Pump Power Research Articles

Excess Intensity Noise in a Nonlinear Amplifying Loop-Mirror-Based Mode-Locked Laser from a Non-Reciprocal Phase Bias

We demonstrate a low-intensity-noise, nonlinear amplifying loop-mirror-based mode-locked fiber laser by optimizing the polarization of the non-reciprocal phase bias and the pump current. If the angle of the waveplate in the non-reciprocal phase bias to the polarization axis of a polarization-maintaining fiber is not carefully aligned, parasitic polarization is induced. The parasitic polarization affects the minimum pump power and dynamic range of pump power for mode-locking, the intensity noise, and the comb power. To reduce intensity noise, the angle of the waveplate for the non-reciprocal phase bias is adjusted, and then the pump power is adjusted. The waveplate angle minimizing the intensity noise maximizes the dynamic range of the pump power for mode-locking and output power. As a result, the relative intensity noise has been suppressed by more than 32 dB at 15 kHz Fourier frequency. The polarization extinction ratio at the non-reciprocal phase bias is critical since it can determine a cavity loss and quality factor of a laser oscillator. Therefore, the additional polarizers cannot improve the intensity noise once the angle is mismatched and the polarization extinction ratio is degraded.

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.

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.

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.

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.

Two types of stimulated emission in HPHT diamond with a high concentration of NV centers

The paper presents the results of experimental observation of two types of stimulated emission (SE) under pulsed laser pumping at 532 nm in diamond with NV centers. A comprehensive spectroscopic characterization of multisectorial HPHT diamond plate was performed. At low pumping power, the stimulated emission from NV¯ centers was recorded as a broad (≥80 nm wide) band with a maximum at 706 nm in the {111} and {311} sectors of the diamond plate. As the pump power increased in the {111} sector, narrow-band stimulated emission (<10 nm wide) was detected, with a maximum at 716 nm and a luminescence impulse duration of 1.5–3 ns. As the pump density increased, a fine structure in the spectrum of narrow-band stimulated emission was revealed for the first time. The concentration of NV¯ centers in the {111} and {311} growth sectors was ≈10 ppm. However, there were considerable differences in the concentrations of C (35 and 3.5 ppm) and C+ centers (6.1 and 3.2 ppm, respectively). It was demonstrated that the presence of a high concentration of NV¯ centers is not the only necessary condition for the initiation of narrow-band SE in the 710–720 nm range. In the {311} sector, lighting at 360, 405, and 488 nm reduced the concentration of NV¯ centers by 15 % while increasing the concentration of C+ centers in the {311} sector. This effect is weak in the {111} sector. The authors suggested a model for narrow-band SE at the transition Valence Band → C+ with charge-state conversion of C↔C+ and NV0↔NV¯ centers. Further research on the dynamic processes is required in order to a detailed understanding of the operation of NV centers in diamond during SE generation.

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.

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.

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.

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.

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

Abstract We report 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 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 less than 1.2 MW/cm2. 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.

High capacity performance signature of micro optical mechanical system switches based fiber Bragg grating scheme implementation in optical WDM data routed center networks

Abstract This paper demonstrated the high capacity performance signature of micro optical mechanical system switches based fiber Bragg grating scheme in optical wavelength division multiplexing data routed center networks. The FBG reflectivity is simulated versus near infrared operating wavelength region with relative refractive index difference of Δn = 0.1 %. Required optical pump power, temperature increment and FBG power dissipation or consumption are demonstrated versus FBG wavelength spacing at pumping wavelength of 1,480 nm for doped/undoped fiber. Required FBG mechanical switching voltage, and required FBG mechanical/thermal switching time are clarified at pumping wavelength of 1,480 nm for doped/undoped fiber. Grating period and Bragg wavelength is studied against effective refractive silica/polymer FBG index.

Influence of pump spectrum on stimulated Brillouin scattering part 1: analysing SBS threshold

An expression for the threshold power of stimulated Brillouin scattering (SBS) in optical fibres is derived for pumps with arbitrary power spectra. It is compared to spectrally independent approximations for the SBS threshold and is found to be in close agreement when the assumptions used for the approximations are applied. This expression is then used to examine the variation of the SBS threshold with pump power spectrum. The analysis of the results shows a significantly lower SBS threshold than that predicted by the more commonly used expressions. Additionally, a connection is made between decreasing the pump power spectral density, which is dependent on spectral shape of the pump, and increasing the SBS threshold power.

A comparative study of pump-probe photothermal spectroscopy using mach-zehnder interferometer and in-fiber mode interferometer

We report a comparative study of mid-infrared photothermal spectroscopy using a Mach-Zehnder interferometer and an in-fiber mode interferometer using a tellurite hollow-core antiresonant fiber (HC-ARF). A quantum cascade laser (QCL) at 5.26 µm serves as the pump laser and is coupled into the HC-ARF to detect nitric oxide (NO). In both interferometric setups, a 1.55 µm probe laser is used to measure the phase variation induced by absorption. The Mach-Zehnder interferometer uses a servo-loop feedback control to achieve quadrature point operation, while the mode interferometer uses passive stabilization based on common mode rejection. With a fiber length of 35 cm, we achieve a noise equivalent concentration of 60 ppb with the Mach-Zehnder interferometer and 0.8 ppb with the mode interferometer. In addition, the response of the sensor to modulation parameters, gas concentration, pump power and long-term stability is also discussed in this study.

NbSe2/PtTe2 heterostructures as saturable absorbers for mid-infrared pulsed solid-state lasers.

We have realized for the first time, to the best of our knowledge, a 2µm nanosecond solid-state passive Q-switched Tm:YAP laser based on a N b S e 2/P t T e 2 heterojunction saturable absorber. At an incident pump power of 12.69W, the Tm:YAP laser produces stable laser pulses with a minimum pulse width of 818ns, a maximum single-pulse energy of 15.48µJ, and a peak power of 18.93W at a repetition rate of 79.44kHz. The comparison results show enhanced saturable absorption performance compared to single N b S e 2 (1µs, 70.32kHz) and single P t T e 2 (1.31µs, 71.97kHz). The experimental results confirm that the N b S e 2/P t T e 2 heterojunction is a promising saturable absorption material that can be used to realize high-performance mid-infrared pulsed lasers. The resulting nanosecond 2µm Q-switched pulsed laser will play an important role in atmospheric monitoring, lidar, and other fields, and can provide a strong driving force.

Mo0.5W0.5S2 as saturable absorber for passively mode-locked Tm:YAP laser

In recent years, 2 μm pulsed lasers have received extensive attention from researchers due to their wide applications in materials processing and medical fields. In this work, we reported preparing Mo0.5W0.5S2 saturable absorber (SA) via liquid phase exfoliation and successfully using this SA in Tm:YAP lasers to generate passively mode-locked (PML) pulses. An average output power of 0.87 W was achieved with the injected pump power of 20.38 W in the PML Tm:YAP laser, corresponding to a slope efficiency of 4.8%. Moreover, a pulse width of 686.4 ps at 85.9 MHz was acquired with a central output wavelength of 1935 nm from the laser, and the beam quality of M2 was measured to be 1.10 and 1.12 in the X and Y directions. The potential of Mo0.5W0.5S2 material in the transition metal dichalcogenides family for saturable absorption property in the 2 μm region was demonstrated by this work.

Modeling of Graded-Index Raman Fiber Amplifiers with Pump Depletion

Graded-index (GRIN) fibers are often used for making high-power Raman amplifiers. We employ numerical and semi-analytical techniques to model such amplifiers and include not only the signal’s amplification and pump’s depletion but also various nonlinear interactions between the signal and pump beams and the self-imaging effects within the GRIN fiber. We solve the coupled nonlinear equations of the pump and signal beams numerically. We also employ the variational technique to obtain simpler equations that can be solved much faster than the full model and still agree with it in most cases of practical interest. We discuss the evolution dynamics of the pump and signal beams, along with a novel process of energy exchange between the two beams because of self-imaging inside the GRIN fiber. The dependence of the signal’s amplification on various input parameters is analyzed in detail to optimize the device’s design and enhance the signal’s amplification for a given pump power and fiber length. Based on our analysis, we establish a resonant condition for the maximum energy transfer from the pump to the signal being amplified. We further show that the periodic self-imaging of the pump and signal beams inside a GRIN fiber leads to higher output powers compared to step-index fibers.