RESUMO
When the initial size of an atom cloud in a cold atom interferometer is negligible compared to its size after free expansion, the interferometer is approximated to a point-source interferometer and is sensitive to rotational movements by introducing an additional phase shear in the interference sequence. This sensitivity on rotation enables a vertical atom-fountain interferometer to measure angular velocity in addition to gravitational acceleration, which it is conventionally used to measure. The accuracy and precision of the angular velocity measurement depends on proper extraction of frequency and phase from spatial interference patterns detected via the imaging of the atom cloud, which is usually affected by various systematic biases and noise. To improve the measurement, a pre-fitting process based on principal component analysis is applied to the recorded raw images. The contrast of interference patterns are enhanced by 7-12 dB when the processing is present, which leads to an enhancement in the precision of angular velocity measurements from 6.3 µrad/s to 3.3 µrad/s. This technique is applicable in various instruments that involve precise extraction of frequency and phase from a spatial interference pattern.
Assuntos
Aceleração , Movimento , Rotação , Diagnóstico por ImagemRESUMO
The effective double-site metal ion replacement strategy was adopted to optimize the crystal field environment of a Mn4+-activated fluoride phosphor. In this study, a series of K2yBa1-ySi1-xGexF6:Mn4+ phosphors with optimized fluorescence intensity, excellent water resistance, and outstanding thermal stability was synthesized. The composition adjustment includes two different types of ion substitution based on the BaSiF6:Mn4+ red phosphor: [Ge4+ â Si4+] and [K+ â Ba2+]. X-ray diffraction and theoretical analysis revealed that Ge4+ and K+ could be successfully introduced into BaSiF6:Mn4+ to form new solid solution K2yBa1-ySi1-xGexF6:Mn4+ phosphors. The emission intensity enhancement and slight wavelength shift were detected in different cation replacement procedures. Furthermore, K0.6Ba0.7Si0.5Ge0.5F6:Mn4+ with superior color stability performance possessed a negative thermal quenching phenomenon. Excellent water resistance was also found, which was more reliable than K2SiF6:Mn4+ commercial phosphor. A warm WLED with low correlated color temperature (CCT = 4000 K) and high color rendering index (Ra = 90.6) was successfully packaged by using K0.6Ba0.7Si0.5Ge0.5F6:Mn4+ as the red light component, and it also exhibited high stability for different currents. These findings demonstrate that the effective double-site metal ion replacement strategy can open up a new avenue for designing new Mn4+-doped fluoride phosphors to improve the optical properties of WLEDs.
RESUMO
In an atomic fountain, atoms in motion can be spatially separated into discrete Zeeman sub-states by magnetically induced Stern-Gerlach effect. With resonant light pulses acting as a shutter, specific states are selected for subsequent experiments. Such separation-selection process in atomic optics is the analogue of a spatial filter in physical optics which selects and purifies the modes of light. This technique is demonstrated by injecting a pulsed current in a circular coil around a vertical atomic fountain, separating the pre-cooled Rubidium atoms by a distance of centimeters in between, and filtering each single sub-state with block pulses. The filtered atoms after the process is highly purified in the desired sub-state. The apparatus of the atomic spatial filter is adaptable in atomic optics and can be integrated into the high-vacuum chamber of an atomic fountain.
