Specific Pump Power Research Articles

Time Jitter and Intensity Noise of an All-Fiber High-Power Harmonic Mamyshev Oscillator

The phase noise and relative intensity noise (RIN) of an all-fiber high-power harmonic mode-locked Mamyshev oscillator (MO) are experimentally investigated. Through characterize in detail the integrated time jitter (TJ) and RIN under different output power of each order of harmonic mode-locking, it is found that the integrated TJ/RIN gradually degraded with increasing the output power. In the meantime, the noise performance can be improved with increasing the repetition rate at a specific pump power. In addition, it is also found in the experiment that the stimulated Raman scattering (SRS) effect deteriorates the phase noise and RIN of the laser output considerably. At the highest output power of 3.62 W, the integrated TJ/RIN reduces from 2.88 ps/0.36% to 2.39 ps/0.24% after spectrally filtering out the SRS components. However, the autocorrelation trace of the compressed pulse shows no obvious change with and without the SRS components.

Yttrium Oxide (Y2O3) as a Pulse Initiator in a Mode-Locking Erbium-Doped Fiber Laser

Mode-locking is an ultra-short pulse laser generation technique. The range of pulse duration may vary from picoseconds to femtoseconds. Yttrium Oxide (Y2O3) based saturable absorber (SA) was appropriately revealed in the mode-locked method within the 1.55-micron regime. Y2O3 is perfect for strength, melting point, and chemical stability and can be used as a laminated insulator due to its properties. Moreover, Y2O3 also owns broadband service, switching speed, and engineering features. The Y2O3-PVA film was produced by combining the 50 mg Y2O3 powder into a 50 mL polyvinyl alcohol (PVA) solution and stirring it at room temperature for about 24 h. A mode-locked pulse was recorded with the integrated Y2O3-PVA SA in the erbium-doped fiber laser (EDFL) cavity, and the output spectrum optical spectrum analyzer displayed was around 1560.66 nm. In addition to the sustained mode-locked pulse, a nearly constant repetition rate of 1.01 MHz at a specific pump power begins from 175.87 mW to 228.04 mW while the pulse duration is 4.15 ps. Lastly, the mode-locked pulse had been evaluated, which showed the peak power started from 4.94 kW to 6.07 kW.

Spatiotemporal self-mode-locked operation in a compact partial multimode Er-doped fiber laser.

We report spatiotemporal self-mode-locked operation at 1.55 µm with a low pump threshold of 32 mW in a compact partial multimode fiber laser system. Spatial filtering and the saturable absorber, both of which originate from the multimode interference (linear or nonlinear) of the single mode-multimode structure in this hybrid configuration, are well suited to the spatiotemporal self-mode-locked operation. Not only stable multimode conventional solitons with different spectral bandwidths but also a multimode soliton molecule complex with different structural bound-state patterns are obtained. It is found that the spatiotemporal evolution of the multimode solitons is dependent on many factors, such as the operating state, the involved frequency component, and the interaction between solitons. Furthermore, an unstable spatiotemporal mode-locked (STML) state where the beam profiles of the solitons change spontaneously is also observed for a specific multimode fiber state and pump power.

Электроразрядный KrF-лазер с высокой удельной энергией излучения

Results of experimental and numerical studies of an electric-discharge KrF laser with a specific pump power of 3.5 and 7 MW/cm3 are presented; in this case, lasing was obtained with a specific radiation pulse energy of ~ 6 and 9.5 J/l, with an internal energy efficiency of ~ 4%. Time dependences of the formation of charged and excited particles in a dense excimer plasma with an electron concentration of ne ~ 1016 cm-3 are shown. Conditions for the effective operation of the laser are proposed, which will make it possible to ensure a further increase in the specific radiation energy by more than two times while maintaining the high internal efficiency of the laser relative to the energy deposited into the discharge.

An experimental heat transfer investigation of using spacer in direct contact membrane distillation

Membrane distillation (MD) is a thermally-driven separation technology that can produce highly pure water. Direct contact membrane distillation (DCMD), where both hot and cold solution is directly in contact with the hydrophobic membrane is the most studied system due to its condensation method without an external condenser as well as its overall structural simplicity. In this paper, heat transfer analysis was carried out in DCMD experimentally to investigate how the presence of a spacer can effect on heat transfer coefficient. Results revealed that the heat transfer coefficient for spacer-filled channels (plastic and metallic material) is approximately from 3 to 3.5 times higher than that for empty channels. Additionally, from specific pumping power (SPP) for 1 cubic meter of freshwater production, it is predicted that DCMD with spacer-filled channels can consume far less electrical or mechanical energy than that with empty channels.

Performance evaluation of oscillating flow regenerators filled with particles, wire screens and high porosity open-cell foams

The porous matrix filled in oscillating flow regenerators has a significant influence on the performance of the regenerators. In this study, we firstly simulated the heat exchange process of the oscillating flow regenerators with particles, wire screens and high porosity open-cell foams with water as the working fluid using a generalized one-dimensional two-phase thermal-hydraulic model. Then, a detailed evaluation on the performance of these three types of regenerators was carried out regarding unit volume weight, regenerator effectiveness, specific pumping power and the proposed comprehensive performance factor by us as evaluation criteria. The comprehensive performance factor proposed by us is suitable for the performance evaluation and optimizing design of the oscillating flow regenerators because it not only considers the heat exchange ability of the thermal energy by introducing the entransy, but also solves the mismatching between the thermal energy and the pumping power in quality by division operation instead of weighted average algorithm. The evaluating results indicate that high porosity open-cell foams are the optimal choice for the porous matrix used to oscillating flow regenerators from multiple perspectives. The greatest advantage of foams is their high porosity and low pressure drop compared to the other porous structures. This study could also provide a guideline for the other fields involving the porous matrix.

Efficient telecom to visible wavelength conversion in doubly resonant gallium phosphide microdisks

Resonant second harmonic generation between 1550 nm and 775 nm with normalized outside efficiency >3.8×10−4 mW−1 is demonstrated in a gallium phosphide microdisk supporting high-Q modes at visible (Q∼104) and infrared (Q∼105) wavelengths. The double resonance condition is satisfied for a specific pump power through intracavity photothermal temperature tuning using ∼360 μW of 1550 nm light input to a fiber taper and coupled to a microdisk resonance. Power dependent efficiency consistent with a simple model for thermal tuning of the double resonance condition is observed.

Discharge formation in a XеCl laser pumped by high specific power

Stable glow of the discharge of various types in the gas mixture of a XeCl laser is investigated for specific pumping power in the range 1.2–4.6 MW/cm3 and pulse duration of 40 ns. It is demonstrated that formation of partially homogeneous plasma with many intensive cathode spots on the electrode allows the maximum energy and duration of the lasing pulse to be obtained with laser efficiency of 2.4%. It is revealed that for the specific pumping powers up to 1.5 MW/cm3, a very homogeneous volume discharge with a small number of lowintensive cathode spots is formed in the discharge gap. With further increase in the specific pumping power exceeding 4.5 MW/cm3, current microinhomogeneities are formed in the volume discharge of this type leading to lasing breakdown.

Highly efficient pulse-periodic XeCl lasers

The parameters of electric-discharge pulse-periodic XeCl lasers with a pulse duration of 25 - 40 ns, an energy of 0.2 - 0.7 J, and a pulse repetition rate up to 100 Hz have been investigated. It is shown that the total laser efficiency of 2.6 % and the maximum efficiency with respect to the stored energy of 3.8 % are obtained at a specific pump power of 2.8 - 3.3 MW cm-3 and a discharge circuit inductance of 3.5 - 4 nH.

Amplification and generation of radiation at the 42Γ → 1,22Γ transition of the Kr2F molecule in an electron-beam-pumped wide-aperture laser

The radiation amplification and oscillation are obtained in an electron-beam-pumped Berdysh laser with an active volume of 10 L in the visible range from 430 to 470 nm at the broadband 42Γ → 1,22Γ transition in the triatomic Kr2F molecule of interest for amplification of ultrashort laser pulses. It is shown that, along with absorption of laser radiation in the active medium, the amplification dynamics is considerably determined by short-lived absorption induced in the amplifier windows by bremsstrahlung X-rays. For the specific pump power 0.6 — 0.7 MW cm-3, the gain, corrected for nonstationary absorption, was ∼10-3 cm-1. A scheme of a Kr2F amplifier is proposed for amplification of ultrashort pulses up to multiterawatt peak powers in the active volume ∼10 L.

Influence of the specific pump power on the output energy and efficiency of a 223-nm gas-discharge-pumped excimer KrCl laser

The influence of the specific pump power on the output energy and efficiency of a 223-nm gas-discharge-pumped KrCl excimer laser operating on the Ne—Kr—HCl and He—Kr—HCl mixtures is studied. The optimal specific pump powers are found at which the maximum values of the total efficiency and output energy of the KrCl laser are achieved. The optimal specific pump power for the Ne—Kr—HCl and He—Kr—HCl mixtures lies in the ranges from 5.0 to 5.5 MW cm-3 and from 5.8 to 6.5 MW cm-3, respectively. The output energy of 700 mJ at the efficiency 1.0% for the KrCl laser on the Ne—Kr—HCl mixture is obtained for the first time.

Nuclear-pumped laser operating in the master oscillator—amplifier regime

The efficiency of a master oscillator—amplifier scheme and the possibility of its using in multichannel nuclear-pumped laser systems are studied. The small-signal gain and saturation parameter are measured for the He:Ar:Xe = 380:380:1 mixture at a pressure of 1 atm at a wavelength of 2.03 μm. It is shown that the small-signal gain increases linearly with the specific pump power density and achieves 1.1—1.2 m-1 at a pump density of 40 W cm-3. The saturation parameter is almost independent of the pump power and is equal to 70—90 W cm-2. It is found that at the pump-pulse maximum (40 W cm-3) the laser radiation power increases after amplification by 100%.

Extractable energy from ytterbium-doped high-energy pulsed fiber amplifiers and lasers

An analytic model is developed to evaluate the extractable energy from high-energy pulsed ytterbium-doped fiber amplifiers and lasers. The energy extraction capabilities under the limitation of spurious lasing, due to amplified spontaneous emission, are mapped for various numerical apertures, single- and multitransverse-mode evolution, and operating wavelengths. The calculation results of the analytic model show a good match with experimental results carried out for various double-clad fiber amplifiers. The model provides an accurate assessment for the maximum pulse energy that can be extracted from a given ytterbium-doped fiber. In addition, for a specific pump power, the model can be used to determine the minimum repetition rate and optimal length, under which the laser source can be operated before spurious lasing occurs.

Influence of excitation parameters and active medium on the efficiency of an electric-discharge excimer ArF laser

The kinetic model of processes occurring in the plasma of an electric-discharge 193-nm excimer ArF laser operating on mixtures of He and Ne buffer gases is developed. The influence of excitation and active medium parameters on the lasing energy and total efficiency of the electric-discharge excimer ArF laser is studied theoretically and experimentally. It is shown that a specific pump power of ∼4.5–5.0 MW cm-3 is required for attaining the maximum lasing energy for the highest efficiency of an ArF laser operating on a He—Ar—F2 mixture. For the first time, the pulse energy of 1.3 J at an efficiency of 2.0% is attained for an ArF laser with a specific pump power of 5.0 MW cm-3 using mixtures with helium as a buffer gas.

Formation of a volume discharge in air at atmospheric pressure upon application of nanosecond high-voltage pulses

Volume self-sustained discharges in gases at high pressure are formed with the use of pre-ionization sources and are widely used for pulsed laser pumping [1, 2]. In a pulsed nanosecond discharge [3, 4], the conditions can be realized in which the time of discharge channel formation is less than the voltage pulse duration. Then the volume discharge is formed under conditions of multielectron initiation when the initial voltage exceeds the static breakdown voltage. In [5–9], the volume pulsed discharge was initiated in air and other gases at atmospheric pressure without preionization source. To this end, nanosecond high-voltage pulses (~100 kV and more) with a leading pulse edge duration of ~1 ns and less were applied to the gap in [5–9]. The anode was flat, and the cathode had a small radius of curvature. With increase in the interelectrode gap, a pulse corona discharge was observed under these conditions. The main difference between volume and corona pulsed discharges is that in the corona discharge, the gas is ionized only in a part of the gap with the highest electric field strength. In the volume discharge, the gas is ionized in the entire gap, which allows high current densities on the anode (~3 kA/cm), high specific deposited power (~1 J/cm), and high specific pump power density (~400 MW/cm) to be obtained [6–9]. The diffusion discharge with a brighter central channel was realized in [10] when the voltage pulse duration increased up to 170 ns and the leading edge pulse duration increased up to 10 ns. This means that the discharge constriction is observed with increasing pulse duration. However, in [5–10] much attention was given to the study of the discharge initiated in gaps with the potential cathode having a small radius of curvature, and the influence of voltage pulse polarity and a decrease in the strength of electric field applied to the gap on the formation of the volume discharge was not investigated. Only in [9] the volume discharge was realized in air at atmospheric pressure and near the tip anode (the electrode of a shear discharger). The volume discharges initiated in comparatively short interelectrode gaps or with preionization sources were investigated in [1–4]. The present study investigates the influence of polarity and radius of curvature of the electrodes on the formation of the volume pulsed discharge without pre-ionization source under application of nanosecond voltage pulses of comparatively high amplitude (~100 kV). In our experiments we used the pulse generator of the ARINA x-ray apparatus [4]. The open-circuit gap voltage was about 150 kV and the leading pulse edge duration was less than 1 ns. The voltage pulse polarity could be both positive and negative. The pulse duration at half-maximum was ~2 ns for the volume discharge. Three types of the potential metal electrodes were used, including a sphere 40 mm in diameter (electrode No. 1), a tube 6 mm in diameter fabricated from a foil 50 μm thick (electrode No. 2), and a tip (electrode No. 3). The electrode was connected through a metal rod to a peaking spark-gap of the ARINA apparatus and was placed into a chamber with an inner diameter of 160 mm fabricated from a copper foil. This chamber had a flat bottom used as the second electrode. The interelectrode gap could be increased from 20 to 70 mm. All investigations of the discharge formation were conducted in air at a pressure of 1 atm. During our experiments, the total discharge glow (Fig. 1) was registered together with current and voltage waveforms. As in [5–9], the volume discharge (Fig. 1a) was stably recorded when the voltage pulse of negative polarity was applied to the electrodes with a small radius of curvature (Nos. 2 and 3). Bright spots are seen only on the cathode; volume plasma jets started from these spots. In [6] the discharge of this type was called VADIEB (volume avalanche discharge

Repetitively pulsed operating regime of a high-pressure atomic xenon transition laser

The repetitively pulsed regime of an atomic xenon transition laser pumped by an electron beam with various pulse durations and an electron-beam-initiated discharge is studied experimentally. An average radiation power of 2.5 W has been achieved in a quasi-stationary regime for a pulse repetition rate of 5 Hz in a laser pumped by a radially convergent electron beam of duration 100 μs without circulation of the Ar — Xe working mixture. The average output power for a laser pumped by a planar electron beam in quasi-stationary regime is 2 W. It is shown that for a specific energy contribution not exceeding 50 J L-1 and laser excitation by a train of electron-beam pulses at a repetition rate of 50 Hz, the amplitude and duration of the second lasing pulse virtually coincide with those of the first. For a laser pumped by a discharge initiated by a nanosecond electron beam, an average lasing power of 380 mW is achieved under steady-state conditions upon transverse circulation of the working mixture and a pump pulse repetition rate of 25 Hz. Pumping by an electron beam from two accelerators with a pulse duration of a few tens of microseconds under an Ar — Xe mixture pressure of about 1 atm and a specific pump power of 1 — 3 kW cm-3 per pulse is proposed for the development of 1.73-μm repetitively pulsed Xe lasers with a high average output power.

Effect of molecular additions on the radiation parameters of a laser on Xe atomic transitions

An electron-beam-pumped laser on Xe atomic transitions is experimentally investigated at various pump durations and powers within wide ranges of pressures and working mixtures including additions of molecular gases. It is shown that the maximum specific lasing powers are achieved at high specific pump powers (above 200 kW cm-3 atm-1) and durations of the beam current pulse of tens of nanoseconds in high-pressure Ar — Xe mixtures with molecular gas additions (N2 and CO2). A specific output radiation power of ~ 4 kW cm-3 is obtained. For a pump pulse durations from hundreds of nanoseconds to 1 μs, the highest lasing energies are reached without molecular additions at a comparatively low beam-current density (the specific pump power is ~ 10 kW cm-3 atm-1). However, in setups with specific pump powers above 40 kW cm-3 atm-1 and a working-mixture pressure limited by the strength of the laser chamber, molecular additions result in an increase in the radiation energy and efficiency. In wide-aperture facilities with high pump powers, molecular additions improve the distribution of the radiation power density over the laser-beam cross section.

Analysis of the possibility of lasing on the third continuum in argon

The possibility of lasing on the third continuum in argon was studied theoretically. This possibility is considered from the point of view of two hypotheses on the nature of the third continua, which have survived through the mid-1990s. The gain was calculated under conditions when the oscillation is most probable, namely, in the pressure range between 1 and 30 bar for specific pump power in the range 10-3—10 MW cm-3 bar-1. The gain is shown to be negative under the above conditions and, hence, lasing cannot be achieved.

Dissociation of carbon dioxide in sealed-off CO2 waveguide lasers with radio-frequency excitation

A mathematical model describing the dissociation of carbon dioxide in sealed-off CO2 waveguide and slit lasers with radio-frequency excitation is presented. The theoretically calculated degrees of dissociation of CO2 were tested experimentally. It was demonstrated theoretically and experimentally that the degree of dissociation increases by 5% — 10% with increase in the specific pump power. It was established that the degree of dissociation of carbon dioxide in lasers with the slit design of the discharge channel was approximately 1.5 times higher than in the usual waveguide lasers.

Technical note: Optimizing the thermohydraulic performance of flat-plate solar air heaters operating with fixed⧸variable pumping power

The validity of the analytical criterion derived for predicting optimum channel depth of conventional Solar Air Heaters (SAHs) has been explored for other flat-plate models of practical importance. Compared to the conventional design with air-channel under the absorber, the considered two models have airflow over the absorber and on both sides of it, respectively. Particularly examined is the effect of channel depth-to-length ratio ( D⧸ L) on the performance characteristics of these single-pass SAHs. Performance simulation results confirm the applicability of the criterion for these models over a wide range of influencing parameters including specific pumping power (P), emissivity of channel surfaces and wind heat transfer coefficient. It is found that the criterion successfully estimates the channel depth parameter ( δ p) that optimizes the performance for fixed or variable pumping-power operation. For the latter mode of operation, however, the ratio D⧸ L = 3 ∗ 10 −3 is recommended. Also, the performance diagram of a particular model design can easily be generalized if it is rated in terms of the analytical parameters δ p and P⧸ L which tightens up the intimate dependence of heater performance on both channel dimensions and flow pumping power.