Ceramic laser gain materials have been in development since the 1960's but it was not until the
resurgence in research and development in the 1990's that they showcased equivalent laser performance
to their single crystal counterparts. Ceramics offer numerous distinctive advantages over single crystal
and are considered to be the key enabler in power scaling of solid state lasers. Ceramics can be made
larger, at lower cost, and with additional degrees of engineering design freedom than single crystals, such
as higher doping concentration, more uniform or tailored distribution of dopants, and feasibility to be
fabricated into monolithic composite structures without bonding. At Raytheon, powder processing
methodology has matured to meet the optical requirement, scale-up challenge, and laser performance
characteristics in Yb, Nd, and Er doped ceramic YAG materials. This communication presents the latest
results obtained by Raytheon on the US fabricated ceramic laser materials.
Optical quality ceramic Yttrium Aluminum Garnet (YAG, Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>) materials for high power solid state lasers are being developed at Raytheon. The remaining challenge for ceramic gain materials is elimination of residual absorption and scattering centers. At Raytheon, significant progress has been achieved in the optical quality improvement, scale-up, and demonstration of laser quality Yb, Nd, and Er doped ceramic YAG materials. This communication presents Raytheon's current development status in ceramic YAG fabrication and doped ceramic YAG material characteristics.
Polycrystalline Yttrium Aluminum Garnet (YAG) is being considered as an attractive material candidate for IR transparent missile domes and reconnaissance windows, due to its superior optical clarity and mechanical properties compared to the incumbent material choices. YAG possesses a very uniform index of refraction with minimal variation. Its fracture strength, hardness, and toughness also rank high among various other optically transparent materials and can be optimized further through grain size minimization. Polycrystalline YAG has been in development for several years at Raytheon for laser gain and IR transparency applications. Recent advances in optical loss characterization and optimization, scale-up efforts, and the fabrication of non-planar geometries such as hemispherical domes will be presented. In addition, the YAG material trade study conducted to date on thermal, optical, mechanical properties are discussed.
High optical quality polycrystalline yttrium aluminum garnet (YAG) is now available. The optical
properties of pure polycrystalline YAG and 1% Nd doped polycrystalline YAG are reported from the
midwave infrared to the visible. The absorption and scatter properties are represented in terms of standard
An efficient microchip laser utilizing domestically fabricated ceramic Yb:YAG is presented. In continuous-wave
(cw) and Q-switched operation, the laser maintains linear polarization with 22 dB extinction and oscillates in the
fundamental TEM<sub>00</sub> mode. In cw mode, the ceramic laser has an output power of 2.25 W and a slope efficiency of 66%.
When passively Q-switched at 11.4 kHz repetition rate using Cr:YAG, the 1.9 ns pulse has an average power of 0.72 W
and a slope efficiency of 46%. To our knowledge, this is currently the highest reported power from a ceramic Yb:YAG
laser. The laser performance of the 5-at.% ceramic is compared to a 10-at.% single crystal, and we discuss how the
scattering loss and storage efficiency of the ceramic medium affect its laser characteristics.
Optical quality polycrystalline yttrium aluminum garnet (YAG) materials suitable for laser gain application have been under development at Raytheon Advanced Materials Laboratory since late 2003. Significant progress has been achieved in the optical quality improvement, scale-up, Yb and Nd dopant incorporation, and various characterizations. This communication discusses Raytheon's ongoing developments in laser quality ceramic YAG fabrication and its characteristics in comparison to the current state of the art ceramic YAG made by Konoshima Chemical in Japan.
With the ever increasing demands for optical quality YAG, ceramic laser gain materials present attractive advantages in design, fabrication, and cost without any penalty in performance compared to their single crystal counterparts. Due to intrinsic differences in the production method, ceramic gain media can be fabricated faster, larger, more affordably, and at higher and more uniform doping. This investigation into polycrystalline YAG included optical, mechanical, and microstructural characterization -- focusing primarily on Konoshima Chemical Company ceramic YAG, the current global state of the art.