Fundamental investigations in orientation control process for anisotropic laser ceramics

Abstract

We present theoretical studies on the orientation control of micro‐domains in anisotropic laser ceramics. The direction of the crystal axis that is parallel to easy magnetization in each micro‐domain can be aligned along the direction of the applied magnetic field via two steps of fabrication processes. In the first step the alignment is performed during the slip‐casting under the magnetic field, where directions of primary particles are forced to align along the direction of easy magnetization. However, even though rare‐earth trivalent ions doped into primary particles as luminous ions enhance their magnetic moment, the perfect alignment control is not always possible due to Brownian fluctuations by slurry solvent at this stage. The further orientation control can be processed by the preferential grain growth, where an adequate orientation distribution of primary articles in the casted green body is required for the nearly perfect alignment in sintered ceramics. Therefore, it is important for further improvements of anisotropic laser ceramics to find the orientation distribution of primary particles in the slurry, which is determined by the ratio between the anisotropic magnetic potential and the thermal fluctuations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Process design of microdomains with quantum mechanics for giant pulse lasers

“…Considering Kramers’ degeneracy, the second-order perturbation of the Zeeman effect gives M along the direction of B in one Yb 3+ by 20 where g J , m B , k , f i and < j | A | i > are the Lande g-factor, Bohr magneton, Boltzmann constant, Boltzmann factor for level i and matrix element of an operator A between i and j states, respectively. Without any crystal field, Equation ( 3 ) simplifies to the Curie law, which indicates that doping with Yb 3+ forms Δχ .…”

“…To limit the intensity of the applied magnetic field to the maximum that traditional electromagnets can generate (1.4 T), we enhanced Δχ by doping with RE 3+ , because Δχ of N times enables reduction of B by 1/ N 0.5 times 20 . Figure 2 shows the calculated and experimental values for Δχ induced by Yb 3+ doping for several anisotropic laser host crystals.…”

“…Equation ( 4 ) reveals that we can realize < θ > of at least 21.6° when δ is 300 nm. If only the orientation of microcrystals with δ larger than 1.0 μm occurs because of preferential grain growth based on Ostwald ripening 20 , we can expect that < θ > is smaller than 5.8°.…”

“…Consequently, n m and n s are 1.622 and 1.620, respectively 23 . F ( θ ) can be derived from Equation ( 1 ) as where Erfi(z) gives the imaginary error function, and B min is a parameter that indicates the lower limit of the magnetic flux density for orientation control 20 . B min is proportional to the square root of RE 3+ concentration.…”

Synthesis and Magnetic Characterization of SolGel‐Derived Submicrometer NaGd(WO4)2

“…The paramagnetic nature of the synthesized NGW powders leads to orient the particles under magnetic field, but the magnetic field required for orientation depends on particle size, size distribution, and particle dispersion. Compared to earlier reports of tetragonal YVO 4, it is necessary to apply nearly 50 kOe magnetic field to orient the NGW particles. Doping of magnetically active rare earth ions such as Pr 3+ , Ho 3+ , Dy 3+ , and Er 3+ in NGW matrix may reduce the required magnetic field strength and improve the laser output from the system…”