Multicore fiber lasers have larger mode areas, resulting in higher power thresholds for nonlinear processes such as
stimulated Raman scattering and stimulated Brillouin scattering. Because of longer distributed distance of the cores,
thermal mechanical effects are decreased compared with those of single-core lasers. Therefore, multicore fiber lasers are
proposed as a candidate for the power scaling. The progress of multicore fiber lasers is simply introduced. Optical fields
propagating in multicore fibers are coupled evanescently, resulting in what are called supermodes. In this article, the
coupled-mode theory for analyzing supermode of fiber transmission is introduced. By mean of the theory, assuming
under weak-coupling conditions, the supermodes are approximated as linear superposition of modes of individual cores
with appropriate coefficients. The near-field mode distributions of some supermodes are numerically calculated, and the
corresponding mode distribution patterns are drawn. For making the multicore fiber laser preferentially operate in a
particular supermode so that improving beam quality, an in-phase locking method based on self-imaging Talbot external
cavity is introduced.
In this paper, we report on the near-field distribution of multi-core photonic crystal fiber lasers. The supermodes of
photonic crystal fibers with foursquarely and circularly distributed multi-cores are observed. The supermode properties
are investigated by using full-vector finite-element method (FEM). The mode operations of our 16-core foursquare-array
and 18-core circular-array photonic crystal fiber lasers are simulated by the COMSOL Multiphysics software. The
near-field distribution patterns of in-phase supermode are presented.
We report a pulsed, widely tunable Ti:sapphire laser pumped by an all-solid-state Q-switched intra-cavity
frequency-doubled Nd:YAG laser with repetition rate of 7 KHz. Using two dense flint glass prisms as dispersion
elements, the output wavelength could be continuously tuned over 675-970 nm, with spectral line-width of 2 nm.
Gain-switching characteristics of Ti: sapphire laser shortened the pulse width to 17.6 ns. Well mode matching between
pump and laser beam in the sapphire crystal and thermal design of the cavity ensured stable, efficient laser operation.
The maximum output power was 6.2 W at 780 nm when the 532 nm pump power was 22 W; corresponding conversion
efficiency was 28.2%.
Three Nd:GdVO4 crystals with Nd3+doped concentrations of 0.1, 0.2 and 0.3 at% were involved in the experiment. Their laser characteristics at 1.34 μm were experimentally tested with a diode-end-pumped
configuration and a simple plane-parallel cavity. Maximum output powers of 7.3 W, 8.35 and 9.47 W were
achieved, respectively. The thermal stress resistances of these crystals were calculated according to the
experimental data.
This letter reports the CW red laser radiation at 659.5 nm by intracavity frequency doubling a side pumped Nd:YAG laser with a KTP crystal (type II phase match, Θ=59.8°, Φ=0°). The thermal lens effect related to the laser crystal is analyzed and parameters of the three-mirror folded cavity are calculated. To enhancing the high gain at 1319 nm of the operating wave of Nd:YAG, the reflectivity of the mirrors is designed, and the red laser radiation at 659.5 nm is achieved by intracavity frequency-doubling. The generation of 1.2 W of the CW red laser beam is obtained with 260 W pumped power.
We reported phase mismatch compensation of second harmonic generation with controlling boundary temperature of type-II KTP crystal in high power intracavity frequency-doubled Nd:AG laser. Thermal induced phase mismatching of the KTP crystal was analyzed theoretically by numerical computations of temperature derivative of refractive indices. The temperature gradient of the KTP crystal, phase matching angles change with difference boundary temperature of the KTP crystal, and tolerance temperature was analyzed. In the experiment, when two KTP crystals of difference type II phase matching condition (Φ=23.6°, Θ=90° at 27°C temperature, Φ=24.7°, Θ=90° at 80°C temperature) were applied to compensate the phase mismatching of the type-II KTP crystals. The maximum average 532nm output power of 85 W and 110W were generated when the boundary temperature of KTP were kept in 4°C and 48.8°C respectively. The corresponding conversion efficiency is 9.03% and 11%.
The stabilization and modes of a high-power intracavity frequency-doubled Nd:YAG laser are numerically analyzed, the great influence of frequency-doubler’s thermal lensing on the stabilization and modes of this laser is demonstrated, and a compensating method is developed. A high-power QCW 532 nm green laser has been fabricated in the experiment, with a KTP crystal (θ=90°, φ=24.7°, 6×6×9.2mm, cut for high-temperature (80°C) application) as frequency-doubler. With the KTP crystal warmed up to 48.8°C and resonator parameters adjusted optimum according to the calculated thermal focal length of KTP crystal, a maximum 110W green laser is generated at 10.6kHz repetition rate, and its pulse width is 142ns, instability 2%, and optical-to-optical efficiency 11%.
Disk fiber laser is a novel fiber laser. The pumping scheme of such type of fiber laser is side pumping by LD arrays and the pumping scale is large in comparison with the core pumping manner in a typical clad pumping scheme. More pumping power could be coupled into the disk and higher output power could be achieved. To optimize the system of disk fiber laser, it is necessary to analyze the parameter of each part of it. In this paper, the configuration factors that influence the pumping efficiency of disk fiber laser were analyzed and propagation of the rays in disk fiber laser was simulated using the method of BPM. In the process of simulation, the fiber was treated as cylindrical lens. The optimal position of pump resource is obtained with a fixed size of the fiber cross section.
High power laser-diode-pumped 532nm laser sources (including continuous wave and high repetition rate operation) are directly used for precise processing of metals and plastics. Furthermore, high power green laser will be used in some fields such as ocean exploration, laser probe and underwater communication. Recently, we reported a 110W diode-side-pumped Nd:YAG intracavity frequency doubled high stability 532nm laser. In the experiment, we found that the average output power of second harmonic fluctuated acutely with the variety of pumping current. Moreover, the length of arms between the mirrors were very sensitive to this cavity. We consider that one of the reason is the focus length of thermal lens of Nd:YAG rod alter with the variational pumping current, which makes the cavity be unstable. We consider the KTP crystal as a thin lens for its short length. As thermal lensing effect of the Nd:YAG rod is quite severe, so we consider it as thermal lensing medium. By ray matrix methods, we have obtained the stable regions and beam waist radii distribution in the flat-concave cavity. In our experiment, we used a pump head consisting of 80 diode bars with pentagon pump model and employed flat-concave cavity structure in order to achieve high stability output and increase output power. The total cavity length is 505mm. By using an acousto-optic Q-switching with high diffraction loss and the KTP crystal which is type II phase matching, 110 W high stability 532nm laser is achieved. The experimental result is in good agreement with the calculation.
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