Lasing Regime Research Articles

Triple threshold lasing from a photonic trap in a Te/Se-based optical microcavity

Lasing relies on light amplification in the active medium of an optical resonator. There are three lasing regimes in the emission from a quantum well coupled to a semiconductor microcavity. Polariton lasing in the strong light–matter coupling regime arises from the stimulated scattering of exciton-polaritons. Photon lasing in the weak coupling regime relies on either of two mechanisms: the stimulated recombination of excitons, or of an electron–hole plasma. So far, only one or two out of these three regimes have been reported for a given structure, independently of the material system studied. Here, we report on all three lasing regimes and provide evidence for a three-threshold behavior in the emission from a photonic trap in a Se/Te-based planar microcavity comprising a single CdSe/(Cd,Mg)Se quantum well. Our work establishes the so far unsettled relation between lasing regimes that differ by their light-matter coupling strength and degree of electron–hole Coulomb correlation.

Active phase mode locking in a cavity with a controllable Michelson interferometer

This paper presents an experimental and numerical study of the subnanosecond operating regime of a solid-state laser that uses active phase modulation for mode locking and Q-switching of the cavity. The output mirror of the laser cavity, which contains a solid-state quantron with continuous diode pumping, is made in the form of a controllable Michelson interferometer one of whose arms contains an electro-optic phase modulator that dynamically modulates the interferometer’s transmission. The modulation consists of a fast harmonic nanosecond component for mode locking and a slow component in the form of a frequency sequence of microsecond pulses that control the width of the envelope of a train of nanosecond pulses. The paper describes the features of this cavity, analyzes its advantages and disadvantages, and discusses the prospects of developing the given technology for efficient pulse compression, with the possibility of controlling the pulse width by varying the electrical parameters of the electro-optic-modulator driver.

Room Temperature Lasing of Single-Mode Arched-Cavity Quantum-Cascade Lasers

Single-mode lasing at room temperature in quantum-cascade lasers (QCLs) with arched cavity design has been demonstrated. The output optical power in single-mode lasing regime at ~7.7-μm lasing wavelength was above 6 mW with a side-mode suppression ratio of up to 25 dB. The QCL heterostructure for the arched cavities was grown by molecular-beam epitaxy (MBE) based on a heterojunction of In0.53Ga0.47As/Al0.48In0.52As solid alloys, lattice-matched with InP substrate, and InP layers performing the function of waveguide claddings.

First demonstration of ARC-accelerated proton beams at the National Ignition Facility

New short-pulse kilojoule, Petawatt-class lasers, which have recently come online and are coupled to large-scale, many-beam long-pulse facilities, undoubtedly serve as very exciting tools to capture transformational science opportunities in high energy density physics. These short-pulse lasers also happen to reside in a unique laser regime: very high-energy (kilojoule), relatively long (multi-picosecond) pulse-lengths, and large (10s of micron) focal spots, where their use in driving energetic particle beams is largely unexplored. Proton acceleration via Target Normal Sheath Acceleration (TNSA) using the Advanced Radiographic Capability (ARC) short-pulse laser at the National Ignition Facility in the Lawrence Livermore National Laboratory is demonstrated for the first time, and protons of up to 18 MeV are measured using laser irradiation of >1 ps pulse-lengths and quasi-relativistic (∼1018 W/cm2) intensities. This is indicative of a super-ponderomotive electron acceleration mechanism that sustains acceleration over long (multi-picosecond) time-scales and allows for proton energies to be achieved far beyond what the well-established scalings of proton acceleration via TNSA would predict at these modest intensities. Furthermore, the characteristics of the ARC laser (large ∼100 μm diameter focal spot, flat spatial profile, multi-picosecond, relatively low prepulse) provide acceleration conditions that allow for the investigation of 1D-like particle acceleration. A high flux ∼ 50 J of laser-accelerated protons is experimentally demonstrated. A new capability in multi-picosecond particle-in-cell simulation is applied to model the data, corroborating the high proton energies and elucidating the physics of multi-picosecond particle acceleration.

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.

Experimental electric field visualisation of multi-mode dynamics in a short cavity swept laser designed for OCT applications.

An experimental study into the modal dynamics of a short cavity, fast frequency-swept laser is presented. This commercially available external cavity swept source is designed for use in optical coherence tomography (OCT) applications and displays a number of dynamic lasing regimes during the course of the wavelength sweep. Interferometric full electric field reconstruction is employed, allowing for measurement of the laser operation in a time-resolved, single-shot manner. Recovery of both the phase and intensity of the laser output across the entire sweep enables direct visualization of the laser instantaneous optical spectrum. The electric field reconstruction technique reveals the presence of multi-mode dynamics, including coherent mode-locked pulses. During the main part of the imaging sweep, the laser is found to operate in a second harmonic sliding frequency mode-locking regime. Examination of the modal evolution of this coherent regime reveals evidence of previously unobserved frequency switching dynamics.

Study of dielectric coatings for broadband operation of surface-emitting semiconductor lasers

We investigate antireflection (AR) coating materials for two different operation lasing regimes requiring broad spectral bandwidth. We characterize high-power continuous-wave (CW) wavelength-tunable vertical-external-cavity surface-emitting semiconductor lasers and their passive mode-locking capabilities when using semiconductor saturable absorber mirrors. One laser gain design was investigated with different single dielectric layers as AR coatings. The dielectric coating materials used were SiO2, Al2O3, Ta2O5, and TiO2. The AR coating was designed to reduce pump reflection and increase the confinement factor of the microcavity. Average power of 4.6 W in CW and a total wavelength tuning range of 42 nm has been observed with the SiO2-coated structure. The shortest pulse of 708 fs was also observed for the SiO2-coated structure, with a corresponding CW wavelength tuning range of 36 nm.

Electrically Controlled Neuron-Like Spiking Regimes in Vertical-Cavity Surface-Emitting Lasers at Ultrafast Rates

We report experimentally on the electrically controlled, tunable, and repeatable neuron-like spiking regimes generated in an optically injected vertical-cavity surface-emitting laser (VCSEL) operating at the telecom wavelength of 1300 nm. These fast spiking dynamics (obtained at sub-nanosecond speed rates) demonstrate different behaviors observed in biological neurons such as thresholding, phasic and tonic spiking, and spike rate and spike latency coding. The spiking regimes are activated in response to external stimuli (with controlled strengths and temporal duration) encoded in the bias current applied to a VCSEL subject to continuous wave optical injection. These results reveal the prospect for fast (>7 orders of magnitude faster than neurons), novel, electrically controlled spiking photonic modules for future neuromorphic computing platforms.

Dynamical multistability in a quantum-dot laser

We study the dynamical multistability of a solid-state single-atom laser implemented in a quantum-dot spin valve. The system is formed by a resonator that interacts with a two-level system in a dot in contact with two ferromagnetic leads of antiparallel polarization. We show that a spin-polarized current provides high-efficiency pumping leading to regimes of multistable lasing, in which the Fock distribution of the oscillator displays a multi-peaked distribution. The emergence of multistable lasing follows from the breakdown of the usual rotating-wave approximation for the coherent spin-resonator interaction which occurs at relatively weak couplings. The multistability manifests itself directly in the charge current flowing through the dot, switching between distinct current levels corresponding to the different states of oscillation.

Methodical engineering of defects in MnXZn1-X O(x = 0.03, and 0.05) nanostructures by electron beam for nonlinear optical applications: A new insight

A series of MnxZn1-xO (x = 0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in e-beam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters.

Одночастотная генерация арочных квантово-каскадных лазеров при комнатной температуре

AbstractSingle-mode lasing at room temperature in quantum-cascade lasers (QCLs) with arched cavity design has been demonstrated. The output optical power in single-mode lasing regime at ~7.7-μm lasing wavelength was above 6 mW with a side-mode suppression ratio of up to 25 dB. The QCL heterostructure for the arched cavities was grown by molecular-beam epitaxy (MBE) based on a heterojunction of In_0.53Ga_0.47As/Al_0.48In_0.52As solid alloys, lattice-matched with InP substrate, and InP layers performing the function of waveguide claddings.

Mode-locked fiber laser in the C-band region for dual-wavelength ultrashort pulses emission using a carbon nanotube saturable absorber

A saturable absorber is commonly employed to generate an ultrashort laser with a mode-locking scheme. In an erbium-doped fiber laser system, the laser regimes of either 1530 or 1550 nm wavelength are procured based on the absorption profile of the erbium-doped fiber. The absorption of the erbium-doped fiber is designed to emit at both wavelengths by controlling the net gain of the laser cavity. Subsequently, simultaneous erbium-doped fiber laser emission is attained at 1533.5 and 1555.1 nm with the pulse duration of 910 and 850 fs, respectively. Therefore, this work maximizes the output portfolios of a mode-locking fiber laser for dual-wavelength ultrashort pulses emission.

Lasing in the superradiant crossover regime

A new class of laser, which harnesses coherence in both light and atoms, is possible with the use of ultra-cold alkaline earth atoms trapped in an optical lattice inside an optical cavity. Different lasing regimes, including superradiance, superradiant and conventional lasing, are distinguished by the relative coherence stored in the atoms and in the cavity mode. We analyze the physics in two different experimentally achievable regions of the superradiant lasing regime. Our calculations confirm the narrow linewidth of superradiant lasing for the doubly forbidden clock transition ${}^3 P_0 \to {}^1 S_0$ of strontium-87 atoms. Under strong driving of the dipole-forbidden transition ${}^3 P_1 \to {}^1 S_0$ of strontium-88 atoms the superradiant linewidth narrows further due to the coherent excitation of the cavity field.

Comparison of mode-locking regimes in a holmium fibre laser

A comparison has been performed for two mode-locking regimes in an all-fibre holmium laser: locking due to nonlinear polarisation rotation (NPR) and hybrid mode-locking (NPR with application of single-walled carbon nanotubes). The characteristics of pulsed lasing in both regimes are investigated. Pulsed lasing is obtained at wavelengths of 2072 and 2082 nm, with FWHM values of 3.7 and 3.3 nm, respectively. The pulse width in both cases does not exceed 1.5 ps. The pulse energies in the NPR mode-locking and hybrid mode-locking regimes are 0.4 and 0.3 nJ, respectively. It is shown that the signal-to-noise ratio in the case of hybrid mode-locking is 3 dB better than that implemented under conditions of NPR mode-locking. A possibility of self-starting a laser system by applying hybrid mode-locking is indicated.

Delayed Transition to Coherent Emission in Nanolasers with Extended Gain Media

The realization of high-$\beta$ lasers is one of the prime applications of cavity-QED promising ultra-low thresholds, integrability and reduced power consumption in the field of \textit{green photonics}. In such nanolasers spontaneous emission can play a central role even above the threshold. By going beyond rate-equation approaches, we revisit the definition of a laser threshold in terms of the input-output characteristics and the degree of coherence of the emission. We demonstrate that there are new regimes of cavity-QED lasing, realized e.g. in high-$Q$ nanolasers with extended gain material, for which the two can differ significantly such that coherence is reached at much higher pump powers than required to observe the thresholdlike intensity jump. Against the common perception, such devices do not benefit from high-$\beta$ factors in terms of power reduction, as a significant amount of stimulated emission is required to quieten the spontaneous emission noise.

Thermal Switching of Lasing Regimes in Heavily Doped Er3+ Fiber Lasers

A pulsed regime of short-cavity, heavily erbium-doped fiber lasers is of high interest for its possible applications in telecommunications and sensorics. Here, we demonstrate and compare these lase...

A Microfiber Knot Incorporating a Tungsten Disulfide Saturable Absorber Based Multi-Wavelength Mode-Locked Erbium-Doped Fiber Laser

A novel multi-wavelength mode-locked Erbium-doped fiber laser with tungsten disulfide (WS2) combined with a microfiber knot is described. This hybrid fiber structure facilitates strong light matter interaction between the saturated absorption of the WS2 material and high optical non-linearity of the microfiber knot. It is demonstrated experimentally that the novel fiber laser works stably in the absence of an external comb filter, with the generation of stable multi-wavelength picosecond pulses. In the multi-wavelength lasing regime, up to seven-wavelength stable mode-locked pulses are obtained using a polarization controller with the pump power at ∼250 mW. The pulse period and the pulsewidth are 188.7 ns and 16.3 ps, respectively. In addition, the number of multi-wavelength lasing channels can be changed by simply adjusting the microfiber knot size. Experimental results show the laser to have a stable output over 12-h recording period. The results of this investigation demonstrate that the optical microfiber knot with a WS2 overlay based fiber laser device can operate as a highly nonlinear optical component and a saturable absorber. The proposed multi-wavelength lasing device can therefore be widely used for non-linear and ultrafast photonics and has a number of advantages compared to similar devices using more conventional technologies, including low cost and good stability.

Tunable and switchable C-band and L-band multi-wavelength erbium-doped fiber laser employing a large-core fiber filter

In this paper, we propose and experimentally demonstrate a C- and L-band erbium-doped fiber laser (EDFL) with tunable single-, dual- and triple-wavelength lasing emissions. A tapered structure large-core fiber filter (LCFF) is inserted to serve as tuning component and wavelength selector for tunable and stable multi-wavelength oscillations. Based on the axial strain response of LCFF, two tunable triple-wavelength regimes within the range from 1558.71 to 1579.81 nm are obtained with side mode suppression ratio (SMSR) as high as 55 dB. Moreover, tunable single- and dual-wavelength regimes are also achieved with total tuning range of 11 nm and 6.23 nm, respectively. The tuning step for overall laser regimes is 0.02 nm, and the maximum wavelength sensitivity reaches to 1.87 pm/με. In addition, this proposed versatile EDFL is proved to be very stable since the lasing wavelength shifts and power fluctuations are less than 0.02 nm and 0.78 dB during an hour.

Reducing the sensitivity of semiconductor ring lasers to external optical injection using selective optical feedback

We numerically investigate the influence of an integrated filtered optical feedback on the behavior of a semiconductor ring laser subject to external optical injection. The optical injection is spectrally directed at one of the non-lasing longitudinal modes of the laser. This so-called side-mode injection can cause wavelength switching, directional switching, and changes in the dynamical regime of the semiconductor ring laser. Such changes are often unwanted as they can affect the stability and the performance of the semiconductor ring laser. We investigate to what extent these undesired effects can be avoided by stabilizing the laser using on-chip filtered feedback. A two-directional mode model is used to investigate the dynamical behavior of the semiconductor ring laser under the simultaneous effect of the external optical injection and the integrated feedback. The results show that on-chip filtered optical feedback can be used to reduce the sensitivity of the semiconductor ring laser to external optical injection.

Dual-wavelength quasi-mode-locked regimes of an Er-doped fiber ring laser

We demonstrate the dual-wavelength quasi mode-locked operation of a passively mode-locked Er-doped fiber ring laser with twisted fiber in the cavity and a double-pass amplifier with a Faraday mirror. The configuration allows very strict control of the polarization. We observed synchronous dual-wavelength generation of noise-like pulses (NLP) with spectra centered at 1534 nm and 1562 nm. Rotation of the azimuth of the radiation propagating in the cavity caused a switching between the generation of NLPs and packets of pulses with typical solitons spectrum. In the latter regime, we observed partially synchronous sub-pulses at two different wavelengths.