple example of such a second-order phase transition and to provide a recipe for its analysis. We show that similar phase transitions may be possible for a nanoparticle on the surface of an optically active medium and at the 'Clausius-Mossotti' catastrophe in a bulk heterogeneous medium.

Studies on chaotic multiple-quantum-well laser synchronization via controlling phase and its application in secure communication using external chaos phase shift keying modulation

In this paper, the control of chaotic externalinjection multiplequantumwell laser synchronization via phasecontrollers is presented and external chaos phase shift keying modulation is proposed for secure communication. Chaotic laser synchronization is numerically achieved under controlling by phasecontrollers. Lasing phase shift is controlled via continuous ON/ON chaos shift keying and chaotic laser signal is transmitted by chaos phase shift keying modulation on end. Chaotic laser demodulation is realized by setting a phase shift of the receiver phasecontrollers. ON/ON chaos phase shift keying communications at bit rates of 01 and 05Gbit/s are numerically simulated. ON/ON chaos phase shift keying communication bit rate，the synchronization characterization and the system parameter mismatch are numerically analyzed, in particular.

Atomic coherence and bistable lasers without inversion.

We examine a model of a driven two-level system with injected coherent atoms. We find a set of lasing phase diagrams for the resonant excitations. We show that the laser field in the system is related to the initial preparation of atoms, and that when the degree of this coherence is changed, the system exhibits bistability in the inversionless region. We also discuss the crucial role of atomic coherence in achieving lasing action. \textcopyright{} 1996 The American Physical Society.

Lasing phase diagram for semiconductor surface-emitting lasers

A new tool, a lasing phase diagram, for understanding semiconductor surface-emitting injection lasers has been synthesized. The diagram shows how to design laser resonators which have the lowest possible threshold currents and highest operating efficiencies. To create this diagram, the rate equations describing the photon and electron-hole densities in the laser are solved for the steady-state conditions. The solutions are compactly summarized on a single lasing phase diagram which shows the lasing threshold current and power efficiency contours as functions of two structural parameters (mirror loss and number of quantum wells) in a two-dimensional plane. The plane is separated into three regions corresponding to lasing, marginal lasing, and nonlasing structures. The diagram predicts that, in the high reflectance limit, the threshold current is independent of mirror loss and scales directly with the number of quantum wells in the active region. The phase diagram has been successfully used to understand the lasing characteristics of many different laser structures recently reported.

Helium-neon ring laser (λ = 0.63 μ) stabilized by phase resonances

An experimental investigation was made of the characteristics of an He?Ne ring laser stabilized by phase resonances at the 0.63 ? wavelength. It was highly efficient to use lasing phase resonances as frequency reference points and a frequency stability of 2?10?11 was obtained with an averaging time of 1?10 sec.