High-power Laser Generation Research Articles

Generation of high power laser at 1314 nm from a diode-side-pumped Nd:YLF module

We demonstrate a high power continuous-wave (CW) and acoustic-optically (AO) Q-switched 1314-nm laser with a diode-side-pumped Nd:YLF module. A maximum CW output power of 21.6 W is obtained with a diode pump power of 180 W, corresponding to an optical-to-optical conversion efficiency of 12.0% and a slope efficiency of 16.1%. In the Q-switching operation, a highest pulse energy of 3.8 mJ is obtained at a pulse repetition rate of 1 kHz. The shortest pulse width and maximum single peak power are 101.9 ns and 37.3 kW, respectively.

High-power Yb-doped continuous-wave and pulsed fibre lasers

High-power laser generation using Yb-doped double-clad fibres with conversion efficiencies in excess of 80% have attracted much attention during the last decade due to their inherent advantages in terms of very high efficiency, no misalignment due to in-built intracore fibre Bragg gratings, low thermal problems due to large surface to volume ratio, diffraction-limited beam quality, compactness, reliability and fibre-optic beam delivery. Yb-doped fibres can also provide a wide emission band from ∼1010 nm to ∼1170 nm, which makes it a versatile laser medium to realize continuous-wave (CW), Q-switched short pulse, and mode-locked ultrashort pulse generation for various applications. In this article, a review of Yb-doped CW and pulsed fibre lasers along with our study on self-pulsing dynamics in CW fibre lasers to find its role in high-power fibre laser development and the physical mechanisms involved in its generation has been described. A study on the generation of high-power CW fibre laser of 165 W output power and generation of high peak power nanosecond pulses from acousto-optic Q-switched fibre laser has also been presented.

Yb3+ doped fluorophosphate laser glasses with high gain coefficient and improved laser property

Yb3+ doped fluorophosphate glasses with high stimulated emission cross-section, large gain coefficient and low hydroxyl absorption coefficient were prepared by high temperature melting for fiber laser applications, and their spectral, general laser parameters were investigated accordingly by means of fluorescence emission spectrum, decay cure and infrared absorption spectra. Compared with previously reported fluorophosphate glasses, the investigated fluorophosphate glasses have highest grain coefficient and maintain a maximum laser systematical factor over other various types of laser glasses. The introduction of fluorides to fluorophosphate glasses results in the low level of hydroxyl absorption coefficient and concentration. All these advantages might mean that Yb3+ doped fluorophosphate glasses are a good candidate as an active laser media for short pulse, high power laser generation used for next generation nuclear fusion.

Laser welding and weld hardness analysis of thick section S355 structural steel

Laser welding is becoming increasingly common and has been found to be of particular interest in the welding of various steel structures. A new generation of high power lasers has entered the market during recent years. These lasers have thus far mostly been used for welding of thin sheet. However, with the availability of higher power, such lasers have possible application to thick section welding. This study investigates the performance and potential of deep penetration laser welding of S355 EN 10025 structural steel of 20 and 25 mm thickness with a high power fiber laser at power levels of 12–30 kW. Visual examinations of the macrographs and hardness tests of all welded specimens were made. Quality windows were drawn based on the results of the experiments. Preferable welding parameters are formed based on the experimental study. The results of the hardness test show that surface hardness level of the weld is up to 2.5 times higher than the surface hardness of the base material.

Fabrication and characterization of a water-free mid-infrared fluorotellurite glass

Using a physical and chemical dehydration technique and a high-pressure, ultradry O2 atmosphere in a semiclosed steel-chamber furnace, we fabricated a group of fluorotellurite glasses with a composition of (90-x)TeO2-xZnF2-10Na2O (mol.%, x=0-30). For x=30, no OH absorption was observed in the range of 0.38-6.1 μm. This is the first report of a water-free mid-IR fluorotellurite glass, to our knowledge, offering the common advantages of a robust oxide glass and an IR-transparent fluoride one. Besides optimized linear transmittance and absorption, the nonlinear refractive indices and Raman gain coefficients are reduced. These results are discussed in the context of mid-IR high-power laser generation and transmission.

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.

A numerical analysis of high power laser propagation in magnetized plasmas

A computer code has been described which predicts the interaction of a laser beam with a cylindrical plasma with an imbedded magnetic field. The code has been used to study the bleaching wave behavior, and the results have been compared with experiment for a particular case. The agreement with experiment is generally found to be good. The results should be considered as preliminary and the work is continuing on improving the sophistication of the code.

High-power laser propagation: Thermal blooming

This paper presents a tutorial review of the self-induced thermal distortion of laser radiation propagating in absorbing media. The distortion of the laser beam is the result of heating of the path by absorption of a small fraction of the laser beam power by the medium which changes the index of refraction and therefore distorts the beam. Thermal-blooming effects can limit the laser powers which can be effectively propagated through the atmosphere, or in media which absorb laser power such as industrial or laboratory environments, liquid or gas cells, or even laser active media themselves. In this paper, we review the steady-state thermal blooming of CW beams including laboratory-simulation experiments and computer-code results. The thermal distortion of pulsed-laser radiation is also covered including single-pulse thermal distortion and the distortion of a train of laser pulses. In these discussions, we derive and identify the scaling laws and determine the important nondimensional parameters so that the results can be interpreted and applied to other propagation conditions. The thermal-blooming problem can be complicated by a number of circumstances, such as the geometry of the propagation path, and these special cases are also reviewed. Among those covered are: the influence of stagnation zones, transonic flow, the kinetic cooling effect, molecular and aerosol absorption and relaxation, laser-beam jitter, and atmospheric turbulence. In addition, the techniques utilized to minimize blooming, such as laser-beam shaping, and adaptive-optics phase correction, are also discussed.

High power laser propagation

High power laser beams propagating in the atmosphere are subjected to a variety of effects, the most important of which are absorption, scattering, turbulence induced beam spreading and wander, thermal blooming, and gas breakdown. In this paper simplified models are used to show how the various atmospheric effects interrelate and impact on the best laser choice for high power applications through their dependence on the laser wavelength and temporal mode (e.g., cw or pulsed) of operation. Results for sea level propagation at seven common laser wavelengths varying from 0.34 microm to 10.6 microm. are presented that show the mid-ir wavelengths to be favored for typical turbulence and aerosol scattering conditions. At the longer 10.6-microm CO(2) laser wavelength thermal blooming is dominant due to stronger molecular absorption, while at the shorter wavelengths turbulence induced beam spreading and aerosol absorption and scattering effects become important and tend to limit the increase in irradiance expected on the basis of diffraction effects alone.

Review of high power laser propagation

Review of high power laser propagation