Increase In Pump Energy Research Articles

Pure-quartic soliton self-frequency shift in a mode-locked fiber laser

The pure-quartic soliton (PQS) offers the advantage of a wide spectrum and approximately Gaussian temporal profile, which has the potential to obtain high-energy ultrafast laser pulses. Thus, exploring the role of stimulated Raman scattering in the formation and propagation of PQSs in fiber lasers is crucial, especially considering the greater propensity for highpower and short PQS pulses compared to traditional solitons. Here, we present the modeling of a self-frequency shift (SFS) fiber laser based on the PQS, emphasizing the impact of fourth-order dispersion and the Raman effect. The significant red-shift in wavelength is discovered as the pump energy increases, revealing that the emergence of SFS is a universal attractor in mode-locked PQS fiber laser systems. Our simulations demonstrate that such wavelength tunability is a direct byproduct of the gain bandwidth limit and the stimulated Raman scattering for PQSs inside the fiber cavity, while the evolution dynamics in the gain and passive fiber show obvious differences. However, we find that the effect of SFS in a PQS fiber laser is compromised by a trade-off with the degradation of pulse quality, such as reshaping the oscillating tail and destroying the symmetry of the emission pulse. This Raman-induced nonlinear process under high pump energy facilitates the discovery of the comprehensive complexity of science for PQSs suffering from higher-dimensional forms of nonlinear effects in fiber lasers.

Nd, Gd:SrF<sub>2</sub> crystal spectrum gain characteristic study on the broadband laser amplification

Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses. In this paper, the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF<sub>2</sub> crystal, i.e. the emission spectrum has a certain width at the higher stimulated emission cross section. Through the numerical simulation, the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail. Theoretical calculation shows that the spectral gain narrows obviously with the increase of gain values of the traditional Gaussian emission spectrum and increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing. Furthermore, the spectral gain narrowing characteristics of the Nd,Gd:SrF<sub>2</sub> crystal were studied experimentally. The Ф13mm×150mm Nd,Gd:SrF<sub>2</sub> crystal was used as the gain medium which was pumped by flash lamps in the experimental study. The experimental results show that the output spectra of Nd,Gd:SrF<sub>2</sub> crystals are not obviously narrowed when the input laser spectral width is 5nm (FWHM) and the gain is 140 times. The experimental results are consistent with the theoretical calculation and analysis. The crystal can work normally at the repetition rate of 0.2Hz and 1Hz in the experiment, but due to the influence of thermal effect, the gain will decrease to a certain extent with the increase of pump energy and repetition rate. The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.

Nd, Gd:SrF<sub>2</sub> crystal spectrum gain characteristic in broadband laser amplification

Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses. In this paper, the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF<sub>2</sub> crystal, i.e. the emission spectrum that has a certain width at the higher stimulated emission cross section. Through the numerical simulation, the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail. Theoretical calculation shows that the spectral gain is narrowed obviously with the increase of gain value of the traditional Gaussian emission spectrum, and that increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing. Furthermore, the spectral gain narrowing characteristics of the Nd,Gd:SrF<sub>2</sub> crystal are studied experimentally. The <i>Ф</i> 13 mm× 150 mm Nd,Gd:SrF<sub>2</sub> crystals are used as the gain medium which are pumped by flash lamps in the experimental study. The experimental results show that the output spectra of Nd,Gd:SrF<sub>2</sub> crystals are not obviously narrowed when the full width at half maximum (FWHM) of spectral width of the input laser is 5 nm and the gain is 140 times. The experimental results are consistent with the theoretical calculation and analysis. The crystal can work normally at a repetition rate of 0.2 Hz and 1.0 Hz in the experiment, but due to the influence of thermal effect, the gain will decrease to a certain extent with the increase of pump energy and repetition rate. The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.

Heat transfer and thermoregulation within single cells revealed by transient plasmonic imaging

Summary Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism, which is related not only to fundamental cellular functions but also massive applications. Unfortunately, thus far, we still know little about the heat transfer properties at the cellular or subcellular levels. Here, we demonstrated a transient microscopic method to measure the heat transfer in single cells. The thermal conductivity of different regions within a single cell shows a wide heterogeneity, and heat transfer in the region near the cell membrane is more active than the central region. However, the median values of thermal conductivity between different individual cells are quite close. A cellular-level heat regulation that responds to environmental temperature is observed in warm-blooded humans and chickens rather than in cold-blooded bullfrogs. According to the temperature-dependent cell metabolism, we proposed a hypothesis for cellular control of heat dissipation, which might be the cellular-level foundation of body thermoregulation.

Energy and Exergy Analysis of the Condensate Pump During Internal Leakage from the Marine Steam Propulsion System

An energy and exergy analysis of the condensate pump from the marine steam propulsion system during the condensate leakage between pump stages is presented in this paper. Measurements from the steam propulsion system during exploitation were necessary for collecting all the data for the condensate pump analysis. Due to condensate leakage inside the pump casing, the producer specified condensate pressures at the pump outlet could not be obtained during the exploitation. Low condensate pressure at the pump inlet and condensate temperature slightly above the atmospheric significantly influences the pump exergy analysis. Increase in pump load resulted in an increase of pump energy and exergy losses and efficiencies. In the observed load range during the leakage, pump energy losses are between 19.88 kW and 24.78 kW, while pump energy efficiencies are between 11.12 % and 41.54 %. Pump exergy losses are slightly higher, while exergy efficiencies are slightly lower when compared to energy losses and efficiencies. During normal operation, without leakage, the pump energy efficiencies are from 5 % to 20 % higher in comparison with pump operation when the leakage occurs.

Energy and Exergy Analysis of the Condensate Pump During Internal Leakage from the Marine Steam Propulsion System

An energy and exergy analysis of the condensate pump from the marine steam propulsion system during the condensate leakage between pump stages is presented in this paper. Measurements from the steam propulsion system during exploitation were necessary for collecting all the data for the condensate pump analysis. Due to condensate leakage inside the pump casing, the producer specified condensate pressures at the pump outlet could not be obtained during the exploitation. Low condensate pressure at the pump inlet and condensate temperature slightly above the atmospheric significantly influences the pump exergy analysis. Increase in pump load resulted in an increase of pump energy and exergy losses and efficiencies. In the observed load range during the leakage, pump energy losses are between 19.88 kW and 24.78 kW, while pump energy efficiencies are between 11.12 % and 41.54 %. Pump exergy losses are slightly higher, while exergy efficiencies are slightly lower when compared to energy losses and efficiencies. During normal operation, without leakage, the pump energy efficiencies are from 5 % to 20 % higher in comparison with pump operation when the leakage occurs.

4.24 μm mid-infrared laser based on a single Fe2+-doped ZnSe microcrystal.

In this Letter, we report for the first time, to the best of our knowledge, a micron-sized mid-infrared Fe2+:ZnSe laser based on a single microcrystal. Typical laser emissions centering at 4.24μm are observed from a selected Fe2+-doped ZnSe microcrystal under 2.94μm excitation of Er:YAG laser at room temperature. The laser linewidth is ∼10 nm, the pulse width is ∼50 ns, and the lasing threshold is ∼7.4 mJ/pulse. The lasing wavelength is stable as the pump energy increases and is consistent with the strong absorption position of carbon dioxide in the atmosphere.

Passive Q-switching of a Tm:YLF laser with a Co2+ doped silver halide saturable absorber

We report a successful passive Q-switching of a Tm:YLF laser operating at λ = 1.9 μm, using a Co2+:AgCl0.5Br0.5 saturable absorber. Approximately 200-ns long, 150 μJ pulses were obtained. Increase in pump energy resulted in repetitive pulsing, with a repetition rate approximately proportional to the pump pulse energy. Room-temperature optical transmission saturation curves measured in ∼1-mm thick Co2+:AgCl0.5Br0.5 plates yielded a ground state absorption cross section σgs=(7.8±0.5)×10−18cm2, and an excited state absorption cross section σes=(3.3±0.3)×10−18cm2, at λ = 1.9 μm. The lifetime of the A2(4F) second excited-state of the octahedral O symmetry was τ∗=(0.6±0.06)ns.

A high-order external distributed feedback polymer laser with low working threshold

In this paper, we report a high-order distributed feedback (DFB) polymer laser with low working threshold. Using the high-order grating increases the lithographic tolerances, providing coherent light sources that are more amenable to mass-manufacturing techniques, such as laser direct writing lithography and roll-to-roll processing. To enable high-order DFB lasing, an unconventional working configuration is designed in which the grating is situated on top of the uniform conjugated polymer film. In addition, a novel Forster energy transfer blend of two conjugated polymers is used as the gain medium. Upon pumping, the device emits lasing around 603.6 nm with a bandwidth of 0.5 nm. The threshold is around 20.5 μJ cm−2 (~2.56 kW cm−2), about to enter the regime of inexpensive LED pumping. A further increase in pump energy results in simultaneous oscillations at the 29th and 30th Bragg orders. Operating principles of the high-order DFB polymer laser, including spectral performance and threshold dependence on pump length, are investigated. This approach represents a step towards low-cost, even ‘disposable’ polymer lasers.

Random lasing in Cr:ZnS microstructure-textured grooves

We report a random lasing emission based on microstructure-textured grooves of Cr:ZnS crystal. The microstructures include horizontal ripples and a vertical periodic structure with dozens of micrometers of periods, which are induced by the Fresnel diffraction of femtosecond laser in the grooves and the interference of laser light through the micropores, respectively. The microstructures multiple-scatter the light, resulting in lasing emission with a center wavelength of 2250 nm and a relatively low lasing threshold of ~80 μJ/pulse. There is a dramatic shortening of the emission lifetime as the pump energy increases. The emission peaks are shifted by pumping at the microstructures with different vertical periods. It shows a structural stable property for potential random laser applications.

Ring-shaped backward stimulated Raman scattering driven by stimulated Brillouin scattering.

Backward stimulated Raman scattering is generated in water, pumped by pre-compressed pulses from a single-cell stimulated Brillouin scattering pulse compressor. The maximum energy efficiency of 9% is achieved by employing a circularly-polarized pump pulse at its energy of 50 mJ, around which point the backward stimulated Raman scattering also exhibits a ring-shaped profile. The correlations between spatial and temporal profiles as well as the intensities of the backward stimulated Raman and the stimulated Brillouin scattering generated from Raman cell indicate that the ring-shaped backward stimulated Raman is driven by intense stimulated Brillouin scattering. We demonstrate the latter process to be much more efficient for the backward Raman generation than the conventional process in which the laser itself pumps a backward stimulated Raman beam. It is shown that a further increase in pump energy leads to a drop in efficiency, combined with a break-up of the ring pattern of backward stimulated Raman. These effects are associated with filament generation above a certain threshold.

Luminescence properties and kinetic analysis of singlet oxygen from fullerene solutions

A systematic investigation on singlet oxygen (O2(a1Δ)) photoluminescence (PL) from fullerene (C60) solutions by using a pulsed Nd: YAG laser at 532nm was reported. The results show that the O2(a1Δ) PL intensity first increases linearly, then declines fast, and eventually tends to level off with the increase of pump energy, while decreases monotonically with increasing irradiation time. The latter can evidently be attributed to the formation of photoinduced O2(a1Δ) quenchers, which was directly confirmed by the remarkable decrease of O2(a1Δ) lifetime with increasing irradiation time. Also, we further demonstrated that the O2(a1Δ) quencher should be C60O via electrospray ionization-mass spectrometry (ESI-MS) and a kinetic analysis on the formation rate of the O2(a1Δ) quenchers in irradiated C60 solutions. On this basis, the above pump-energy dependence of O2(a1Δ) PL was also rationalized kinetically. With the increase of pump energy, the initial linear increase is exactly attributable to the linear increase of O2(a1Δ) concentration, while the following drop should result from the fast formation of photoinduced O2(a1Δ) quenchers and the eventual smooth variation is evidently related to the inverse saturated absorption effect of C60.

An unusual pulse compression of stimulated Brillouin scattering in water

Pulse compression is an important property of stimulated Brillouin scattering (SBS), and the SBS pulse duration becomes smaller with the increase of pump energy. An unusual pulse compression was investigated of the stimulated Brillouin scattering in water, it was found that the SBS pulse duration becomes larger as the pump energy increases. The pulse duration of SBS alters differently with the change of pump energy in strong focusing and weak focusing. Numerical simulation of pump light transmission in water cell has been made to explain the unusual pulse compression phenomena. Different real gain lengths in strong and weak focusing make different SBS pulse compression.

High-Power Terahertz Radiation Based on a Compact Eudipleural THz-Wave Parametric Oscillator

Tunable high-power THz-wave radiation is achieved via a compact eudipleural THz-wave parametric oscillator. The maximum THz-wave output is 1.164 V at 1.755 THz when the pump energy is 90mJ. In the experiments we find that the maximum output of THz-wave moves to the high frequency band as the pump energy increases and this phenomenon is reasonably explained. The polarization characteristics of the THz-wave are analyzed.

Tunable two-photon pumped lasing from alloyed semiconductor nanoribbons

Single-crystal ZnS1−xSexnanoribbons with various compositions were synthesized through an Au-catalyzed vapor transport method. Under two-photon pumping with an 800 nm femtosecond pulsed laser, the spontaneous emission peak of the ternary nanoribbons undergoes a gradual red-shift from 422 to 464 nm with the increase of Se content. When the pump energy densities are increased above the thresholds, the nanoribbons exhibit a tunable upconverted laser emission accompanied by a dramatic decrease in spectral linewidth as a set of sharp peaks on the corresponding wavelengths of each sample, featuring the occurrence of stimulated emission. Two components appear in the fluorescence lifetimes, which indicate that the ZnS1−xSexnanoribbons have two different recombination centers. Both lifetime components decrease with the increase of pump energy, further confirming the occurrence of stimulated emission. The two-photon pumped lasing behavior was also observed from single nanoribbons, in which the photoluminescence (PL) spectra are composed of multimode of lasing. The distinct modes show gain competition and pronounced shifts as a function of excitation density.

Improved output energy characteristic of optical limiting based on double stimulated Brillouin scattering

In order to improve the optical limiting performance based on stimulated Brillouin scattering (SBS), a method based on double SBS is proposed in this paper. The dependence of the output energy of optical limiting based on double SBS on the pump energy is numerically simulated, and experimentally validated with an Nd:YAG seed-injected laser. The results indicate that only the first SBS optical limiting works in the case of low pump energy. However, as the pump energy increases, the second SBS process can be activated if the transmitted power of the first SBS is still above the SBS threshold. Therefore, the output energy characteristic of optical limiting based on double SBS is much better than that based on single SBS. Owing to the sub-nanosecond response time and a high power threshold, the SBS optical limiting can provide protection in high power laser systems.

Principle of the Phase Controlling of the SBS Wave and its Application to the Beam Combination Laser for the Laser Fusion Driver

The phase control of the stimulate Brillouin scattering (SBS) wave by a standing wave is the most important technique for the realization of the beam combination laser system. In this work, a theoretical model has been developed for explaining the principle of the phase controlling. The phase fluctuation of the SBS wave has been numerically calculated using this theoretical model. Consequently, it predicts the phase of the SBS wave will be stabilized as the fluctuation of the pump energy decreases and the pump energy increases. Furthermore, the change of the relative phase difference between the SBS waves can be easily calculated by this model in the beam combination laser system.

Ultrashort pulse generation in cw solid-state lasers with semiconductor saturable absorber in the presence of the absorption linewidth enhancement

A theory for ultrashort pulse generation in cw solid-state lasers with a `slow' semiconductor saturable absorber in the presence of self-phase modulation in the active medium and absorption linewidth enhancement in the semiconductor has been developed. It was shown that with increase of pump energy the laser switches from stable ultrashort pulse generation to bistable operation regime. The parameters for stable ultrashort pulse generation were found.

Nonlinear dispersion effects in a broadband Raman amplifier

We report the dependence of Raman gain on the correlation between the pump and the Stokes waves in a broadband Raman amplifier. Experimentally, the Raman correlation function is obtained by measurement of the Stokes output energy as a function of pump delay. When the Stokes wave precedes the pump, the Stokes output is larger than in the opposite case. The correlation function becomes more asymmetric as the pump energy increases. We propose that this asymmetry is caused by the nonlinear Raman dispersion. Using a multimode model, we perform numerical simulations to confirm this idea. The results of the simulations agree well with the experimental data.