Gregory J. Quarles

Co-casting and optical characteristics of transparent segmented composite Er:YAG laser ceramics

A novel colloidal co-casting process was developed to fabricate laser quality, multisegment composite ceramic laser gain materials. The approach was demonstrated for a three segment transparent composite rod 62 mm long by 3 mm diameter consisting of undoped yttrium aluminus garnet (YAG), 0.25% Er:YAG, and 0.5% Er:YAG. The Er concentration profile in the composite has steep, controllable gradients at the segment interfaces, while maintaining constant dopant concentrations within each segment. The composite rod has 84% transmittance at 1645 nm (the lasing wavelength) with a scatter loss of 0.4% cm −1 . Laser operation of such a composite Er:YAG ceramic rod was demonstrated for the first time, with nearly equivalent lasing behavior to an Er:YAG single crystal rod.

Processing technology, laser, optical and thermal properties of ceramic laser gain materials

Recently there has been increasing interest in high quality ceramic laser gain materials, particularly for high-energy lasers, due to the successful application of high-volume advanced ceramics consolidation techniques to transparent oxide gain materials. In this paper, a brief comparison of manufacturing techniques is presented, including an overview of the co-precipitation process and the solid-state reaction process. Merits and risks of each will be presented from a processing viewpoint. Ceramic Nd:YAG in particular shows promise for high power laser design. The program reported here is also compiling a definitive database to compare ceramic and single crystal Nd:YAG materials. Uniform doping levels of up to 9 at% Nd3+ have been reported by Konoshima Chemical Co. in ceramic Nd:YAG, and studied by the US Army Research Laboratory and the US Air Force Research Laboratory. All ceramic Nd:YAG materials studied to date have exhibited similar, if not identical, spectroscopic parameters to those measured for single crystal samples. Thermal properties, laser damage thresholds and refractive indices for a range of temperatures and wavelengths are reported. Diode-pumped free running laser experiment results with highly concentrated (up to 8 at% Nd3+) ceramics and their comparison with our modeling results are presented. High pulse repetition frequency actively (AO) Q-switched laser experiments are in progress. While there are still challenges in the manufacturing of ceramic laser gain materials, and the benefits of the application of ceramic technology to laser material are yet to be fully realized, ceramic Nd:YAG shows promise and could provide new options to the laser design engineer.

Nd:LuLF operating on the 4 F 3/2 → 4 I 11/2 and 4 F 3/2 → 4 I 13/2 transitions

Nd:LuLF, that is, Nd:LuLiF4, was grown with a Czochralski technique and characterized spectroscopically to include absorption and emission data and lifetime. Evaluation of this laser material for operation on the 4F3/2→4I11/2 and the 4F3/2→4I13/2 transitions was performed. Normal-mode laser performance was achieved on both the π and the σ polarizations for both transitions by use of a simple polarization-selective resonator. Both normal-mode and Q-switched performance was characterized on the 4F3/2→4I11/2 transition.

Progress in the crystal growth of Ce : colquiriites

Abstract The search for an efficient solid-state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium-doped colquiriite crystals, such as LiCaAlF 6 (LiCAF) and LiSrAlF 6 (LiSAF). Unfortunately, the doping of LiSAF and LiCAF with Ce 3+ introduces different variables into the growth of high optical quality crystals, due to the charge imbalance induced when this trivalent ion substitutes for the divalent site. Charge compensation with Na + tends to produce a more uniformly doped crystal with improved laser properties. Although preliminary research indicated that Ce : LiSAF may be the preferred material of the colquiriite hosts, Ce : LiCAF has also proved to be quite promising.

Highly efficient diode-pumped Yb 3+ :Y 2 O 3 ceramic laser

The Q-CW output power in excess of 30 W and slope efficiency of 47.3% were obtained and are, to the best of our knowledge, the highest reported so far for diode-pumped Yb³⁺-doped Y₂O₃ laser.

High-power diode-pumped laser based on Yb3+:Y2O3 ceramic

We have performed a laser evaluation of the Yb3+-doped Y2O3 ceramic laser material. The Q-CW output power in excess of 30 W was obtained with the slope efficiency of 47.3%. This output power is, to the best of our knowledge, the highest reported so far for diode-pumped Yb3+-doped Y2O3 laser.

Material and laser characterizations of intermediate compositions of Ce:LiSrxCa1-xAlF6

The development of solid state tunable lasers in the ultraviolet region would have a wide range of applications, including atmospheric remote sensing, atmospheric spectroscopy and pollution monitoring. The first work with Ce:LiCAF was published in 1993, with subsequent reports on favorable results with Ce:LiSAF. While the original quality of Ce:LiSAF is superior, it suffers from solarization. In contrast, Ce:LiCAF shows minimal solarization and higher efficiencies, even with the typically high-scatter materials available. This presentation will summarize the crystal growth and material characterization of a series of colquiriite crystals with various Sr/Ca ratios. Based on these results, in addition to laser measurements, an optimum composition of Ce:LiSrxCa1-xAlF6 will be determined.