Synchronous Pumping Research Articles

Fiber-based optical parametric oscillator with flexible repetition rates by rational harmonic pumping.

We demonstrated a fiber-based synchronously pumped optical parametric oscillator (SPOPO) with flexible repetition rates while retaining the cavity length. In contrast to conventional free-space SPOPO, the repetition rate of output signal pulses was solely determined by the repetition rate of the pump source in harmonic, fractional and rational operations. The relevant mechanism relies on synchronous pumping and intrinsic losses in our fiber resonator. The novel scheme enabled us to flexibly tune the repetition rate from 0.5 to 6.0 MHz without altering the resonator configuration. The resulting pulse properties were systematically analyzed at various operation conditions, and particularly showed that a wavelength tuning range of 157 nm was obtained. Such rational harmonic resonance implemented in our SPOPO provides not only a simple yet effective way to tune the repetition rate, but also a feasible approach to narrow down the spectral bandwidth. The presented SPOPO could be useful in nonlinear biomedical imaging by offering a convenient approach to optimize the pulse repetition rate for different biomedical samples with minimum photodamage.

In Situ Calibration of Magnetic Coil System Using Ellipticity-Induced Bell-Bloom Magnetometer

The three-axis coil system is most commonly used in magnetic field measurement. The coil constant is an important parameter. We demonstrate a method to measure the coil constant based on the Larmor frequency. An elliptically polarized light is used to simultaneously excite the spin orientation and spin alignment via synchronous optical pumping. And then the coil system can be calibrated by measuring the magnetic resonance frequency of Bell-Bloom magnetometer. The advantage of this method is that the coil constants of all three directions can be obtained without any active adjustments. It is important for some applications, such as measuring the biological magnetic field with the integrated magnetometer. The method for calibration of a three-axis coil system is experimentally exploited. The experimental results show that the calibration accuracy of pT level can be achieved.

Mathematical model of a drive system with synchronous motors and vertical pumps

The paper presents a mathematical model of an electrical load node consisting of a power transformer and synchronous motors which rotate vertical pumps using non-rigid transmission. Modified principle of Hamilton–Ostrogradsky served as the basis for construction of the model. Using the developed mathematical model of the node, electromechanical transients in the object are studied. The resultant system of dynamic state nonlinear differential equations is introduced in the normal Cauchy’s form. Computer simulation findings are displayed by means of figures; they are under ongoing analysis.

Raman-converted high-energy double-scale pulses at 1270 nm in P2O5-doped silica fiber.

This work presents implementation of a new approach to single-cascade Raman conversion of laser pulses from the spectral range around 1.1 µm into the 1.3-µm wavelength region. The proposed conversion technique relies on double-scale pico-femtosecond pulses for synchronous pumping of an external cavity made of phosphosilicate fiber with high-precision adjustment of pulse repetition rate to the inter-mode frequency of the external cavity. This enabled generation of double-scale pulses centered at 1270 nm featuring a record energy of 63 nJ and the pulse envelope duration of 88-180 ps with the sub-pulse duration of 200 fs. The fraction of the radiation that was converted into the 1270 nm range amounted to 47 percent of the total Raman-converted radiation power. The generated results offer promising possibilities for new spectral ranges to be developed in the field of high-energy pulsed sources with unique double-scale temporal structure.

Measurement of the Ratio between g‐Factors of the Ground States of 87Rb and 85Rb

AbstractThe ratio between the Landé g‐factors of the Rb and Rb ground‐state hyperfine levels is experimentally measured to be , consistent with previous measurements. The g‐factor ratio is determined by comparing the Larmor frequencies of overlapping ensembles of Rb and Rb atoms contained within an evacuated, antirelaxation‐coated vapor cell. The atomic spins are polarized via synchronous optical pumping and the Larmor frequencies are measured by off‐resonant probing using optical rotation of linearly polarized light. The accuracy of this measurement of exceeds that of previous measurements by a factor of ≈50 and is sensitive to effects related to quantum electrodynamics.

SOA fiber laser mode-locked by gain modulation

This work reports, for the first time to our knowledge, on an experimental and theoretical study of mode locking via synchronous pumping of a semiconductor optical amplifier (SOA) used as the active medium of a fiber laser. SOA modulation with injection current pulses having duration of 1.2 μs and repetition rate equal to that of the fundamental intermode frequency spacing of the cavity (84.9 kHz) led to generation of mode-locked pulses with duration of 650 ns at a wavelength of 1.54 μm. The feasibility of the proposed method and the basic parameters of the generated pulses are corroborated by numerical modeling. The key advantages of the proposed laser are simplicity of implementation, comparatively high efficiency, spectral universality, and possibility of pulse shape control.

Threshold decrease in intracavity optical parametric oscillator synchronously pumped by mode-locked laser

An intracavity optical parametric oscillator (IOPO) pumped by a continuous-wave (CW) mode-locked laser is experimentally realized. The fundamental cavity and optical parametric oscillator cavity are designed to satisfy synchronous pumping. The output characteristics of signal and idle light are measured. Because of higher fundamental photon intensity in IOPO, the threshold of IOPO is lower than that of an extra-cavity optical parametric oscillator. The spectroscopy of signal light is obtained and the wavelength of idle light can be estimated to be 3.298 μm from noncritical phase matching. Based on the intensity fluctuation mechanism of fundamental locking, the dynamical model for IOPO pumped by a CW mode-locked laser is developed. The simulated results for the temporal shape of three lights are calculated from the derived rate equations. Because of dispersion, the signal pulse width of the theory is smaller than that of the experiment with the same pump energy.

Highly efficient picosecond all-solid-state Raman laser at 1179 and 1227 nm on single and combined Raman lines in a BaWO4 crystal

We present a highly efficient ring-cavity all-solid-state BaWO4 Raman laser generating at both the long-shift (ν1=925 cm-1) and short-shift (ν2=332 cm-1) Raman lines under external picosecond synchronous pumping at the wavelength of 1063nm. Very high slope efficiencies and output pulse energies of 68.8% and 103nJ at the ν1-shifted Stokes wavelength of 1179nm, and 38.6% and 53nJ at the (ν1+ν2)-shifted Stokes wavelength of 1227nm have been achieved. Self-mode locking of the (ν1+ν2)-shifted Stokes field under intracavity pumping by the ν1-shifted Stokes field allowed to realize 12-fold shortening of the 1227nm radiation pulse down to 3ps close to the shorter dephasing time of the ν2 Raman line at the output pulse peak power 1.5 times higher than the pump peak power.

Cavity length matching and optical resonances in a Raman laser with the multimode pump source.

We report on the observation of local reduction in generation threshold and enhancement in the output energy of a nanosecond Raman laser when the round-trip time of its cavity is matched with that of a longitudinally multimode pump laser or related to the latter as a ratio of small integers. We refer both observations to the synchronous pump effect originating from the periodicity in the small-scale intensity structure of the pump pulse.

In situ measurement of light polarization with ellipticity-induced nonlinear magneto-optical rotation

A precise, accurate, and relatively straightforward in-situ method to measure and control the ellipticity of light resonantly interacting with an atomic vapor is described. The technique can be used to minimize vector light shifts. The method involves measurement of ellipticity-induced resonances in the magnetic-field dependence of nonlinear magneto-optical rotation of frequency-modulated light. The light propagation direction is orthogonal to the applied magnetic field $\textbf{B}$ and the major axis of the light polarization ellipse is along $\textbf{B}$. When the light modulation frequency matches the Larmor frequency, elliptically polarized light produces precessing atomic spin orientation transverse to $\textbf{B}$ via synchronous optical pumping. The precessing spin orientation causes optical rotation oscillating at the Larmor frequency by modulating the atomic vapor's circular birefringence. Based on this technique's precision, in-situ nature (which avoids systematic errors arising from optical interfaces), and independent control of the most important systematic errors, it is shown that the accuracy of light ellipticity measurements achievable with this technique can exceed that of existing methods by orders of magnitude.

2 μm Raman fiber laser based on a multimaterial chalcogenide microwire

We report a Raman fiber laser based on a multimaterial chalcogenide microwire. The microwire structure comprises a core of As38Se62, a cladding of As38S62, and a coating of poly-methyl methacrylate. The microwire is a robust, high confinement waveguide compatible with the mid-infrared. With the microwire inserted in a ring cavity, Raman laser oscillation at a wavelength of 2.025 μm occurs from synchronous pumping at a wavelength of 1.938 μm. The input peak power required to reach threshold is 4.6 W and the power slope efficiency is 4.5%. Numerical simulations are in good agreement with experimental results and predict chirp-free femtosecond pulses.

Performance enhancement of the synchronous micropump based on experimental and numerical investigations of the magnetic field flux density in planar microcoils

This study presents numerical and experimental investigations targeting enhancing the magnetic field flux magnitudes in electroplated copper microcoils. Improved designs are used in the development of a new generation of the electromagnetic-based synchronous micropump in order to enhance its performance (i.e. the maximum achievable output pressure and flow rate). The synchronous micropump concept is based on managing the movement of two magnets in an annular fluidic channel. The magnets’ rotation is achieved by sequentially activating a set of three-dimensional microcoils to repel or attract one magnet (travelling piston) through the channel, whereas the second one is anchored between the inlet and the outlet ports (valve piston). At the end of each pumping cycle, the magnets exchange their functions. To achieve the maximum achievable output pressure and flow rate, higher magnetic fields without exceeding the material temperature limitation are required. The stronger the magnetic fields that can be generated, the higher the hydraulic power that the pump can deliver. The microcoil conductor width and height were optimized to generate higher magnetic field flux intensity within the pump limitation parameters (i.e. pump footprint and coils’ maximum heat dissipation limit). The new generation of the synchronous pump was run at a rotational speed of up to 800 rpm and provided a maximum flow rate of 3.56 ml/min and a maximum pressure head of 687 Pa.

Compact KGd(WO4)2 picosecond pulse-train synchronously pumped broadband Raman laser.

We demonstrate an efficient approach to realizing an extra-cavity, synchronously pumped, stimulated Raman cascaded process under low repetition frequency (1 kHz) pump conditions. We also construct a compact KGd(WO4)2 (KGW) crystal picosecond Raman laser that has been configured as the developed method. A pulse-train green laser pumped the corresponding 70 mm long KGW crystal Raman cavity. The pulse train contains six pulses, about 800 ps separated, for every millisecond; thus, it can realize synchronous pumping between pump pulse and the pumped Raman cavity. The investigated system produced a collinear Raman laser output that includes six laser lines covering the 532 to 800 nm spectra. This is the first report on an all-solid-state, high-average-power picosecond collinear multi-wavelength (more than three laser components) laser to our knowledge. This method has never been reported on before in the synchronously pumped stimulated Raman scattering (SRS) realm.

Optical parametric oscillator of mid-IR, visible and UV ranges with synchronous pumping by a -switched mode-locked Nd : YAG laser

The parametric generation in a nonlinear PPLN crystal synchronously pumped by a -switched mode-locked Nd : YAG laser with a pulse duration of is studied. The output pump intensity in the nonlinear crystal reaches . At a pulse repetition rate of , the average output power at the idler wavelength is , the peak power is , and the conversion efficiency (with respect to the absorbed power) is . The radiation linewidth at the signal wavelength is . Along with the signal and idler waves, the output emission spectrum contains lines at wavelengths of 822, 754, 624, 532, 463, 442, 392 and . The tunable radiation with wavelengths in the vicinity of 392, 463 and is observed for the first time. The tuning ranges for the new lines are measured and their origin is explained.

Network Scale Modeling of Lymph Transport and Its Effective Pumping Parameters.

The lymphatic system is an open-ended network of vessels that run in parallel to the blood circulation system. These vessels are present in almost all of the tissues of the body to remove excess fluid. Similar to blood vessels, lymphatic vessels are found in branched arrangements. Due to the complexity of experiments on lymphatic networks and the difficulty to control the important functional parameters in these setups, computational modeling becomes an effective and essential means of understanding lymphatic network pumping dynamics. Here we aimed to determine the effect of pumping coordination in branched network structures on the regulation of lymph flow. Lymphatic vessel networks were created by building upon our previous lumped-parameter model of lymphangions in series. In our network model, each vessel is itself divided into multiple lymphangions by lymphatic valves that help maintain forward flow. Vessel junctions are modeled by equating the pressures and balancing mass flows. Our results demonstrated that a 1.5 s rest-period between contractions optimizes the flow rate. A time delay between contractions of lymphangions at the junction of branches provided an advantage over synchronous pumping, but additional time delays within individual vessels only increased the flow rate for adverse pressure differences greater than 10.5 cmH2O. Additionally, we quantified the pumping capability of the system under increasing levels of steady transmural pressure and outflow pressure for different network sizes. We observed that peak flow rates normally occurred under transmural pressures between 2 to 4 cmH2O (for multiple pressure differences and network sizes). Networks with 10 lymphangions per vessel had the highest pumping capability under a wide range of adverse pressure differences. For favorable pressure differences, pumping was more efficient with fewer lymphangions. These findings are valuable for translating experimental measurements from the single lymphangion level to tissue and organ scales.

Synchronous Spin-Exchange Optical Pumping.

We demonstrate a new approach to precision NMR with hyperpolarized gases designed to mitigate NMR shifts due to the alkali spin-exchange field. The NMR bias field is implemented as a sequence of alkali (Rb) 2π pulses, allowing the Rb polarization to be optically pumped transverse to the bias field. When the Rb polarization is modulated at the noble-gas (Xe) NMR resonance, spin-exchange collisions buildup a precessing transverse Xe polarization. We study and mitigate novel NMR broadening effects due to the oscillating spin-exchange field. Spin-exchange frequency shifts are suppressed 2500×, and Rb magnetometer gain measurements project photon shot-noise limited NMR frequency uncertainties below 10 nHz/sqrt[Hz].

Rebuilding After a Disaster: Turning a Bad Situation into an Opportunity to Make Electrical Safety Improvements

In February 2011, construction had just begun on a planned electrical safety improvement project at the East Bay Municipal Utility District's (EBMUD's) Walnut Creek raw water pumping plants (WCPPs 1 and 2) when the electrical substation powering the facility was destroyed by a fault. This was followed a month later by a flood that completely filled the building that houses WCPPs 1 and 2, submerging six large synchronous motors, pumps, and related electrical distribution equipment. These nearly simultaneous catastrophic events dramatically expanded and redefined the scope of the planned work. An immediate priority was to rebuild the electrical substation within 12 months so that the district could restore power to the undamaged WCPP 3 to meet the anticipated summer pumping demands. A longer-term priority was to completely rebuild the pumps and motors and replace the station service motor control centers (MCCs); switchgear lineups; controls; and the heating, ventilation, and air conditioning system at WCPPs 1 and 2 within the next 24 months. This article presents how these two incidents occurred and discusses how they were turned into an enhanced safety design opportunity.

FWM Dynamics Under Dual-Pump Thermal Behavior in Silicon Microring Resonator

The silicon microring resonator is a superb platform for both fundamental studies and practical applications of various nonlinear optic phenomena. However, the highly enhanced light intensity in the ring cavity makes it quite sensitive to thermal variations and can in turn incur detrimental instability or degradation to the concurrent nonlinear processes. Here, we revisit the four-wave mixing effect in a silicon microring resonator by characterizing the detailed parametric dynamics under the influence of a dual-pump thermal behavior of the microring. We compare different pump scanning schemes and show that thermal variations of cavity modes can greatly impact the operation condition and efficiency of four-wave mixing. A synchronous pump scanning method is proposed and demonstrated to be the most applicable scheme to achieve high-efficiency parametric energy conversion in a thermally sensitive microring resonator.

Subharmonic synchronously intracavity pumped picosecond optical parametric oscillator for intracavity phase interferometry

The laser system suitable for precise intracavity phase interferometry is presented. The system is based on an intracavity pumped PPLN linear optical parametrical oscillator (OPO). For synchronous pumping of OPO a SESAM-mode-locked, picosecond, diode-pumped Nd:YVO4 linear oscillator, operating at 1.06 µm was used. The OPO cavity was set to be twice as long as the pumping Nd:YVO4 laser cavity. The pumping laser was set in such a manner that the parametric gain inside the PPLN overcame the OPO threshold only for one direction of pumping pulse propagation. This leads to the generation of two independent trains of pulses at the 1.5 µm spectral range. To verify the system performance, a LiNbO3 electro-optic phase modulator was placed inside the OPO. The RF-signal derived from the pumping pulse train, detected by a fast photodiode and divided by two, was applied on the modulator. A stable beat-note signal between the two OPO trains was successfully measured for the first time from such a compact, all-diode-pumped laser system. For RF-signal amplitude from 100 up to 700 mV beat-note frequency varied from 232 up to 1847 Hz which corresponded to detected phase-shift 36–250 µrad. The bandwidth of beat-note was less than 1 Hz (FWHM) resulting in phase-shift measurement error 1.5 × 10−7 rad.

Rotary pump speed modulation for generating pulsatile flow and phasic left ventricular volume unloading in a bovine model of chronic ischemic heart failure

Rotary blood pumps operate at a constant speed (rpm) that diminishes vascular pulsatility and variation in ventricular end-systolic and end-diastolic volumes, which may contribute to adverse events, including aortic insufficiency and gastrointestinal bleeding. In this study, pump speed modulation algorithms for generating pulsatility and variation in ventricular end-systolic and end-diastolic volumes were investigated in an ischemic heart failure (IHF) bovine model (n = 10) using a clinically implanted centrifugal-flow left ventricular assist device (LVAD). Hemodynamic and hematologic measurements were recorded during IHF baseline, constant pumps speeds, and asynchronous (19-60 cycles/min) and synchronous (copulse and counterpulse) pump speed modulation profiles using low relative pulse speed (±25%) of 3,200 ± 800 rpm and high relative pulse speed (±38%) of 2,900 ± 1,100 rpm. End-organ perfusion, hemodynamics, and pump parameters were measured to characterize pulsatility, myocardial workload, and LVAD performance for each speed modulation profile. Speed modulation profiles augmented aortic pulse pressure, surplus hemodynamic energy, and end-organ perfusion (p < 0.01) compared with operation at constant speed. Left ventricular external work and myocardial oxygen consumption were significantly reduced compared with IHF baseline (p < 0.01) but at the expense of higher LVAD power consumption. Pump speed modulation increases pulsatility and improves cardiac function and end-organ perfusion, but the asynchronous mode provides the technologic advantage of sensorless control. Investigation of asynchronous pump speed modulation during long-term support is warranted to test the hypothesis that operating an LVAD with speed modulation will minimize adverse events in patients supported by an LVAD that may be associated with long-term operation at a constant pump speed.