Cavity Lifetime Research Articles

Class-C semiconductor lasers with time-delayed optical feedback.

We perform a linear stability analysis and numerical bifurcation diagrams of a class-C laser with time-delayed optical feedback. We employ a rate equation system based on the Maxwell-Bloch equations, and study the influence of the dephasing time on the laser dynamics. We find a stabilizing effect of an intermediate dephasing time, i.e. when moving from a class-B to a class-C laser. At long dephasing times, a destabilization of the laser solution occurs by a feedback-induced unlocking of Rabi oscillations at the second laser threshold. We predict an optimum resistance to time-delayed optical feedback for dephasing times close to the photon cavity lifetime. This article is part of the theme issue 'Nonlinear dynamics of delay systems'.

Dynamic cavity effects in topological insulator Bi2Te3 based passive Q-switched solid state laser

In this work, a comprehensive investigation of dynamic evolution for pulsed solid state laser using topological insulator as saturable absorber (SA) is reported. Without material damage, dynamic transition from Q-switched (QS) state to continuous wave (CW) state in the laser cavity is observed when the pumping rate to the Nd3+:YAG laser crystal increases. With a sufficiently large pumping rate, the initiated laser spiking damps and relaxes to CW state similar to a laser system without intra-cavity SA. Formulated by well-known laser rate equations, analysis of the perturbations around fixed points reveals the instability spectrum that is able to explain the observed transition in experiments. Theoretically, the parameters space to support QS operation are given in terms of the ratio of saturation intensity of laser gain media over the saturation intensity of SA, pumping speed, the ratio of relaxation time of laser gain media over cavity lifetime and the modulation depth of the SA. The result of this work suggests a simple approach to understand passive Q-switched (PQS) laser with SAs of low saturation intensity and guidelines to the design of laser system employing low-saturation materials as SA, such as two-dimensional TI material.

Coupling analysis of high Q resonators in add-drop configuration through cavity ringdown spectroscopy

An original method able to fully characterize high-Q resonators in an add-drop configuration has been implemented. The method is based on the study of two cavity ringdown (CRD) signals, which are produced at the transmission and drop ports by wavelength sweeping a resonance in a time interval comparable with the photon cavity lifetime. All the resonator parameters can be assessed with a single set of simultaneous measurements. We first developed a model describing the two CRD output signals and a fitting program able to deduce the key parameters from the measured profiles. We successfully validated the model with an experiment based on a fiber ring resonator of known characteristics. Finally, we characterized a high-Q, home-made, MgF2 whispering gallery mode disk resonator in the add-drop configuration, assessing its intrinsic and coupling parameters.

Theory of a Quantum Scanning Microscope for Cold Atoms.

We propose and analyze a scanning microscope to monitor "live" the quantum dynamics of cold atoms in a cavity QED setup. The microscope measures the atomic density with subwavelength resolution via dispersive couplings to a cavity and homodyne detection within the framework of continuous measurement theory. We analyze two modes of operation. First, for a fixed focal point the microscope records the wave packet dynamics of atoms with time resolution set by the cavity lifetime. Second, a spatial scan of the microscope acts to map out the spatial density of stationary quantum states. Remarkably, in the latter case, for a good cavity limit, the microscope becomes an effective quantum nondemolition device, such that the spatial distribution of motional eigenstates can be measured backaction free in single scans, as an emergent quantum nondemolition measurement.

Erratum: Micromachined Integrated Quantum Circuit Containing a Superconducting Qubit [Phys. Rev. Applied 7 , 044018 (2017)

We present a device demonstrating a lithographically patterned transmon integrated with a micromachined cavity resonator. Our two-cavity, one-qubit device is a multilayer microwave integrated quantum circuit (MMIQC), comprising a basic unit capable of performing circuit-QED (cQED) operations. We describe the qubit-cavity coupling mechanism of a specialized geometry using an electric field picture and a circuit model, and finally obtain specific system parameters using simulations. Fabrication of the MMIQC includes lithography, etching, and metallic bonding of silicon wafers. Superconducting wafer bonding is a critical capability that is demonstrated by a micromachined storage cavity lifetime $34.3~\mathrm{\mu s}$, corresponding to a quality factor of 2 million at single-photon energies. The transmon coherence times are $T_1=6.4~\mathrm{\mu s}$, and $T_2^{Echo}= 11.7~\mathrm{\mu s}$. We measure qubit-cavity dispersive coupling with rate $\chi_{q\mu}/2\pi=-1.17~$MHz, constituting a Jaynes-Cummings system with an interaction strength $g/2\pi=49~$MHz. With these parameters we are able to demonstrate cQED operations in the strong dispersive regime with ease. Finally, we highlight several improvements and anticipated extensions of the technology to complex MMIQCs.

Emission characteristics of high-gain GaN-based Vertical-Cavity Surface-Emitting Lasers

GaN-based vertical-cavity surface-emitting lasers (VCSELs) with high optical gain and short cavity lifetime are favorable for the generation of ultra-short pulses in the blue and green regions. In our previous works, 6 and 2 picosecond short-pulses have been generated from gain-switched InGaN VCSELs with 3- and 10-period InGaN/GaN quantum wells (QWs) in the active layers by using an up-conversion measurement system. To further increase the gain of the VCSEL for the generation of even shorter pulses, 20-period InGaN/GaN QWs samples were fabricated. The emission characteristics of these high-gain VCSELs were investigated and analyzed under the optical pumping at room temperature.

Experimental Investigation of Cavitation Behind a Circular Cylinder in Cross-Flow

Cavitation behind a circular cylinder is studied with the aid of highly time-resolved images at a constant Reynolds number of 64,000. Apart from recording the overall cavitation activity behind the cylinder, the study also delves into the dynamics of individual cavities. The length of cavity scales with cavitation number and this scaling is similar to the existing results obtained in flow regimes different from that presented here. Dynamics of individual cavities show distinct phases of cavity formation, growth, and collapse. At lower cavitation numbers, cavity collapse was followed by a rebounce. Variation of area normalized by the length of cavity shows self similarity in the growth phase of cavities for different cavitation numbers. Thus, the cavity length is the suitable length scale for dynamics of cavities, at least for the growth phase. The cavity lifetime scales inversely with the square of cavitation number. Dynamics of individual small cavity captured at higher frame rates was found to be similar to that of an isolated bubble. In this case, a rapid collapse follow a more gradual expansion phase, unlike that shown by larger cavities.

Ultra-low threshold polariton condensation.

We demonstrate the condensation of microcavity polaritons with a very sharp threshold occurring at a two orders of magnitude pump intensity lower than previous demonstrations of condensation. The long cavity lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or "polariton lasing" has long been proposed as a promising source of coherent light at a lower threshold than traditional lasing, and these results indicate some considerations for optimizing designs for lower thresholds.

Dynamical Casimir effect of phonon excitation in the dispersive regime of cavity optomechanics

In this paper, we theoretically propose and investigate a feasible experimental scheme for realizing the dynamical Casimir effect (DCE) of phonons in an optomechanical setup formed by a ground-state precooled mechanical oscillator (MO) inside a Fabry-P{\'e}rot cavity, which is driven by an amplitude-modulated classical laser field in the dispersive (far-detuned) regime. The time modulation of the driving field leads to the parametric amplification of the mechanical vacuum fluctuations of the MO, which results in the generation of Casimir phonons over time scales longer than the cavity lifetime. We show that the generated phonons exhibit quadrature squeezing, bunching effect, and super-Poissonian statistics which are controllable by the externally modulated laser pump. In particular, we find that the scheme allows for a perfect squeezing transfer from one mechanical quadrature to another when the laser frequency is varied from red detuning to blue detuning. Moreover, by analyzing the effect of the thermal noise of the MO environment, we find that there exists a critical temperature above which there is no phonon quadrature squeezing to occur. We also show that in the presence of time modulation of the driving laser the linewidth narrowing of the displacement spectrum of the MO can be considered as a signature of the generation of Casimir phonons.

The effect of pulsewidth of pumping pulse on the stability of distributed feedback dye laser

The generation of a single and stable picosecond pulse by distributed feedback dye laser is investigated in this work. The numerical result for the rate equation system that includes the thermal effects in the lasing medium is provided. By applying this model to Rhodamine 6G, it is found that considerable improvement in the stability of the laser can be achieved by pumping the system with narrower laser pulses. The simulation shows that if the dye solution is pumped by sub-200 ps pulse, the laser can be operated in single-pulse output mode with acceptable stability in pulsewidth over a long range of pumping intensity. This result is confirmed by a more complicated model composed of non-averaged Maxwell and rate equations. Even though the thermal effects do not play a significant role in equivalent cavity lifetime, they result in considerable wavelength shift toward the shorter wavelengths.

Optomechanical sensing of liquids outside standard fibers using forward stimulated Brillouin scattering

The analysis of chemical species is one of the most fundamental and long-standing challenges in fiber-optic sensors research. Existing sensor architectures require a spatial overlap between light and the substance being tested and rely either on structural modifications of standard fibers or on specialty photonic crystal fibers. In this work, we report an optomechanical fiber sensor that addresses liquids outside the cladding of standard, 8/125 μm single-mode fibers with no structural intervention. Measurements are based on forward stimulated Brillouin scattering by radial, guided acoustic modes of the fiber structure. The acoustic modes are stimulated by an optical pump pulse and probed by an optical signal wave, both confined to the core. The acoustic vibrations induce a nonreciprocal phase delay to the signal wave, which is monitored in a Sagnac interferometer loop configuration. The measured resonance frequencies and excitation strengths of individual modes agree with the predictions of a corresponding quantitative analysis. The acoustic reflectivity at the outer cladding boundary and the acoustic impedance of the surrounding medium are extracted from cavity lifetime measurements of multiple modes. The acoustic impedances of deionized water and ethanol are measured with better than 1% accuracy. The measurements successfully distinguish between aqueous solutions with 0, 4%, 8%, and 12% concentrations of dissolved salt. The new fiber-sensing paradigm might be used in the monitoring of industrial processes involving ionic solutions.

Droplet impact cavity film thickness measurements versus time after drop impact and cavity radius for thin static residual liquid layer thicknesses

Comprehensive measurements are presented of the sub-cavity liquid film thickness for single droplet impacts into a static residual liquid layer, measured both versus the radius away from the cavity impact centerline and the local time since initial contact of the drop with the static residual liquid layer. Droplet Weber and Reynolds numbers are representative of the highest-energy droplets for a water spray of interest, with Weber numbers ranging between 140 and 1000. These high-impact-energy droplets create drop impact cavities with the longest cavity lifetimes, thinnest sub-cavity liquid films, and smallest sub-cavity liquid volumes, all of which are expected to contribute to the droplet impact cavities being both a significant source of enhanced transient local heat flux into the sub-cavity liquid volumes, as well as locations of early local surface dry out.Sub-cavity liquid film thickness is essentially constant over the inner radial portion of the cavity, but is significantly thinner at large cavity radius, somewhat inboard of the inner crown wall. The inner, constant thickness region ranges between 62% and 85% of the maximum cavity radius in extent, with an average size of 72% of maximum cavity radius. The thickness of this inner, constant thickness region ranges between 100μm and 162μm, with an average value of 126.5μm, or around 4% of the nominal droplet diameter of 3mm. This thickness varies by only around 3% of its average value for single values of the Weber number and static residual liquid layer thickness. At the end of cavity formation, the thinner regions farther outboard in the cavity are about 23% thinner than the sub-cavity film thickness in the inner region; but later, during the collapse of the crown, the thinner outboard region averages 34% less than the thickness in the inner, constant thickness region.Two major data accuracy limitations are discussed, and approximate error magnitudes are estimated. Drop-to-drop uncertainty in impact location and the uncertainty in the level of three-dimensionality of the cavity retraction process are both inherent limitations in the present liquid film thickness point-measurement method; these limitations could be avoided if a global thickness measurement over the entire cavity surface could be obtained; e.g., via stereo high-speed imaging.

An ultra-narrow linewidth solution-processed organic laser.

Optically pumped lasers based on solution-processed thin-film gain media have recently emerged as low-cost, broadly tunable, and versatile active photonics components that can fit any substrate and are useful for, e.g., chemo- or biosensing or visible spectroscopy. Although single-mode operation has been demonstrated in various resonator architectures with a large variety of gain media—including dye-doped polymers, organic semiconductors, and, more recently, hybrid perovskites—the reported linewidths are typically on the order of a fraction of a nanometer or broader, i.e., the coherence lengths are no longer than a few millimeters, which does not enable high-resolution spectroscopy or coherent sensing. The linewidth is fundamentally constrained by the short photon cavity lifetime in the standard resonator geometries. We demonstrate here a novel structure for an organic thin-film solid-state laser that is based on a vertical external cavity, wherein a holographic volume Bragg grating ensures both spectral selection and output coupling in an otherwise very compact (∼cm3) design. Under short-pulse (0.4 ns) pumping, Fourier-transform-limited laser pulses are obtained, with a full width at half-maximum linewidth of 900 MHz (1.25 pm). Using 20-ns-long pump pulses, the linewidth can be further reduced to 200 MHz (0.26 pm), which is four times above the Fourier limit and corresponds to an unprecedented coherence length of 1 m. The concept is potentially transferrable to any type of thin-film laser and can be ultimately made tunable; it also represents a very compact alternative to bulky grating systems in dye lasers.

Lasing dynamics of super and sub luminal lasers.

We study theoretically the lasing properties and the cavity lifetime of super and sub-luminal lasers. We find that obtaining the necessary conditions for superluminal lasing requires care and that a laser operating under these conditions can under some conditions tend towards bi-frequency lasing. In contrast, conditions for a subluminal laser are less stringent, and in most situations its steady-state properties are well predicted by the self-consistent single-frequency laser equations. We also study the relaxation time of power perturbation in super and sub-luminal lasers using a finite-difference-time-domain tool and present the impact of the lasing power, the group velocity and the dispersion properties of the cavity on the relaxation dynamic of such perturbations. For the subluminal laser, we find that the time constant changes by a factor that is close to the group index. In contrast, for the superluminal laser, we find that the time constant does not change by the factor given by the group index, and remains close to or above the value for an empty cavity. These finding may be interpreted to imply that the quantum noise limited linewidth of the subluminal laser decreases with increasing group index, while the same for the superluminal laser does not increase with decreasing group index. The implications of these findings on the sensitivity of sensors based on these lasers are discussed in details.

Effect of Cavity Lifetime Variation on the Static and Dynamic Properties of 1.3-μm Wafer-Fused VCSELs

We investigate experimentally the impact of photon cavity lifetime variations on the static and dynamic performance of high-speed 1.3-μm wavelength wafer–fused vertical-cavity surface-emitting lasers (VCSELs). The photon lifetime is modified by decreasing the top mirror reflectivity either by shallow-surface etching or by Bragg-reflector layer-pair removal. Significant improvements in both static and dynamic VCSEL performance as well as the extraction of internal VCSEL device parameters are achieved.

Strong photon blockade with intracavity electromagnetically induced transparency in a blockaded Rydberg ensemble

We consider the dynamics of intracavity electromagnetically induced transparency (EIT) in an ensemble of strongly interacting Rydberg atoms. By combining the advantage of variable cavity lifetimes with intracavity EIT and strongly interacting Rydberg dark-state polaritons, we show that such intracavity EIT system could exhibit very strong photon blockade effect.

Sub-cavity liquid volume beneath spray droplet impacts into static liquid layers, and initial estimates of the heat flux required to dry out this volume

The time variation of the sub-cavity liquid volume beneath individual droplet impact cavities was measured for ranges of drop Weber and Reynolds numbers that match those for a full cone spray nozzle of interest. Cavity lifetime was also measured. These results will be used in a Monte-Carlo model of the spray cooling process that is currently under development. Droplet Weber numbers were varied between 140 and 1000. Corresponding Reynolds numbers ranged between approximately 1200 and 3600. These ranges matched Phase Doppler results that were obtained for the water spray under study. Thickness of the static liquid layer into which the single droplets impacted was varied between 0.2 and 1.0 times the droplet diameter.The measured sub-cavity liquid volume generally was between 60% and 80% of the original droplet volume over much of the cavity lifetime. Increasing the static liquid layer thickness increased this plateau value of the sub-cavity liquid volume between these lower and upper bounds, for Weber numbers greater than around 400. Sub-cavity liquid volume also increased somewhat as Weber number was increased. The cavity lifetime increased significantly as Weber number increased.The sub-cavity liquid volume and cavity lifetime results were scaled to values for the corresponding spray droplets at equal (We, Re). These were then used in an energy balance between the energy transferred through a heated wall to the sub-cavity liquid and the sum of the sensible heating and latent heat required to dry out the spray drop sub-cavity liquid volume within the cavity lifetime. These computed heat fluxes to dry out the drop impact cavities were then used to estimate the overall average heat flux for a heated surface that would dry out these individual spray droplet impact cavities. The resulting average heat flux values were between 400W/cm2 and 800W/cm2. These predictions are similar to the range of CHF values reported in the literature for water, of 500W/cm2 to 1000W/cm2.

Improving cavity lifetime by electromagnetic-induced-transparency-like meta-atoms

In this paper, lifetime enhancement in a microstrip photonic crystal (PC) cavity by embedding electromagnetic-induced-transparency (EIT)-like meta-atoms is reported. Both microwave experiments and numerical simulations confirm that cavity lifetime can be lengthened about four times, with enhanced Q-factor simultaneously. Further study on electromagnetic field distribution reveals that these enhancements are mainly originated from the confinement along the propagating direction provided by PC cavity and the in-unit localization from the EIT-like meta-atoms. Moreover, study on the group delay shows that by introducing multiple EIT-like meta-atoms, these improvements of cavity lifetime and Q-factor can even be superimposed. As these advantages are not at a cost of extra device volume, the design principle of composite PC–EIT structure is promising to be applied in nonlinear optical devices, optical storage, lasing optics, and so on.

Control of cavity lifetime of 1.5 µm wafer-fused VCSELs by digital mirror trimming.

Digital chemical etching is used to trim the output mirror thickness of wafer-fused VCSELs emitting at a wavelength near 1.5µm. The fine control of the photon cavity lifetime thus achieved is employed to extract important device parameters and optimize the combination of the threshold current, output power, and direct current modulation characteristics. The fabrication process is compatible with industrial production and should help in improving device yield and in reducing manufacturing costs.

Prethermalization of atoms due to photon-mediated long-range interactions.

Atoms can spontaneously form spatially ordered structures in optical resonators when they are transversally driven by lasers. This occurs when the laser intensity exceeds a threshold value and results from the mechanical forces on the atoms associated with superradiant scattering into the cavity mode. We treat the atomic motion semiclassically and show that, while the onset of spatial ordering depends on the intracavity-photon number, the stationary momentum distribution is a Gaussian function whose width is determined by the rate of photon losses. Above threshold, the dynamics is characterized by two time scales: after a violent relaxation, the system slowly reaches the stationary state over time scales exceeding the cavity lifetime by several orders of magnitude. In this transient regime the atomic momenta form non-Gaussian metastable distributions, which emerge from the interplay between the long-range dispersive and dissipative mechanical forces of light. We argue that the dynamics of self-organization of atoms in cavities offers a test bed for studying the statistical mechanics of long-range interacting systems.