High Average Power Solid State Research Articles

Robust method for long-term energy and pointing stabilization of high energy, high average power solid state lasers.

A robust and simple method is presented for ensuring constant energy and pointing of a high average power solid state laser on a target. In addition to providing long-term stability, this scheme also eliminates any drifts in energy or pointing resulting from the initial warm-up after a cold start. This is achieved using two separate feedback loops: one loop stabilizes the pointing of the beam external to the amplifier cavity and the other locks the cavity mode to have optimum overlap with the pump spot on the active medium. The key idea of the cavity mode stabilization is to monitor the overlap of the cavity mode and the gain medium with a camera and control it with an actively controlled, intra-cavity mirror. While this method is demonstrated on a thin-disk regenerative amplifier, it can also be applied to a wide variety of solid state laser amplifiers.

高平均功率固体激光器研究进展

高平均功率固体激光器研究进展

Thermally induced birefringence in Nd glass heat capacity disk laser

The temporal behavior of depolarization losses during the pumping and cooling phases in a flash lamp pumped Nd glass heat capacity disk laser is reported. We also investigated the influence of thermally induced birefringence on the laser performance by measuring the output energy and the deformation it produced in the probe beam. The complete two-dimensional thermal profile of the laser disk surface was measured for the determination of the thermal uniformity across the disk surface. A new concept for pumping the laser disk is proposed that can lead to a considerable reduction in the depolarization loss in the Brewster angle configuration and hence provide a high average power solid state laser with good beam quality.

Influence of addition of B2O3 on properties of Yb3+-doped phosphate laser glass

The three host glasses doped with Yb3+ were prepared by means of conventional melt quenching technology, and the influence on physical and spectral properties of phosphate glass due to addition of B2O3 was investigated and compared with silicate glass. The results show that due to the existence of OH− impurities which induce the non-radiative route, the fluorescence lifetime of phosphate glass is shorter, so silicate glass has better spectral properties than phosphate glass. Silicate glass has more excellent thermal-mechanical properties than phosphate glass, but with the addition of B2O3, thermal-mechanical properties of phosphate glass are improved greatly without fluorescence quenching effect, and this kind of borophosphate glass will be the candidate to be used in high average power solid state laser.

Investigation on Structures and Properties of Yb 3+-Doped Laser Glasses

The Yb 3+-doped silicate, phosphate and borophosphate laser glasses were prepared by means of conventional melt quenching technology. The physical and spectral properties of the glasses were investigated. The results show that, due to the existence of OH −, the fluorescence lifetime of phosphate glass is shorter than that of silicate glass, so silicate glass has better spectral properties than phosphate glass. Silicate glass has better mechanical and thermal properties than phosphate glass, but with the addition of B 2O 3, mechanical and thermal properties of phosphate glass are improved greatly without fluorescence quenching effect. This kind of borophosphate glass can be used in high average power solid state lasers.

Optimization of spectroscopic properties of ytterbium-doped laser glasses

Four laser glasses with high emission cross sections are experimentally obtained. The laser performance parameters are determined from the spectroscopic parameters of these glasses and compared with those of developing laser glasses abroad. It is shown that Yb3+-doped telluorogermanate, Yb3+-doped niobosilicate glasses have the highest emission cross section and gain coefficient, the smallest minimum pumping intensity and saturation pumping intensity, and the lowest minimum fraction of excited ions. Yb3+-doped borate glass follows just behind them. These glasses have some spectroscopic advantages over laser glasses developed recently elsewhere. Yb3+-doped phosphate glass is comparable to phosphate laser glass which had high emission cross section and was developed recently by HOYA Corporation in Japan. The domestic glasses with optimum spectroscopic properties may be promising candidates for applications in high-average power and high-peak power solid state lasers, especially laser for the next generation laser nuclear fusion facility.

Toughening and crack tip shielding in brittle materials by residually stressed thin films

The apparent fracture toughness of brittle components can be greatly enhanced via surface-deposited thin films which are under residual, possibly nonuniform compression since the residual compression counteracts the effect of the applied loads at the tip of a surface crack. Examples are epitaxial thin films on crystalline components, thin films in a state of compression due to the film deposition process, or thin films of ion-exchange in glass. We review the micromechanics of the strengthening process by considering a surface microcrack under the combined action of the residual stress in the film (which shields the crack tip and may cause partial crack closure) and of the externally applied loads (thermal or mechanical). We examine crack tip shielding as the interaction of microscopic dilatant spots with the crack tip. This model predicts rising crack growth resistance curves for limited amounts of crack growth. We review and analyze experimental results on ion exchange in thin films of glass in small-, medium-, and large-size glass components for high average power solid state lasers. These measurements show that the apparent fracture strength increases by as much as five to six times.