Pump Power Research Articles

MAXIMUM BENEFITS FROM THE USE OF T-SHAPED TREE FLOW GEOMETRY WITH RECTANGULAR SHAPE OF THE CHANNELS: PERFORMANCE EVALUATION

The study defines the conditions and constraints that must be obeyed to obtain the maximum benefit from using a heat exchanger with a T-shaped tree flow configuration and rectangular shape of the channels. The flow is laminar and fully developed with constant physical properties. The boundary condition is the fixed temperature of the channel wall. The variation of the heat flow ratio and augmentation entropy generation number Nsa with the dimensionless mass flow rate, shape factor ratio, and complexity have been investigated. Comparisons of the thermal performance with other heat exchanger configurations like serpentine for two cases have been made. The requirement for Nsa <=1 has been implemented as a constraint instead of one of fixed pumping power. The performance evaluation criterion has been introduced as a general criterion to define the most beneficial complexity and working parameters.

Numerical computations on thermal performance of large-scale Ti-Mn-based metal hydride storage reactor via open source CFD software

Certain metals and metal alloys can absorb hydrogen through an exothermic chemical reaction, resulting in the formation of metal hydrides. To maintain a rapid charging rate, the produced heat must be extracted as rapidly as it is generated. This study was attempted to evaluate the heat transfer enhancement in a cylindrical hydrogen storage reactor equipped with a central tube for large-scale applications using a 3D transient model. Finite-volume simulations are carried out using the open-source software package OpenFOAM to systematically investigate the impacts of material thermophysical properties, cooling media, and heat exchanger design on the heat transfer behaviors and hydrogen storage rate. The reactor’s performance was evaluated in terms of temperature and total hydrogen mass history profiles, in addition to pressure drop. The findings indicated that the charging time was improved by roughly 86%, compared to the case without thermal enhancement to attain 90% hydrogen storage capacity. A diminished pressure drop was observed between the water-based Al2O3 nanofluid with 5 vol% concentration and pure water at lowered coolant flow velocities, hence enhancing pumping power efficiency. Moreover, the results demonstrated that the storage rate is markedly improved by enhancing the effective thermal conductivity of the hydride bed, increasing the heat exchange area, accelerating the coolant flow rate, and lowering its temperature. The outcomes highlighted the possibility of advancing the current metal hydride reactor for practical application.

Compression stability enhancement with low temperature-dependent SBS compressors at high repetition rates

The stimulated Brillouin scattering (SBS) pulse compression with stable compression efficiency in low temperature-dependent SBS compressors is demonstrated by suppressing the rising edge broadening under high repetition rates. Theoretical analysis reveals that the difficulty in achieving stable SBS compression is caused by the broadening of the phonon lifetime owing to thermal effect, and this undesirable fluctuation can be effectively suppressed by a low temperature-dependent medium. Reductions of 66.33% on Stokes pulse width broadening and 50% on rising time with repetition rate were achieved under 36.87% enhancement of kinematic viscosity stability. Benefiting from a stable gain coefficient, the maximum fluctuation of 3.51% in transient Stokes pulse energy was demonstrated at maximum pump power with stability enhancement of 16.28% on steady-state energy reflectivity.

High-power 1176 nm vortex beam generated in a Nd:YVO4 self-Raman laser via annular pumping

Abstract Optical vortices carrying orbital angular momentum are of marked importance for a myriad of practical applications. We demonstrate the direct generation of high-power (watt-level) Laguerre–Gaussian vortex beam (LG01 with radial index p = 0 and azimuthal index l = 1) in a continuous-wave Nd:YVO4 self-Raman laser at 1176 nm with annular pumping by an axicon. Under an absorbed pump power of 17.17 W, a maximum vortex Raman output of 1.43 W was achieved with an optical conversion efficiency of 8.3%. The Stokes output beam has a stable helical wavefront with well-determined handedness at high pump power. Furthermore, selective generation of LG01 modes with opposite handedness can be realized simply by breaking azimuthal symmetry by tilting the output coupler. The results show that the annular pumping by an axicon has great potential in the development of compact Raman vortex laser systems with high power, high beam quality and versatile laser wavelengths.

A 30 mW Laser Oscillator at 2.72 μm and 2.8 μm Wavelengths Based on Er3+-Doped Tungsten–Tellurite Fibers

The purpose of this paper was to develop fiber lasers in the 2.7–2.8 μm range based on the tungsten–tellurite glass fiber that is technically robust compared to the other fibers currently used in laser engineering. Using an advanced technology for producing ultra-dry tellurite glasses, we manufactured Er3+-doped tungsten–tellurite glass preforms with extremely low absorption and obtained active single-mode tungsten–tellurite fibers. Based on a 70 cm long fiber, we developed a laser oscillator pumped by a low-cost, high-efficiency diode laser at 976 nm. At the highest used pump power, the laser output reached 33 mW, which may be interesting for practical applications. We also measured the single-pass on/off gain of the fibers and showed that with increasing pump power amplification, as high as 5 can be reached, showing that such active fibers may also be used for increasing laser output.

Diamond guide star laser pulsed at a Larmor frequency

We demonstrate a diamond sodium guide star laser pulsed at a Larmor repetition rate of 350 kHz. The single-frequency 589 nm laser reaches an average output power of 32.6 W with 75.6 W pump power in a duty cycle of 19%. Significant improvement in the intensity fluctuations is observed in the conversion from the pump to the frequency-doubled laser. Temporal behaviors and instant photon conversion of laser fields are also investigated in the experiment. This laser system offers a promising approach to address the need for a high-performance sodium guide star laser source, which is crucial for the advancement of applications in terrestrial astronomy and space-situational awareness.

Effect of Evaporation and Condensation Temperature on Performance of Organic Rankine System Using R134a, R417A, R422D, R245fa

Organic Rankine Cycles (ORCs) are identified as one of the most promising technologies for generating electricity from low-grade heat sources. Unlike conventional Rankine cycles, ORCs operate at lower temperatures and pressures. This allows them to utilize organic fluids or refrigerants as the working fluid instead of water, which is better suited for high-pressure and high-temperature applications. The performance and design of an ORC system are heavily dependent on the chosen working fluid. Therefore, selecting the right working fluid is crucial for a specific application, such as solar thermal, geothermal, or waste heat recovery. This study analyzed the performance of ORCs using four different working fluids: R-134a, R-245fa, R417A, and R422D. The researchers investigated how variations in condensation and evaporation temperatures affect thermal efficiency, mass flow rate, pump power, and turbine pressure ratio. The Engineering Equation Solver (EES) program was used for analyses. The results demonstrated that condensation and evaporation temperatures significantly influence system performance. The study found that ORC systems using R417A and R422D exhibited higher efficiencies compared to the other working fluids analyzed. Additionally, these fluids required lower mass flow rates per unit of power generation compared to the other fluids.

B-AsP as the saturable absorber for a mid-infrared 3 µm nanosecond laser

Black arsenic-phosphorus (B-AsP) has better stability than traditional black phosphorus (BP), and it was utilized to modulate a mid-infrared (mid-IR) 3 µm laser for what we believe to be the first time. The linear and nonlinear absorption characteristics of B-AsP at 3 µm were also investigated. The maximum continuous wave (CW) output power of the Er: SrF2 laser was 240 mW with an absorbed pump power of 2.87 W, resulting in a corresponding slope efficiency of 8.1%. During passively Q-switched (PQS) experiments, a laser pulse with a minimum duration of 188 ns was successfully generated at a repetition rate of 78 kHz, and the relevant single-pulse energy was 2.0 µJ. To the best of our knowledge, this is the narrowest passively Q-switched pulse for Er:SrF2 crystal laser. Our results indicate that B-AsP SA was a promising candidate to be the optical modulator in the mid-IR wavelength range.

LD-Pumped 228 nm Nd:GdVO4/Cr4+:YAG Passively Q-Switched Solid-State Laser

The 228 nm deep ultraviolet laser, leveraging its advantages of short wavelength, high photon energy, and low thermal effect, can significantly enhance the Raman signal in resonance Raman spectroscopy and demonstrates broad application potential in areas such as precision processing of photonic devices. This paper investigates a solid-state linear-cavity passively Q-switched 228 nm deep ultraviolet laser. Firstly, the laser employs an Nd:GdVO4 crystal as the gain medium, combined with Cr4+:YAG crystal passive Q-switching technology to generate 912 nm pulsed fundamental frequency light. Subsequently, a lithium metaborate (LBO) crystal is used to generate 456 nm second-harmonic light, and finally, a barium metaborate (BBO) crystal is utilized to achieve 228 nm fourth-harmonic laser output. In this paper, we investigate the variation in 456 nm and 228 nm laser output power under the cavity length of 63 mm. Ultimately, at a pump power of 41.75 W, the highest average power of 670 mW was achieved for a 456 nm blue laser output with a repetition rate of 12 kHz and a pulse width of 32 ns. Additionally, a maximum average power of 18 mW was obtained for a 228 nm deep ultraviolet laser output, featuring a repetition rate of 12 kHz and a pulse width of 33 ns.

2-W continuous-wave and passively Q-switched Tm,Ho:YLF channeled waveguide laser at 2.05 µm.

We report on the operation of an efficient Tm,Ho:YLF depressed cladding, channeled waveguide laser in both continuous-wave (CW) and passively Q-switched (PQS) regimes, producing laser emission at the wavelength of 2.05 µm. The 70-µm diameter depressed cladding waveguide, fabricated using femtosecond laser inscription, had a low propagation loss value of 0.14 dB/cm and a refractive index contrast of 8.3 × 10-4. In the CW regime, the waveguide laser was excited at 780 nm, and an output power of up to 2 W was generated at the incident pump power of 4.14 W with a power slope efficiency of 50.0%. PQS operation was further realized by utilizing a Cr:ZnSe saturable absorber (SA), whereby the waveguide laser generated as short as 19.6-ns pulses with a power slope efficiency of 18.9%.

Narrow-Pulse-Width, Straight-Type-Cavity, All-Solid-State Laser at 228.5 nm

Deep-ultraviolet (DUV) lasers operating at a wavelength of 228 nm offer distinct advantages in Raman spectroscopy and analysis, demonstrating significant potential in the field of surgical medicine. This paper details the development of a high-repetition-rate, narrow-pulse-width, short-cavity laser system functioning at 228.5 nm, which is based on Barium Borate (BBO) electro-optic Q-switching. The system utilizes a double-concave resonator structure and a pressure-applied electro-optic Q-switching technique, incorporating Lithium Borate (LBO) and BBO as frequency-doubling crystals. A low-concentration Nd:YVO4 crystal, measuring 4 mm × 4 mm × 5 mm, serves as the gain medium, with a high-reflectivity coating applied to its left end face to function as the total reflection mirror within the resonant cavity. Upon achieving a pump power of 37 W at a repetition rate of 12 kHz, the system produced a maximum average power of 32 mW, with a pulse width varying from 2.48 ns to 2.70 ns and a central wavelength of 228.5 nm, which is effectively applicable for deep-ultraviolet spectral detection.

Low-threshold absolute parametric decay instability of microwave beam in X2 ECRH experiments with monotonic density profile

It is shown that the absolute parametric decay instability of a microwave beam of a finite width, resulting in the excitation of two electron Bernstein waves, can occur at monotonic parameters of the background plasma in X2-mode ECRH experiments at a modest pump power. The excitation of daughter waves, whose power deposition localization differs from that of the pump wave, can potentially explain the broadening of the power deposition profile and lack of the pump power absorbed in the electron cyclotron resonance layer that has been found in X2-mode ECRH experiments.

Effect of pore plugging on transpiration cooling performance implemented with perforated flat plates

Transpiration cooling is expected to be one of the most effective cooling technologies for gas turbine blades. However, dust deposition can easily lead to pore plugging, which limits its practical application in engineering. The plugging of pores in conventional porous media models is difficult to predict, so it is essential to construct computational models with finely controllable porous structures. In this study, a transpiration cooling configuration with straight holes perforated with a diameter of 0.5 mm was adopted. The effects of plugging ratio and region on flow and heat transfer under different coolant injection ratios and pump power conditions were investigated by numerical simulation. The results showed that at constant mass flow rate, the overall cooling performance increased as the plugging ratio increased at low injection ratios. At high injection ratios, the opposite was true. With a certain pump power, as the plugging rate increased, the flow loss coefficient rose, leading to a decrease in cooling efficiency. Transpiration cooling efficiency was also highly sensitive to the distribution of plugged holes at the same plugging ratio. When the coolant flow was sufficient, the farther the plugged area was from the leading edge, the smaller the reduction in cooling efficiency.

Demonstration of UV-A stimulated emission from optical pumping with a nano-porous cladding layer

Abstract We report a room-temperature ultraviolet-A (UV-A) stimulated emission from a multiple-quantum-well laser diode featuring a nano-porous bottom cladding layer on the GaN substrate. For a 1500×15 μm ridge-type edge-emitting laser, we achieved a 372.8 nm emission under optical pumping, with a full-width-half-maximum (FWHM) of less than 2 nm and a threshold optical pumping power density of less than 1.2 MW cm−2. The integration of a nano-porous cladding layer effectively minimizes lattice mismatch, enhances confinement factor, and maintains electrical conductivity. This demonstration expands the potential for developing high-performance UV laser diodes on GaN substrates, overcoming limitations previously imposed by critical thickness contrasts.

1.45 ps All-solid-state Q-switched mode-locked laser based on new material Bi2Te3/Sb2Te3

In this work, the improvement of material properties and the optimization of mode-locked devices are discussed. The lateral heterojunction Bi2Te3/Sb2Te3 is prepared by a simple solvothermal method to overcome the limitation of traditional single material and improve the nonlinear optics properties. Based on a Bi2Te3/Sb2Te3 saturable absorber, the stable passive Q-switched mode-locked operation with wavelength of 1064 nm is achieved in Nd: YVO4 crystal. When the pump power reaches 5.5 W, a Q-switched mode-locked output with a maximum power of 910 mW is obtained, and the corresponding optical–optical conversion efficiency is 16.5 %. The repetition frequency of Q-switched pulse envelopes is 83.81 kHz, the pulse width is 1.8 μs, and the pulse energy is 10.8 μJ. The repetition frequency of the mode-locked pulse in the Q-switched envelope is 312.8 MHz and the pulse width is 1.45 ps. This flexible tunable laser provides high peak power, narrow pulse width, and highly stable laser output, broadening its application prospects in high-performance pulsed lasers.

Synergistic Nonreciprocity of Linear and Nonlinear Optical Diffraction.

Linear optical diffraction of light is a basic natural phenomenon subject to a long history study and it obeys the well-known reciprocity in transport. In this work we report observation of synergistic nonreciprocal linear and nonlinear diffraction of a Ti:sapphire femtosecond laser beam against a periodic poled lithium niobate (PPLN) thin plate nonlinear grating with a front surface corrugated with a shallow grating of a depth only 67nm and a smooth back surface. A high peak power pump laser beam shining upon the geometrically asymmetric nonlinear grating from either the front surface and back surface will both cause significant second-order nonlinear (2nd-NL) Raman-Nath diffraction and Cerenkov radiation, in addition to apparent linear optical diffraction and modest third-order nonlinear (3rd-NL) spectral broadening. These linear, 2nd-NL, and 3rd-NL optical processes all exhibit significant differences between the front-back forward and back-front backward transport processes, in that the linear and 2nd -NL nonlinear diffraction have distinctly different patterns, while the 3rd-NL spectral broadening extent is different. The apparent synergistic nonreciprocal linear and nonlinear diffraction can be ascribed to the different coupling strength between the linear, 2nd -NL, and 3rd-NL processes of pump laser within the PPLN nonlinear grating in the forward and backward pump. The observation of both strong nonreciprocal linear and nonlinear optical diffraction would enrich the concept and physics of fundamental optical reciprocity and nonreciprocity laws.

Research on flow structure and heat transfer mechanism of windward bend lattice frame

The lightweight lattice sandwich structure is considered a promising heat transfer technology with broad application prospects for improving the heat dissipation capacity of thermal management systems. The heat transfer performance needs to be further researched urgently. In this study, the flow resistance and heat transfer characteristics of windward bend lattice frames with heat transfer and mechanical load capacity were investigated by experimental and numerical methods. The flow mechanism and enhanced heat transfer mechanism of windward bend lattice frame was revealed from the point of view of unit structure. The results show that the bending shape alters the flow state of the fluid in the passage within the windward bend lattice frame truss to enhance the mixing effect of high-temperature and low-temperature fluids in the passage. Additionally, as the angle of inclination increases, there is a significant improvement in local flow resistance characteristics and enhanced heat transfer performance due to deflection in movement direction and rotation direction of inverse spiral vortex at rear truss rod. Furthermore, it is observed that at constant pumping power, the changes in Angle of inclination significantly affect heat transfer on different surfaces: lower surface (increasing by 101%), upper surface (increasing by 57%), followed by end wall (increasing by 16%). This work has valuable engineering applications for structures with similar bending characteristics.

Acousto-optic Q-switched broadband tunable single-longitudinal-mode 2 μm laser using a birefringent filter

Single-longitudinal-mode pulse lasers operating at a wavelength of 2 μm are extensively utilized as lidar light sources in gas detection applications. We demonstrated a tunable single-longitudinal-mode acousto-optic Q-switched Tm:YAP laser by a birefringent filter and etalon. With the absorbed pump power of 8.95 W, the laser achieved a pulse duration of 139 ns and a single pulse energy of 1.37 mJ at 1 kHz repetition rate, with an SLM ratio exceeding 99.5 %. The central wavelength was tunable over a wide range from 1887 nm to 2003 nm by adjusting the birefringent filter. Our results provide an effective approach for developing compact mid-infrared solid-state lasers with high power, wide tuning and excellent performance.

Covering a 1280–1495 nm (215 nm) wideband high-gain bismuth-doped fiber amplifier with only 1240 nm pumping

In this study, two bismuth-doped fibers were fabricated by atomic layer deposition (ALD) combined with modified chemical vapor deposition (MCVD) technology. For a dual-pump amplification configuration, 1240 and 1310 nm pumping the BDF simultaneously, when the 1240 nm pump power changes, it has little impact on the gain. The 1310 nm pump wavelength overlaps with the emission range of bismuth active centers associated with phosphorus (BACs-P), potentially suppressing its excitation. The experiment reveals that the emission range of BACs associated with silicon (BACs-Si) overlaps the absorption range of BACs-P, indicating that BACs likely exist for their reabsorption properties. Furthermore, enhancing the reabsorption properties can increase the luminescent intensity of BACs-Si in the 1420 nm region with only a 1240 nm pump. The gain of peaks at 1340 and 1420 nm exceeds 31.5 dB at a −23 dBm input signal. Notably, the gain within the 1280–1495 nm range exceeded 15 dB, achieving a bandwidth of 215 nm. This holds significant promise for applications in artificial intelligence, autonomous driving, and other fields with high-capacity communication demands.

Weak mode locking dynamics in a thulium-doped fiber laser

In this work, we study partial mode locking dynamics in a figure-eight thulium-doped fiber laser. With this particular laser design, which includes a long, highly power-imbalanced NOLM, two regimes are successively identified as pump power is raised, both characterized by a narrow-linewidth emission consisting of broad periodic pulses emerging from a dominant background radiation. In each case, peculiar dynamics are identified. In the first regime, the pulses undergo dynamical evolution at two different time scales: at the scale of hundreds of cycles, a slow quasi-periodic modulation affects both the pulse intensity and temporal position, whereas at the scale of the pulse duration, the inner details of its complex profile are found to drift under the pulse envelope. These phenomena are interpreted in terms of slow and fast gain dynamics, respectively. In the second regime, the waveform displays large Q-switched-like oscillations whose details reveal both the peak power clamping effect of the NOLM nonlinear transmission and competition between the pulse and the spurious background radiation. Finally, reducing pump power yields a quasi-continuous-wave regime in which the temporal waveform displays a self-imaging effect, as complex features in the temporal map repeat with a periodicity of 4.81 cavity cycles. Such behavior strongly contrasts with the stochasticity expected for this type of regime. These results illustrate the complex operation of long thulium-doped fiber lasers producing pulses in the 2-micron region, which are attractive for fundamental research, and also for applications such as surgery.