New designs and simulations of a 10-kW average-power longitudinally pumped dye laser amplifier

New designs of a 10-kW average-power longitudinally pumped dye laser amplifier pumped by a copper laser and its operating simulations are presented. The new designs, which use a center-hole mirror, make it possible to pump longitudinally without dichroic mirrors. The simulations take into consideration the time-dependent excited-state absorption of both the laser and the pump beam. Dye laser amplifiers, with an input dye laser average power of 10 kW, are simulated. The simulation results suggest that a better than 50% extraction efficiency can be obtained with two pump beams of more than 1 kW. The results also suggest that an amplified gain of 10 with an extraction efficiency of approximately 50% can be obtained with the double-pass amplifier.     

Dynamic model of multipass ultrashort-pulse laser amplifiers and its application

We developed a dynamic model for evaluating the gain and amplified spontaneous emission of multipass ultrashort-pulse laser amplifiers. This model takes into account the time dependence of the population inversion that is due to the time-varying pump power and the evolution of the amplified spontaneous emission. For gain media of a short upper-state lifetime, a time-dependent analysis is essential for the model to extend beyond order-of-magnitude estimation. We verified the model with a femtosecond dye laser amplifier. The calculated output energy is accurate to within +/-5% of the experimental data. We utilized this model to optimize the conversion efficiency of the dye laser amplifier under low-energy pumping. An efficiency of 2.3% is achieved with an optimal pump energy of only 4 muJ.     

Characteristics of a dye laser amplifier transversely pumped by copper vapor lasers with a two-dimensional calculation model

A two-dimensional rate equation model, taking into consideration the transverse absorption loss of pump laser power, is proposed to evaluate the characteristics of a dye laser amplifier with a large input laser beam diameter pumped by high average power copper vapor lasers. The calculations are in good agreement with the measurements taken with a Rhodamine 6G dye, and the model can be used for evaluation of the dye concentration at any wavelength.     

Extraction efficiency of saturated-gain high-power dye laser amplifiers: effect of nonlinear signal absorption

The effect of nonlinear signal absorption (NLSA) due to ground-state absorption and excited-state absorption in a transversely pumped high-power dye laser amplifier is theoretically examined with a one-dimensional steady-state model for a dye amplifier pumped by a copper vapor laser. A well-approximated analytical expression for the extraction efficiency is derived, from which the effect of NLSA in reducing the amplifier efficiency can be appreciated immediately and can also be interpreted in terms of certain characteristic lengths. The reduction in efficiency due to NLSA is found to be largely independent of the pump power, provided that the signal power is increased linearly with the pump power to continue to saturate the amplifier gain and suppress amplified spontaneous emission.     

A High Average Power Dye Laser Powered by a Vortex Stabilized Flashlamp

A flashlamp pumped organic dye laser has recently been operated at an average power output of 114 W. This is the highest average power ever reported for a dye laser. The laser was excited by a high power, vortex stabilized flashlamp. In this type of lamp a fast flow of argon gas is injected near the walls. The gas swirls inward and exits through holes in the electrodes. The fast gas flow provides cooling to allow the lamp to operate at high average power and it also stabilizes the position of the discharge. The lamp was used in an elliptical pumping cavity, with the lamp at one focus. The arc length in the lamp was 10 cm. The dye was circulated through a transverse flow channel at the other focus. The lamp was fired at repetition rates up to 357 Hz and with an energy per pulse of 211 J, i.e. an average power of 75 kW. The laser output pulses had a full width at half maximum of 1·8 μ sec. The average power output increased nearly linearly with repetition rate to a maximum of 114 W at 255 Hz. The achievement of even higher powers was limited by the replacement rate of dye in the channel and a drop in the flashlamp intensity at higher repetition rates. The dye used in these experiments was Rhodamine 6G in an ethanol solution.     

Generalized formula for continuous-wave end-pumped Yb-doped material amplifier gain and laser output power in various pumping configurations

We present a general formula fitted for computing the amplification and laser output power in a Yb-doped material under various quasi-end-pumping configurations. These configurations include single pass pumping, backreflection pumping in which the pump is reflected by a mirror set on the rear face of the amplifier medium, contrapropagation pumping where two pump beams are launched on both sides of the amplifier and, for every configuration, regenerative pumping in which the transmitted or reflected pump beam is recycled using the proper apparatus. We show that, with regenerative pumping, the efficiency is drastically improved and the optimum amplifier length leading to the maximum laser output power is shorter compared with the one obtained with conventional pumping. In this model, we do not take temperature effect into account.     

High-efficiency, argon-laser-pumped Nd:YLF laser system

An Ar-ion laser was used to pump a Nd:YLF laser, in both σ and π polarizations, in a longitudinal scheme. In spite of the small absorption coefficient at the pump (~0.25 cm (-1)), a careful laser design can circumvent this problem, and efficiencies as high as those attained with semiconductor pumping schemes are reported. The laser fundamental parameters were experimentally determined. A double-pass net gain as high as 10(3) was measured, and an output power of 1 W was obtained with a pumping power of 6 W.     

Oscillation characteristics analysis of transversely and coaxially pumped Ti-diffused Nd:MgO:LiNbO3 waveguide lasers

Abstract

A theoretical analysis of oscillation characteristics is developed for Ti-diffused Nd:MgO:LiNbO₃ waveguide lasers by using the formalism of mode overlap. Simple and explicit expressions in terms of mode sizes are derived for effective mode volume and coupling efficiency between pump mode and laser mode, which are directly proportional to the threshold pump power and slope efficiency, respectively, both for transverse and coaxial pumping considering the spatial distribution of the pump beam and the laser beam. A comparison for the two pumping configuration has shown that the transverse pumping requires much higher input pump power and has much lower slope efficiency than the coaxial pumping. The fundamental transverse mode (TM ₀) oscillation conditions relative to the cavity loss are also discussed for the two pumping configurations.

Indexing terms: Ti-diffused Nd:MgO:LiNbO ₃ waveguide laser, effective mode volume and coupling efficiency, threshold pump power and slope efficiency, transverse and coaxial pumping, single mode oscillation condition.     

Model of the nonlinear operation of a laser with a gaussian mirror

Abstract

In this paper a semi-classical model of the nonlinear operation of a laser is extended to describe a laser with a Gaussian mirror. Modified nonlinear self-consistent equations including transverse and longitudinal field dependence, gain saturation, spatial hole burning and nonlinear dispersion effects are derived. With the help of an energy theorem an approximate solution for steady-state single mode operation is presented, which relates the small signal gain to the output power and the laser system characteristic parameters. The laser output power characteristics are presented for various cavity configurations, especially, revealing an influence of the Gaussian mirror parameter on the power efficiency of the laser.     

Linewidth reduction by 6 orders of magnitude of a broad-area 729-nm diode laser

Diode lasers with a power output superior to 100 mW are in widespread use in medical as well as research applications. However, for such diodes lasing oscillation generally occurs simultaneously in several longitudinal and transverse modes that are unsuitable for high-resolution spectroscopy. We spectrally narrow a 100-mW broad-area diode laser by first using an extended cavity and then an electrical feedback produced by a Pound-Drever-Hall stabilization on a low-finesse reference cavity. Reduction of the linewidth by more than 6 orders of magnitude is achieved (the output linewidth is narrowed from 1 THz to less than 500 kHz), making possible its use for high-resolution spectroscopy. The power and the spectral qualities of this diode laser allow us to induce quantum jumps toward the D5/2 metastable level of single Ca+ ions.     

Spectroscopic properties and amplified spontaneous emission of fluorescein laser dye in ionic liquids as green media

The use of ionic liquids (ILs) as milieu materials for laser dyes is a promising field and quite competitive with volatile organic solvents and solid state-dye laser systems. This paper investigates some photo-physical parameters of fluorescein dye incorporated into ionic liquids; 1-Butyl-3-methylimidazolium chloride (BMIM Cl), 1-Butyl-3-methylimidazolium tetrachloroaluminate (BMIM AlCl₄) and 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIM BF₄) as promising host matrix in addition to ethanol as reference. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to the transition dipole moment, the attenuation length and oscillator strength were also investigated. Lasing characteristics such as amplified spontaneous emission (ASE), the gain, and the photostability of fluorescein laser dye dissolved in different host materials were assessed. The composition and properties of the matrix of ILs were found that it has great interest in optimizing the laser performance and photostability of the investigated laser dye. Under transverse pumping of fluorescein dye by blue laser diode (450 nm) of (400 mW), the initial ASE for dye dissolved in BMIM AlCl₄ and ethanol were decreased to 39% and 36% respectively as time progressed 132 min. Relatively high efficiency and high fluorescence quantum yield (11.8% and 0.82% respectively) were obtained with good photostability in case of fluorescein in BMIM BF₄ that was decreased to ∼56% of the initial ASE after continuously pumping with 400 mW for 132 min.     

Double-clad 10-W Yb3+-doped fiber master oscillator power fiber amplifier for He3+ optical pumping

We describe an all-fiber ytterbium-doped laser followed by a double-stage ytterbium-doped double-clad fiber amplifier of 10-W output power for helium pumping. Different cavity designs are investigated with the goal of achieving high-power multimode emission at 1083 nm, wavelength tunability over the helium absorption bands, and linewidth envelope control over the range 1-3 GHz. We point out the domains with unstable output power and discuss their origin.     

Theoretical modeling of a diode-pumped Nd:YAG laser with a solid nonfocusing pump light collector

We report theoretical modeling for a diode-side-pumped Nd:YAG laser in which the laser rod is fixed in a solid nonfocusing (prismatic) light collector. The geometry provides for pumping the rod from four sides, which gives a relatively uniform gain profile across the transverse section of the rod and enables a high tolerance of the laser output to resonator and pump diode misalignment. The numerical model is developed to illustrate how the pumping uniformity and the transfer efficiency are affected when changes in the collector and lasing materials are made. We use small-signal gain measurements to test the predictions of the model and to examine the extent to which surface scattering from the rough rod barrel further spatially averages the deposited pump energy. The effects of the different refractive indices of the rod, collector, and fixant and the absorption properties of the laser material on optical transfer efficiencies are discussed.     

High-power dye laser using steady-state amplification with chirped pulses

Steady-state chirped-pulse amplification was applied to a five-stage dye amplifier system to extract available energy over the full gain duration and at the same time suppress the amplified spontaneous emission (ASE). An output energy of 41 mJ was generated with 1.4-ns chirped pulses having an ASE of 3% and a pumping efficiency of 8.8% for the final amplifier. After five-stage amplification these pulses were compressed to 320 fs FWHM.     

Numerical analysis and experimental results of high-power Er/Pr:ZBLAN 2.7 microm fiber lasers with different pumping designs

Gain factor and output performance of erbium-praseodymium codoped ZBLAN double-clad fiber lasers at 2.7 microm with different pumping designs were calculated and analyzed. Single-end backward pumping with a highly reflective mirror butted against one fiber end and dual-end pumping with Fresnel reflections from both fiber ends were found to be the most efficient pumping designs. Ten-watt-level Er/Pr:ZBLAN fiber lasers proved to be achievable with recent diode laser and ZBLAN fiber technologies. Their corresponding optimum fiber lengths for different pumping configurations were determined. It was also found that fiber lasers with a flat evolution of gain factor can obtain the largest output power. Experimental results of 4 m and 12 m fiber lasers showed very good agreement with simulation results.     

Performance of diode-end-pumped Cr, Nd:YAG self-Q-switched and Nd:YAG/Cr:YAG diffusion bonded lasers

Self-passively Q-switching of a diode-pumped Cr,Nd:YAG, where the Cr⁴⁺ is used as a saturable absorber for the 1064 nm laser emission is reported. The maximum average output power was obtained using an output coupler of R=86%. The self-Q-switched diode pumped laser yielded 1.86-W average output power with low threshold pumping power (≈1.7-W), average slope efficiency of ≈34%, pulse duration of about 14–16 ns, and modulation frequency ranging from 2.4 to 73 kHz, depending on the input pumping power. These results are the highest reported for self-Q-switched lasers. Higher slope efficiency (42%) and shorter Q-switched pulses were obtained for a Q-switched Nd:YAG/Cr⁴⁺:YAG diffusion bonded laser. A comparison of the codoped Cr,Nd:YAG laser performance, with that of a diffusion bonded laser is reported and analyzed.     

One GeV acceleration with laser wakefield in the linear regime

We derive an expression for the maximum energy gain of an accelerated electron, in the limit that the plasma wave created by a laser wake is linear both along the longitudinal direction and in the transverse plane, and with a maximum laser power lower than the critical power for relativistic self-focusing. With an available power of 300 TW, the energy gain is of 1 GeV.     

One GeV acceleration with laser wakefield in the linear regime

We derive an expression for the maximum energy gain of an accelerated electron, in the limit that the plasma wave created by a laser wake is linear both along the longitudinal direction and in the transverse plane, and with a maximum laser power lower than the critical power for relativistic self-focusing. With an available power of 300 TW, the energy gain is of 1 GeV.     

A CuBr laser with high efficiency in the double-pumping-pulse mode

The results of examination of characteristics of a CuBr laser operated in the double-pumping-pulse mode with a lasing pulse repetition rate of 50 Hz are presented. The potential to enhance the laser efficiency by choosing the optimum voltages of dissociation and excitation pulses and time delay values is discussed. It is confirmed that a more than twofold increase in the laser efficiency may be achieved through optimization and matched injection of the excitation-pulse energy into the active medium plasma. A laser efficiency as high as 2.6% (with respect to an excitation pulse) with an average power of 16 mW, an energy of 0.32 mJ, a halfamplitude laser pulse duration of 40 ns, and a time delay of 150 μs is demonstrated. The maximum average radiation power is 37 mW with an energy of 0.7 mJ and a laser efficiency of 0.7% at an energy density of 24 (2.7) mJ/cm³ of a dissociation (excitation) pumping pulse.     

L波段掺铒光纤超荧光光源和放大器研究

通过优化铒光纤长度,获得了平坦谱宽达30nm(0.7dB)的L波段超荧光光源,该光源具有7.21dBm的输出功率。在此基础上,研究L波段放大器增益特性,通过对铒光纤长度的进一步优化,用1480nm激光器作前向泵浦源,实验上获得了波长从1565nm~1595nm范围平坦的增益带宽,小信号增益可达22dB。