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[en] Laser lighting systems can take many form factors for applications, such as spotlighting, general illumination, or decorative lighting. The use of lasers in conjunction with phosphors for white lighting leads to questions about incorporating the various package elements. Some practical considerations of a transmission geometry system implementing a blue laser and a yellow Ce:YAG single crystal phosphor are discussed, with specific focus on color tuning and the optical efficiency of the single crystal. A compact emitter is demonstrated with examples of modifications to increase the system performance and complexity. Moving from a cool white system to a warm white system is done through the addition of a red light such as a red laser or red phosphor. The single crystal phosphor component needs to allow light to be coupled in from the laser and has high extraction efficiency. A wavelength-selective reflective coating is implemented to address these concerns, which increases the luminous efficacy of the system. Engineering the phosphor element using this concept may allow for single crystal phosphors to be viable options for future laser lighting systems. (© 2020 Wiley‐VCH GmbH)
[en] Polarization reversal in polycrystalline ferroelectrics is shown to occur via two distinct and sequential domain reorientation steps. This reorientation sequence, which cannot be readily discriminated in the overall sample polarization, is made apparent using time-resolved high-energy x-ray diffraction. Upon application of electric fields opposite to the initial poling direction, two unique and significantly different time constants are observed. The first (faster time constant) is shown to be derived by the release of a residual stress due to initial electrical biasing and the second (slower time constant) due to the redevelopment of residual stress during further domain wall motion. A modified domain reorientation model is given that accurately describes the domain volume fraction evolution during the reversal process.