Atom interferometry is an advanced optical manipulation tool of atoms in precision measurement field. Wavefront aberrations of the Raman beam have become one of the major obstacles impeding the improvement of measurement accuracy. Beforehand measurement of laser wavefront is impractical due to the further wavefront deterioration during optical mounting. In this work, we present a general method for evaluating the effective Raman wavefront that atoms experience and the corresponding phase shift of interferometric fringes. The method extracts the effective Zernike polynomial terms and reconstructs the wavefront using optimal estimation theory. The evaluation accuracy and convergence speed are discussed by simulation. The results predict the method adaptability and provide strong support on analytical and numerical reference for wavefront error compensation.
KEYWORDS: Magnetism, Chemical species, Gyroscopes, Polarization, Time metrology, Xenon, Rubidium, Signal to noise ratio, Signal detection, Signal processing
In a nuclear-magnetic-resonance gyroscope (NMRG), the polarization of nuclear spins and the detection of motional
information are usually achieved by utilizing the atomic spins of alkali atoms. The parameters of the atomic spins are
mainly evaluated by the relaxation time. Relaxation time is very important and can influence signal-to-noise ratio,
dynamic range, start time, and other gyroscope parameters. Therefore, its accurate measurement is critical in the study of
NMRG performance. In this study, we evaluate a variety of methods to measure the transverse and longitudinal
relaxation times. First we examine the free-induction-decay method, which is the industry standard for measuring spin
relaxation time. Second we investigate the improved free-induction-decay, fitting-ratio, and magnetic-resonance-broadening-
fitting methods for measuring the transverse relaxation time, and the flipped polarization method for
measuring the longitudinal relaxation time. By changing the experimental conditions, we obtain the longitudinal
relaxation time using the flipped polarization method under a variety of conditions. Finally, by comparing these
measurement methods, we propose the best measurement methods under different conditions.
Non-planar ring resonators are widely used for high precision ring laser gyroscopes
including Zero-Lock Laser Gyroscopes. The analysis of optical-axis perturbation in nonplanar ring
resonators is important for resonator design. Ray matrix approach based on appropriate coordinate
systems has been employed to analyze the optical-axis perturbation in nonplanar ring resonators. The
sensitivities of optical-axis decentration (SD) and optical-axis tilt (ST) in nonplanar resonators with 90°
and 270° image rotation are discussed in detail in the region of 0< K <8, where K is the ratio of the total
cavity length to the radius of the curvature mirrors. There are both four singular points in the whole
region of 0<K<8. On the left of the first singularity, it is found that the longer the mirror radius, the less
the optical-axis decentration sensitivity. This is opposite the behavior of planar ring resonators, but the
behaviors of optical-axis tilt sensitivity in planar and nonplanar ring resonators are similar. In planar
resonators, it also demonstrates that in the region of 0<K<2, larger the mirror radius is, higher
sensitivity of optical-axis decentration will be, but lower sensitivity of optical-axis tilt will be. These
results are confirmed by related experiments. It is worth to note that SD and ST in the nonplanar
resonator with certain parameters have the similar singularities. The analysis in this paper is important
for the resonator design, improvement and beam position control nonplanar ring resonators.
A generalized model for beam-path variation analyzed with vector method in square ring
resonators is established. The model can be applied to analyze beam-path variation in various ring
resonators induced by all the possible perturbation sources. The generalized model is useful for the
cavity design, cavity improvement, alignment of planar ring resonators and research on backscattering
coupling effect. Backscattering coupling effect in square ring resonator has been chosen as examples to
show its application. Backscattering coupling coefficient r is obtained as a function of mirror's axial
displacements. Some novel results of backscattering coupling effect have been acquired. The results
indicate that r can not be reduced to zero because of the initial machining errors of surfaces of plane
mirrors. However, r can be reduced to zero almost when stabilizing frequency of laser gyro by take the
suitable values of axial displacements of plane mirrors. These results are important for high precision
laser gyro.
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