Vida K. Castillo

Ultraviolet laser emission properties of Ce 3+ -doped LiSrAlF 6 and LiCaAlF 6

The UV laser properties of trivalent cerium-doped LiSrAlF6 (Ce:LiSAF) and LiCaAlF6 (Ce:LiCAF) are reported. The polarized absorption, emission, and excited-state absorption cross sections for both Ce:LiSAF and Ce:LiCAF were determined for the 266-nm pump and 290-nm laser emission wavelengths. The single-exponential emission lifetime was measured to be 28 ± 2 and 25 ± 2 ns for Ce:LiSAF and Ce:LiCAF, respectively. The gain was found to be highest when the probe was polarized parallel to the optical axis of the crystal, owing to the anisotropic nature of the excited-state absorption. The excited-state absorption was ascribed to a transition from the 5d orbital of Ce3+ to the conduction band of the host. Laser slope efficiencies as high as 29% and 21%, respectively, were measured for Ce:LiSAF and Ce:LiCAF when the 266-nm pulsed pump beam was polarized parallel to the optical or the c axis. These are the highest laser slope efficiencies yet observed to our knowledge for any known solid-state UV laser material. When the pump beam was polarized perpendicular to the optical axis of the crystals, the gain and the laser efficiencies dropped by as much as an order of magnitude. The magnitude of pump-induced solarization was found to be highly variable for different crystals and to have an insignificant effect on the laser performance when favorable crystals were used.

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.

Comparison of Optical, Mechanical and Thermo-Optical Properties of Oxide Polycrystalline Laser Gain Materials with Single Crystals

Comparisons of the spectroscopic, mechanical, thermo-optic, and laser performance properties between single crystal and ceramic oxide gain materials will be presented. Inaccuracies and myths regarding these ceramics will be dispelled by presentation of statistically-significant data.

Laser Studies of 8% Nd:YAG Ceramic Gain Material

We report what is believed to be the first demonstration of diode-pumped lasing from highly concentrated (8%) ceramic Nd:YAG. Fluorescence kinetics and laser experiments indicate the material’s potential for high repetition rate Q-switched laser development.

Material and laser characterization of Ce,Na:LiSrxCa1-xAIF6 compounds

Cerium has been doped in both LiCAF and LiSAF. However, each host has some intrinsic problems resulting in scatter and thermal expansion coefficient issues, respectively. In order to optimize the laser host, crystals were grown on various compositions of Ce,Na:LiSrxCa1-xAlF6. The materials produced were characterized using a variety of methods, including differential thermal analysis, glow-discharge mass spectrometery, electron microprobe, and various microscopic techniques. Samples were fabricated to characterize the absorption and emission properties for each crystal composition. Finally, laser threshold and efficiency were characterized for the various samples. Through an analysis and comparison of these critical aspects, an optimized, commercially-viable crystal can be identified to be incorporated into a tunable, solid-state UV laser system. In the case of the selected crystal system, the crystal growth characteristics of the various crystals are very similar. In the case of the selected crystal system, the crystal growth characteristics of the various crystals are very similar. Absorption and emission values for the strontium-rich compositions are greater than those for the calcium-rich compositions. Lasing was achieved in all of the samples with different output coupler transmissions. The Sr/Ca=35/65 composition showed the highest output powers. Taking into consideration all three aspects of this resaerch, there exists an intermediate composition close to Sr/Ca=35/65, that would be an optimized host as a novel UV laser host.

Q-switched laser operation of 8% ceramic Nd:YAG

We report what we believe to be the first demonstration of Q-switched, diode-pumped lasing from highly concentrated (8%) ceramic Nd:YAG. Fluorescence kinetics and laser experiments indicate the materials potential for high repetition rate operation.

Growth of low-scattering-loss Cr3+:LiSrAlF6 single crystals

The growth of high quality, low scattering loss Cr doped LiSAF single crystals by Czochralski pulling technique is described. Scattering loss as low as 0.1%/cm has achieved. The loss depends on the Cr doping concentration. We found that maintaining flat interface growth is crucial to reduce scattering loss and minimize wavefront distortion. These low loss materials provide true prospect of all solid state diode pumped tunable laser as well as ultrashort pulse generation and amplification.

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.