Pumping Scheme Research Articles

Average-power (4.13 W) 59 fs mid-infrared pulses from a fluoride fiber laser system

We report a high-average-power mid-infrared ultrafast laser system consisting of a fluoride fiber mode-locked oscillator and a nonlinear amplifier. A backward pumping scheme was used in the amplifier to simultaneously realize pulse amplification and self-compression. The input signal polarization was demonstrated to play an important role in the self-compression process. Through the optimization of input polarization, a 4.13 W average-power 59 fs pulse at 2.8 µm was achieved, with an estimated pulse energy of 42.2 nJ and a peak power of 715 kW. To the best of our knowledge, this is the highest average-power pulse with sub-100-fs duration generated from a mid-infrared fiber laser system to date.

A Hybrid Self-Seeded Ti:sapphire Laser with a Pumping Scheme Based on Spectral Beam Combination of Continuous Wave Diode and Pulsed DPSS Lasers

A wide variety of applications require high peak laser intensity in conjunction with a narrow spectral linewidth. Typically, injection-locked amplifiers have been employed for this purpose, where a continuous wave oscillator is amplified in a secondary external resonant amplifier cavity using a pulsed pump laser. In contrast, here we demonstrate a setup that combines a CW Ti:sapphire oscillator and pulsed amplifier in a single optical cavity, resulting in a compact system. Dichroic beam combination of blue wavelength semiconductor diodes and the green wavelength of a Nd:YAG laser allowed the simultaneous excitation of the Ti:sapphire crystal by both continuous wave and pulsed pump sources. A linewidth of <2 MHz is achieved in continuous wave operation, while the linewidth increases to about 10 MHz in the combined CW+pulsed mode with a pulse duration of 73 ns. A peak pulse intensity of 0.2 kW is achieved, which should enable efficient single-pass second harmonic generation in a nonlinear crystal.

Exergoeconomic assessment of air separation units for pressurized O2 production incorporating two-phase expanders

Cryogenic air separation units (ASU) are the predominant method for delivering high-purity pressurized O2 at large capacities to relevant industrial processes. This study presents an exergoeconomic assessment of the integration of two-phase expanders (TPE) in two ASU configurations with (1) intermediate liquid oxygen pumping followed by gaseous O2 compression and (2) total liquid oxygen pumping to the delivery pressure. A comprehensive exergy analysis showed that TPE integration in the latter resulted in exergy efficiency increase of 1.1%-points and specific power consumption (SPC) reduction 15.5 kWh/ton (−4.4%), while for the former, the exergy efficiency increase amounted to 1.8%-points with 17.9 kWh/ton (−5.2%) lower SPC. A complete thermodynamic mapping for the different cases was presented. From an economic perspective, total liquid pumping reached levelized cost of oxygen reductions of 1.68 €/ton (−4.7%), while in the configuration with gas compressors it was limited to only 0.45 €/ton (−1.2%), relative to analogous ASU configurations with Joule-Thomson valve expansion. The total liquid pumping scheme with TPE presented a cost reduction of 4.3 €/ton (−11.2%) relative to the gaseous O2 compression counterpart. N2 by-product monetization can further improve the plant economic performance. Based on this assessment, integration of reliable TPE technology for incremental efficiency gains of pressurized O2 production in ASUs presents a promising opportunity to profitably contribute to energy efficiency and decarbonization goals.

Exceptional point singularities in multi-section DFB lasers

A laser exhibits both controllable gain and loss and, under proper design conditions, is an ideal non-Hermitian system allowing the direct observation and engineering of spectral singularities such as exceptional points (EPs). A dual section distributed feedback (DFB) quantum cascade laser (QCL) is a prototype of such a system, allowing the controlled coupling of a ladder of cavity Fabry–Perot modes to a quarter wave shifted DFB mode. Tuning the coupling strength and the gain difference between these two set of modes enables probing the regimes from weak coupling to strong coupling and the robust observation of EP singularities. At these EPs, the laser exhibits a sequence of lasing and switching off the coherent emission when pumped above transparency. Additionally, the pumping scheme allows the deliberate lifting of the EP degeneracy. These results show that dual section QCL is a perfect platform to study EPs because the coupling parameter and system loss can be tuned in a single device.

Automatic Control of the Hybrid Heat Pump for Heating of Multi-Storey Buildings

The work is devoted to control systems for hybrid heat pumps using the heat of return network water and outside air, designed to operate in district heating systems based on CHPP. The aim of the research is to develop control systems for heat pump operating on qualitative, quantitative and quantitative-qualitative heat schedules. The set goal is achieved by introducing two controlled heat exchangers: one of "refrigerant-water" type, installed after the evaporator and "refrigerant-air" type, installed after the gas cooler. The most important results are the hydraulic scheme of the heat pump, the control system scheme of gas superheater installed after the evaporator and gas supercooler installed after the gas cooler. The significance of the obtained results consists in obtaining a technical solution, which ensures the operation of the heat pump at different heating schedules. Equations of heat pump apparatuses have been obtained, in which the influence of flow rate and temperature of the working body on the heat pump operating mode is emphasized. The obtained heat balance equations allowed obtaining structures of automatic control systems for heat exchange apparatuses, compressors and controlling valves of the hybrid heat pump. The developed scheme of the heat pump air duct allowed using a minimum of heat of return network water in the heat pump. It has been established that the scheme of this automatic control system should include a functional converter linking the temperature of the outside air and the coordinates of the working body state at the outlet of the gas subcooler.

High-power and high-brightness Er:Yb codoped fiber MOPA operating at 1535 nm.

In this paper, we study the emerging 1535 nm Er: Yb codoped fiber MOPA with high power and high brightness. To characterize the interstage influence of this ASE-sensitive system, we conduct an interstage numerical model based on steady energy transfer model, where the seed and amplifier converge together. We analyze the amplifier setup, the seed pumping scheme, and feedback from inner reflection based on the model. Afterwards, we experimentally demonstrate a 1535 nm all fiber large mode area Er: Yb codoped fiber MOPA with the output power of 174.5 W, the brightness of 13.97 W/μm2sr, and ASE suppression ratio of 45 dB. To the best of our knowledge, this is the highest power and brightness of 1535 nm fiber lasers to date.

More than 5 kW counter tandem pumped fiber amplifier with near single-mode beam quality

We report on what we believe is the first demonstration of a monolithic counter tandem pumped ytterbium-doped fiber amplifier based on conventional double-clad fiber. At the maximum power of 5.03 kW, the amplifier delivered a near single-mode beam quality (M2 = 1.54), without stimulated Raman scattering effect or mode instability. In addition, we theoretically and experimentally investigated the impact of the 1080 nm signal laser from the amplifier on the 1018 nm fiber lasers used as pump sources. It revealed that even a small proportion of signal light coupled into a 1018 nm fiber laser cavity could cause a considerable power decline of the pump laser. Possible solutions to reduce the influence of signal light on pump sources were extensively discussed. Moreover, we experimentally confirmed the advantage in nonlinear effects mitigation of counter-pumping compared to co-pumping. This work proves the feasibility and superiority of the all-fiberized counter tandem pumping scheme, which could provide inspiration for future power scalability.

Collisional and radiative pumping in 22-GHz water masers

ABSTRACT We briefly discuss the history of pumping schemes for the common 22-GHz maser transition in o-H2O, and note that radiative mechanisms have been considered in the past, as well as the better known collisional pumping mechanisms associated with shock waves. Substantial IR irradiation is indeed destructive to inversion at 22-GHz under a wide range of physical conditions. We identify a small number of transitions, including 22 GHz, that can be pumped by both collisional and radiative schemes, and, through radiative transfer modelling over a grid of values in kinetic temperature, number density, and dust temperature, identify loci in density-kinetic temperature space where these schemes lead to strong inversions. The radiative pumping scheme generally operates at higher dust temperature, and lower kinetic temperature, than the collisional scheme. We identify a small network of transitions that form a radiative pumping scheme for the 22-GHz maser, involving radiative transitions of wavelength approximately 6 $\mu$m. This network is capable of supplying more than 50 per cent of the 22-GHz inversion under typical radiative pumping conditions, and it is consistent with the need for high dust and low kinetic temperatures determined from the modelling. We identify a probable case of radiative pumping in a massive star-forming region from the observation of a positive correlation between the flux densities of 22-GHz H2O masers and 6.7-GHz methanol masers. We discuss possibilities for finding radiatively pumped H2O maser lines in other source types.

Comparison between the dynamic characteristics of electric pump fed engine and expander cycle engine

A successful space launch mainly depends on the start-up process and variable operating conditions of rocket propulsion system. With the development of motor and battery technology, new electric pump is gradually used, in place of the traditional turbine pump, in rocket propulsion system. However, it is still unclear about the dynamic characteristics of the two processes in the two schemes (electric pump scheme and turbine pump scheme). In this research, simulation models of the basic components and overall system of an expander cycle hydrogen-oxygen engine were established on the basis of turbine pump and electric pump respectively. In the simulation models, the Centralized Parameter Method and the Stepwise Parameter Method are used for different components. The research results show that the power of hydrogen pump in the electric pump scheme is 25.5% lower than that in the turbine pump scheme, with speed and torque respectively 10.5% and 16.6% lower than those in the latter scheme. In the start-up process of the electric pump scheme, the flow of hydrogen pump underwent an overshoot of 3.7%, and the settling times of hydrogen and oxygen flows were both more than 40% shorter than those in the turbine pump scheme. Under variable operating conditions of turbine pump scheme, the speed of pump experienced an overshoot of about 20%, and the settling times of hydrogen and oxygen flows were 37% and 21% longer than those in the electric pump scheme. These findings are helpful to analyze the said two processes of expander cycle hydrogen-oxygen engine and further understand the difference in dynamic characteristics between the electric pump scheme and the turbine pump scheme.

Thermal modeling of resonantly pumped high power Tm-doped fiber amplifiers

A thermal model concerning resonantly pumped high power Tm-doped fiber amplifiers is established with temperature dependent parameters taken into consideration. With this model, performance of resonantly pumped Tm-doped fiber amplifiers at 1 kW output is investigated. Comparisons with the traditional 793 nm LD pump scheme shows that, resonant pumping, especially the 1.9 μm pump, is more favorable for high power Tm-doped fiber systems, featuring high operation efficiency with low heat load, limited temperature rise, controllable beam compression and a relatively small laser intensity at the output end. Besides, the power scalability of resonantly pumped Tm-doped fiber systems with 25/250 double-clad fiber is also explored numerically with various thermal effects, optical damage and nonlinear effects taken in account. Simulations show that, for 1 GHz narrow linewidth output, outer cladding damage and stimulated Brillouin scattering are the two primary limiting factors for power scaling. And, the maximal output of a Tm-doped fiber amplifier could reach 5.1 kW and 6.8 kW for 1.6 μm pump and 1.9 μm pump, respectively. For systems with broad spectrum, output approaching 10 kW can be expected.

Understanding the Impact of Spot Market Electricity Price on Wastewater Asset Management Strategy

Development of an advanced pumping control scheme is one of the useful methods that can be applied in operational optimisation of wastewater pumps. Optimisation of pumping control can benefit the utility by overall cost saving using different electricity pricing schemes from the energy market. As electricity prices can be varied based on the spot market in some countries such as Australia, the consideration of operating the pumps at the most favourable electricity price, when managed correctly, can offer remarkable savings. This paper provides understanding on the electricity spot price behaviour of South Australia in the National Electricity Market (NEM). Half-hourly electricity spot price data of over 22 years from January 1999 to June 2021 were analysed to investigate the key characteristics of spot prices, including seasonality (intraday, intraweek and seasonal price patterns), spiky behaviour and occurrences of negative prices. In addition, the possible impacts of other factors on electricity spot prices such as electricity demand and weather conditions on pump control were examined. Results indicate a strong relationship between electricity demand and spot price with the Pearson correlation coefficient up to R = 0.95, and extreme high spot prices tended to occur on scorching days with the maximum temperature above 35 °C when air-conditioner usage was high. This paper also explains the importance of electricity spot prices in the wastewater pump on/off operations and analyses opportunities for cost savings by including electricity spot price forecasts as an input of the smart controller to enhance the efficiency of the real-time pumping control.

Single-frequency Brillouin lasing based on a birefringent fiber Fabry–Pérot cavity

Stimulated Brillouin scattering (SBS) in a high-Q resonator is capable for narrow-linewidth laser generation for various applications but is limited by on-resonance pump to SBS matching from single-longitudinal lasing. In this Letter, we present a narrow linewidth laser via SBS that is enhanced in a monolithic high-Q fiber resonator. The unique cross-polarization pump scheme based on fiber birefringence prevents high-order SBS and ensures single-frequency Brillouin lasing with high intracavity conversion efficiency. Fundamental linewidth of 50 Hz is achieved. Moreover, our scheme also allows precise characterization of Brillouin frequency shift and gain bandwidth of some nonlinear materials.

Optimization Control of Oilfield Waterflooding Systems Based on Different Zone and Pressure

The scrapping of old waterflooding wells and the increase in new waterflooding wells results in mixed flooding of high–low pressure wells in various oil layers in waterflooding systems. In order to meet production operation requirements, the whole system is in a state of high pressure, which leads to an increase in energy consumption and complicates the operation of waterflooding networks. According to the pressure distribution of wells, proceeding with regional accurate waterflooding can reduce operation costs and improve development efficiency. Considering the technical constraints of waterflooding networks, a method was proposed, which can quantitatively optimize classification and zoning for waterflooding of high–low pressure wells according to the pressure of networks and wells. At the same time, the ant colony algorithm and genetic algorithm were fused to form a new adaptive ant colony genetic hybrid algorithm, which can effectively determine the best pumping scheme of the waterflooding station, the pumping flow and optimize the low-pressure area. The K-means algorithm was used to optimize the topology of the pipe network in the high-pressure area to reduce the overall waterflooding pressure. Finally, the method was successfully applied to the large-scale waterflooding system including 2200 wells and 10 waterflooding stations in sites in China. The results show that the method is effective for the operation and reconstruction of waterflooding pipe networks with large-scale and serious mixed high–low pressure.

Gain Clamped Bi-Doped Fiber Amplifier With 150 nm Bandwidth for O- and E-Bands

Global data traffic is continuously growing year by year. In this regard, telecom companies faced the problem of increasing data transmission rate, which is becoming more and more challenging. One of options that could help to increase optical links capacity is an expansion of the spectral range of DWDM systems used in telecom by inclusion of the O-band and/or the E-band. An ability to engage these spectral ranges directly related to the presence of suitable effective optical amplifiers. In this work, we studied different modifications of Bi-doped fiber amplifier operating in the O- and E-bands in order to obtain the widest gain spectrum in a single device. In particular, one- and two-wavelength pumping and gain-clamped schemes, as well as usage of a Bi:P<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula>O<inline-formula><tex-math notation="LaTeX">$_\text {5}$</tex-math></inline-formula>-SiO<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula> and Bi:GeO<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula>-SiO<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula> fibers combination, were considered. As a result, an amplifier with 150 nm &#x2013;6 dB bandwidth, <inline-formula><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula>25 dB peak gain operating in the range from <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>1300 to <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>1450 nm was developed. To achieve the highest spectral width, we compare a gain-clamped at 1280 nm cavity pumped at 1180 nm with dual pump scheme at 1180 nm and 1270 nm along with a combination of active media composed of Bi:P<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula>O<inline-formula><tex-math notation="LaTeX">$_\text {5}$</tex-math></inline-formula>-SiO<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula> and Bi:GeO<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula>-SiO<inline-formula><tex-math notation="LaTeX">$_\text {2}$</tex-math></inline-formula> fibers.

Continuous multi-step pumping of the optical clock transition in alkaline-earth atoms with minimal perturbation.

A suitable scheme to continuously create inversion on an optical clock transition with negligible perturbation is a key missing ingredient required to build an active optical atomic clock. Repumping of the atoms on the narrow transition typically needs several pump lasers in a multi step process involving several auxiliary levels. In general this creates large effective level shifts and a line broadening, strongly limiting clock accuracy. Here we present an extensive theoretical study for a realistic multi-level implementation in search of parameter regimes where a sufficient inversion can be achieved with minimal perturbations. Fortunately we are able to identify a useful operating regime, where the frequency shifts remain small and controllable, only weakly perturbing the clock transition for useful pumping rates. For practical estimates of the corresponding clock performance, we introduce a straightforward mapping of the multilevel pump scheme to an effective energy shift and broadening of parameters for the reduced two-level laser model system. This allows us to evaluate the resulting laser power and spectrum using well-known methods.

Conceptual Modelling of Two Large-Scale Mine Water Geothermal Energy Schemes: Felling, Gateshead, UK.

A conceptual model is presented of two MW-scale low enthalpy mine water geothermal heat pump schemes that are being developed in Tyneside, UK. The Abbotsford Road scheme (54.955° N 1.556° W) is operating (as of May 2021) at 20–30 L/s, abstracting groundwater (and heat) from an unmined Coal Measures Upper Aquifer System (UAS) and reinjecting to the deeper High Main Aquifer System (HMAS), associated with the High Main (E) coal workings and the overlying High Main Post sandstone. A similar scheme, 700 m away at Nest Road (54.959° N 1.564° W), abstracts at 40 L/s from the HMAS, recovers heat from the mine water and reinjects the thermally spent water to deeper workings associated with the Hutton (L), Harvey-Beaumont (N) (and possibly other) coal seams, termed the Deep Mined Aquifer System (DMAS). The three aquifer systems are vertically discontinuous and possess different hydraulic (storage, transmissivity and continuity) properties that would have been near-impossible to predict in advance of drilling. At the sites, 10 boreholes were drilled to obtain five usable production/reinjection boreholes. Development of mine water geothermal energy schemes thus carries a significant project risk, and also a potential ongoing maintenance burden related to iron hydroxide scaling. These do not preclude mine water geothermal as a useful low carbon heating and cooling technology, but the involvement of skilled hydrogeologists, hydrochemists, mining and groundwater engineers is a pre-requisite.

High sensitivity pH sensing by using a ring resonator laser integrated into a microfluidic chip.

We present a chip-scale integrated pH sensor with high sensitivity by using an optofluidic ring resonator (OFRR) laser. An optical fiber with a high refractive index (RI) is employed both as an optical cavity and the sensing reactor along a microchannel, while disodium fluorescein (DSF) aqueous solution with a low RI is served as the cladding gain medium and fluorescent probes. The pump light is introduced along the fiber axis and guided by the total internal reflection at the fiber/cladding interface. The evanescent field of the pump light extends out of the fiber surface and efficiently excites the dye molecules residing in the evanescent field region of the Whispering Gallery Modes (WGMs) of the OFRRs to produce lasing emission. This pumping scheme provides a uniform excitation to the gain medium and significantly increases the signal-to-noise ratio, ensuring a low lasing threshold and highly sensitive sensing. The lasing threshold property under different pH conditions is experimentally and theoretically conducted to evaluate the sensing performance, which shows that the lasing threshold highly depends on the pH value of the cladding solution due to the increasing deprotonation process. We further verify that the intensity of the lasing emission and the pH value shows good linearity in the pH range 6.51-8.13, with a 2-order-of-magnitude sensitivity enhancement compared to fluorescence measurement. The proposed OFRR lasing platform shows excellent robustness and low sample consumption, providing a powerful sensing strategy in medicine, and hazardous/toxic/volatile sensing, which require label-free, real-time, and in situ detection.

Upconversion and near infrared emission in Yb–Tm mediated by ZnTe crystals in oxide glasses

This work presents a detailed investigation of the blue and near infrared (NIR) emission of Tm3+ and Yb3+ ions in ZnTe doped oxide glasses. Absorption, luminescence and lifetime measurements were performed in order to optimize the luminescent properties of Yb3+ and Tm3+. The influence of ZnTe and Yb3+ concentration on the enhancement and quenching of the emissions at 470 nm and 980 nm were determined. It was observed that the Yb3+ luminescence increases by a factor of 10, while the Tm3+ blue emission at 470 nm is quenched for both the presence of Yb3+ and ZnTe. The enhancement in the Yb3+ emission is attributed to the presence of ZnTe. Moreover, it is demonstrated that the glass can be pumped with additional wavelengths (325 nm and 532 nm) due to the absorption from the ZnTe semiconductor, allowing alternative pumping schemes. Calculations of the energy transfer microparameters from Yb3+-Yb3+ and Yb3+-Tm3+ were also performed, evaluating the influence of ZnTe in the process.

2.1 μm, 1.52 μJ square-wave noise-like pulse from an all-fiber figure-of-9 Ho-doped oscillator and single-stage amplifier.

A 2.1 μm, high energy square-wave noise-like pulse (NLP) in an all-fiber Ho-doped fiber laser is proposed, which consists of an oscillator and a single-stage amplifier. In the figure-of-9 oscillator, mode-locking is achieved based on the nonlinear amplifying loop mirror, employing a long gain fiber to provide sufficient gain in 2.1 μm band and optimizing the cavity length to obtain maximum pulse energy output. With appropriate pump power and polarization state, the oscillator emits a 175.1 nJ square-wave NLP with center wavelength of 2102.2 nm and spike width of 540 fs. The 3-dB spectral width and pulse envelope width are 11.2 nm and 6.95 ns, respectively. The single-stage amplifier employs a bi-directional pump scheme. After amplification, 5.8 W NLP with a slope efficiency of 56.8% is obtained. The pulse energy of NLP is scaled to 1.52 μJ, which is the highest pulse energy of NLP at 2.1 μm to the best of our knowledge. The obtained high-energy square-wave NLP-fiber laser has great potential in mid-infrared laser generation.

Optical Thouless pumping transport and nonlinear switching in a topological low-dimensional discrete nematic liquid crystal array

We theoretically investigate a Thouless pumping scheme in the 1D topological Su-Schrieffer-Heeger (SSH) model for single and multiple band-gaps systems when implemented in a discrete nematic liquid crystal arrangement. For an electrically controlled SSH waveguide array, we numerically demonstrate edge-to-edge light transport at low power levels. On the other hand, at higher powers, the transport is frustrated by light-induced nonlinear defect states, giving rise to robust all-optical switching.