High-power Diode-pumped Lasers Research Articles

Strengthening of very large crystalline and polycrystalline Nd:YAG rods for high-power laser applications

A multistep thermochemical etching procedure was applied to very large Nd3+:YAG rods to increase their fracture strength. The strengthening procedure combined selection of high-quality material, fine centerless grinding, thermochemical etching, and (after completion of the lapping, polishing and AR coating) an additional hot thermochemical etching, with rod ends protected with poly-tetra-fluoro-ethylene (Teflon) caps. The final cleaning step, not previously reported, is essential in removing fracture causing contaminations on the rod surface. A unique thermal load-to-fracture technique was applied on test rods to measure their fracture strength. The rods were thermally loaded up to fracture by means of optical pumping in a specially designed laser pump chamber. The results thus obtained were analyzed by Weibull distribution statistics appropriate to these tests. The strengthened laser rods of this study sustained a maximum pump power density of $$ I_{{\ell_{\hbox{max} } }} $$ = 500 W cm−1. This value is higher by a factor of four over untreated rods and also higher than any previously published data for such large rods. High-power diode-pumped laser heads were operated with the strengthened crystalline and polycrystalline Nd:YAG rods, yielded output power of ~ 3 kW, when pumped with 7 kW. Such performance was routinely achieved without any instance of rod fracture. Reliability of the strengthening procedure was further demonstrated by the failure-free operation of an azimuthally polarized high-power master-oscillator power-amplifier system (composed of oscillator, preamplifier, and six power amplifiers), emitting an output power in excess of 10 kW.

Laser performance of diode-pumped Yb:CaF_2 optical ceramics synthesized using an energy-efficient process

Due to their natural toughness, and also their flexible and cheap production process, laser ceramics could provide an interesting alternative to single crystals for meeting the challenges posed by the demanding domain of ultrafast and high-power laser operations. We investigated the laser performance of a Yb:CaF2 ceramic developed with a simple and green synthesis process. A 4 at. %-doped ceramic sample was diode-pumped to deliver output power of 1.6 W with optical-to-optical efficiency reaching 25%, a slope efficiency of 43%, a gain of 1.4, and wavelength tunability from 1015 to 1060 nm. Results are comparable to the typical single Yb:CaF2 crystal performance, thereby enabling the applications of these greener and low-cost Yb:CaF2 ceramics in high-power diode-pumped lasers.

Challenges of high power diode-pumped lasers for fusion energy

Abstract This paper reviews the different challenges that are encountered in the delivery of high power lasers as drivers for fusion energy. We will focus on diode-pumped solid-state lasers and we will highlight some of the main recent achievements when using ytterbium, cryogenic cooling and ceramic gain media. Apart from some existing fusion facilities and some military applications of diode-pumped solid-state lasers, we will show that diode-pumped solid-state lasers are scalable to inertial fusion energy (IFE)’s facility level and that the all-fiber laser scheme is very promising.

High-power diode-pumped cryogenically cooled Yb:CaF_2 laser with extremely low quantum defect

High-power diode-pumped laser operation at 992-993 nm under a pumping wavelength of 981 of 986 nm is demonstrated with Yb:CaF₂ operating at cryogenic temperature (77 K), leading to extremely low quantum defects of 1.2% and 0.7%, respectively. An average output power of 33 W has been produced with an optical efficiency of 35%. This represents, to the best of our knowledge, the best laser performance ever obtained at such low quantum defects on intense laser lines.

High power cw and mode-locked oscillators based on Yb:KYW multi-crystal resonators

We report on a high power diode-pumped laser using multiple bulk Yb:KY(WO(4))(2) (KYW) crystals in a resonator optimised for this operation. From a dual-crystal resonator we obtain more than 24 W of cw-power in a TEM(00) mode limited by the available pump power. We also present results for semiconductor saturable absorber mirror (SESAM) mode-locking in the soliton as well as positive dispersion regime with average output powers of 14.6 W and 17 W respectively.

Growth and characterization of Nd:Y_xGd_1−xVO_4 series laser crystals

A series of Nd:YxGd1−xVO4 (x=0.17, 0.37, 0.53, 0.63, 0.70, 0.81) mixed laser crystals with doping concentration of 0.5 at.% Nd were successfully grown by the Czochralski method. Thermal properties including the specific heat, thermal diffusion coefficient, and the thermal conductivity were systematically studied. The material constants Ms were calculated and show that the thermal fracture limit of the mixed crystals should be comparable with that of Nd:YVO4. Diode-pumped continuous-wave (CW) laser performance at 1.34 μm and 1.06 μm with a- and c-cut crystals was demonstrated. The influence of different x values on laser performance and emission cross sections was also discussed. All the results show that Nd:YxGd1−xVO4 represents a new series of crystals suitable for application as high-power diode-pumped lasers.

Laser performance and thermal lensing in high-power diode-pumped Yb:KGW with athermal orientation

A comparative, experimental study of the high-power diode-pumped laser performance and thermal lensing properties between standard b-cut Yb:KGW and Yb:KGW cut along an athermal direction is presented. The results show that thermal lens properties in both the b-cut and the athermal direction-cut crystals are determined by anisotropic thermal expansion in Yb:KGW. Thermal gradients due to the pump beam cause thermal lensing even in the athermal direction-cut geometry. The thermal lens is much weaker and less astigmatic in the athermal direction-cut crystal, for the same absorbed power. These properties allow generation of better-quality laser beams with the athermal direction-cut crystal as compared to the b-cut crystal.

An Experimental Comparison of Linear and Parabolic Tapered Waveguide Lasers and a Demonstration of Broad-Stripe Diode Pumping

This paper compares the laser performance of linear and parabolic tapered waveguides in ion-exchanged Nd:Glass, finding significant advantage for the linear guides, with demonstrated adiabatic expansion to widths of 250 /spl mu/m. The characterization of these waveguide lasers by Ti:sapphire pumping is followed by a demonstration of high-power diode-pumped laser operation and a discussion of the optimization of such a scheme for producing high-power integrated-optics laser sources.

Laser operation of a low loss (0.1 dB/cm) Nd:Gd 3Ga 5O 12 thick (40 μm) planar waveguide grown by pulsed laser deposition

Waveguiding films of Nd:Gd 3Ga 5O 12 with a thickness up to 40 m have been fabricated by pulsed-laser deposition on Y 3Al 5O 12 (1 0 0) substrates. A laser threshold of 18 mW of absorbed pump power has been obtained and lasing action has been observed at 1060.6 nm for pump powers close to the lasing threshold, and at both 1059.0 and 1060.6 nm at pump power levels of approximately 1.5 times above threshold. Waveguide propagation losses of 0.1 dB/cm have been obtained by measuring the absorbed pump power threshold for laser operation at 1060.6 nm for a range of output couplers with various reflectivities. Slope efficiencies of 12.3% and 17.5% were derived using output couplers with a transmission of 2.2% and 4.5%, respectively. The combination of low propagation losses and high numerical aperture for the waveguides indicates the potential of the fabrication technique to produce high quality thick multi-layer waveguides. Such designs are suitable for the development of high-power diode-pumped laser sources of near-diffraction-limited beam quality.

High-power planar dielectric waveguide lasers

The advantages and potential hazards of using a planar waveguideas the host in a high-power diode-pumped laser system are described. Thetechniques discussed include the use of proximity-coupled diodes,double-clad waveguides, unstable resonators, tapers, and integrated passiveQ switches. Laser devices are described based on Yb3+-, Nd3+-, andTm3+-doped YAG, and monolithic and highly compact waveguide laserswith outputs greater than 10 W are demonstrated. The prospects for scalingto the 100 W level and for further integration of devices for addedfunctionality in a monolithic laser system are discussed.

Multiwatt, tunable, diode-pumped CW Yb:GdCOB laser

We demonstrate that Yb-doped Ca4GdO(BO3)3 (GdCOB) crystals are suitable for the development of high-power diode-pumped lasers emitting at around 1.04 μm. A 15%-doped Yb:GdCOB crystal was longitudinally pumped with a cw fiber-coupled diode emitting 10 W at 976 nm. While 5.2 W of diode power was absorbed, we obtained 3.2 W of 1043-μm laser light, with a beam quality factor M2 equal to 3, and 2.5 W in a diffraction-limited beam. Furthermore, the laser is continuously tunable between 1018 and 1086 nm. Thermal effects have been investigated with a Shack–Hartmann wavefront analyser: although thermal lensing is not negligible, it does not affect the performance of the laser with the resonator design we used.