Atomic gravimeter based on atom interferometry has become a hotspot of quantum optics applications in recent years and shown rapid progress in static-scene measurements. Improving the adaptability on dynamic scenes is an important development direction, which calls for in-depth research on various errors caused by carrier motions. This work focuses on the error evaluation and compensation of motion-induced misalignment between the Raman laser beam and the atomic trajectory. A theoretical analysis framework is formed to investigate the atom-laser misalignment errors by considering both the inhomogeneous Raman laser intensity and wavefront phase distributions in a dynamic perspective. The influence on fringe contrast and phase shift in an atom-interferometry gravimeter is discussed. Quantitative study has been done with different motion types, motion rates as well as random motion noises. The results show oscillational decay trends of fringe contrast with the motion amplitude and the increased significance of rotationally antisymmetric Zernike terms in dynamical Raman wavefront phase shift evaluation. Strong correlations can be found between the misalignment errors and the experimental parameters. A compensation method is proposed accordingly via quickly adjusting the Raman intensity or pulse duration and comprehensive Raman wavefront characterization. Both amplitude and phase corrections are achieved. The analytical approach and results provide a practical solution for further advances of atom-interferometry under harsh motional conditions.
Mode instability phenomenon acts as a common feature in single-frequency fiber ring lasers. Pump power and cavity length are two important control parameters affecting the output SLM stability. In this work, mode instability of an EDFRL has been experimentally investigated by utilizing two effective methods. On the whole, a mode stability map of the EDFRL scaled by pump coefficient is measured and discussed completely through the interferometer scheme, which helps to evaluate the mode stability dependent on pump power in a form of global visualization. Besides, real-time and detailed detection of various mode instability behaviors, including occasional mode hopping, periodic mode hopping and intermittent MLM oscillation, is carried out using the optical heterodyne scheme. The dynamics of mode instability can also be visualized by on-line time-frequency diagrams. This work will contribute to the analysis, understanding and suppression of mode hopping in fiber ring lasers.
Chaotic fiber ring lasers (CFRLs) can be regarded as a type of complex multi-longitudinal-mode (MLM) lasers in optical frequency domain. However, most experimental investigations on laser chaos generation are only restricted to measurements of total intensity dynamics, with frequency-domain longitudinal mode information neglected. In this work, we experimentally study the longitudinal mode dynamics of a CFRL with pump modulation by utilizing a heterodyne detection scheme, in which a beat signal between the chaotic laser and a reference laser is generated. High-resolution instantaneous emission spectra reflecting the fine longitudinal-mode structure of the CFRL in overall are measured through heterodyne detection. Besides, longitudinal mode frequency and intensity dynamics of the CFRL are monitored simultaneously via time-frequency analysis and discussed in detail. Experimental results show that the CFRL exhibits dense and irregular MLM oscillation all the time when operating at intensity chaos state. Meanwhile, each oscillating longitudinal mode in the CFRL is broadened in spectral line due to pump modulation, and can perform chaotic or random-like behaviors in mode intensity. This work will play a significant role in the further analysis, understanding and application of chaotic fiber ring lasers.
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.
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