The cold atom interferometer (CAI) is a high-precision inertial measurement instrument with wide-ranging applications. Identifying its error sources and enhancing its precision are critical for further improving its performance. This work identifies a phase shift in Raman lasers induced by the tapered amplifier (TA) and analyzes its subsequent effect on the atom interferometer measurements. We discover a periodic oscillation of this phase with linear variation of the TA temperature. A theoretical model is built to describe this phase shift in the context of the gain medium with a Fabry–Pérot effect. A method is proposed to measure the amplitude of the phase oscillation, which is insensitive to the drift of the measured phase. TA-induced phases under different TA parameters are then measured and their influence on a typical atom gravimeter is evaluated. Based on typical parameters, the estimated gravity measurement noise induced by the TA is 0.39 μ Gal.
The cold atom interferometer (CAI) is a high-precision inertial measurement instrument with wide-ranging applications. Identifying its error sources and enhancing its precision are critical for further improving its performance. This work identifies a phase shift in Raman lasers induced by the tapered amplifier (TA) and analyzes its subsequent effect on the atom interferometer measurements. We discover a periodic oscillation of this phase with linear variation of the TA temperature. A theoretical model is built to describe this phase shift in the context of the gain medium with a Fabry–Pérot effect. A method is proposed to measure the amplitude of the phase oscillation, which is insensitive to the drift of the measured phase. TA-induced phases under different TA parameters are then measured and their influence on a typical atom gravimeter is evaluated. Based on typical parameters, the estimated gravity measurement noise induced by the TA is 0.39 μ Gal.
Stimulated Raman transitions are often used in an atom interferometer (AI) for wave packet manipulation. Normally, two lasers with different frequencies contained in a Raman beam are combined first and then amplified by a single tapered amplifier (TA). This configuration can simplify the laser system of the AI, however, additional sidebands will be generated by the TA because of the nonlinear effect in the TA. In this work, the impact of additional sidebands generated with a single TA on the AI is studied. We first observe the additional sidebands in a Raman laser by a Fabry-Pérot interferometer (FPI), and the additional sidebands will be greatly suppressed by reducing the injection laser power of the TA. This is also confirmed by observing the position-dependent Raman transitions induced by additional sidebands at different injection power in an AI. However, the phase shifts induced by additional sidebands are not reduced obviously when the injection power of the TA is reduced. Therefore, it is necessary to separately amplify two lasers contained in the Raman laser by two TAs for a high precision AI. The spectroscopy of Raman laser generated by two TAs is also measured by the FPI, and the impact of additional sidebands on the AI is eliminated. This work has guiding significance for the design of the laser system in a high-precision AI.
Simultaneous two-frequency amplification is highly desirable in cold atom experiments. The nonlinear response would appear in the two-frequency amplification with a semiconductor tapered amplifier (TA) and has a direct influence on the experimental result. We investigated in detail the effects of frequency difference, total power, and power ratio of two seeding lasers on the output components based on a simplified theoretical model. The simulation results showed that the multiple sideband generation in the amplifier due to self-phase and amplitude modulation could be suppressed and the TA tended to linearly amplify the power ratio between two-frequency components, when the two seeding lasers had a large frequency difference. This was verified experimentally in the output power ratio measurement via a calibrated Fabry–Perot interferometer method with a good linearity and an uncertainty of 1%. We also discussed the consequences of power ratio responses in the amplification in light of cold atom experiments, especially in the ac Stark shift related phase error of Raman-type atom interferometers (AIs). It was shown that the fluctuation of intensity ratio of Raman beams may induce significant systematic errors for an AI gyroscope.
We present the investigation on the frequency-dependent amplification (FDA) of a tapered amplifier (TA) and the corresponding influence on Raman-type atom interferometers. In our interferometer, the output of two phase-locked diode lasers is injected into a TA to generate Raman beams. The frequency of one laser is chirped during the interfering process, which induces a variance of the Raman lasers power as a result of the FDA of the TA. The corresponding power ratio variation of the Raman lasers is measured by beat note method, which shows a linear dependence with a slope of -0.087(4)/GHz when the laser frequency changes over 2 GHz at 780 nm. The corresponding error related to AC Stark effect due to this frequency-dependent variation is estimated for our atom interferometer. The investigation presented here may provide hints for other experiments involving TAs.
Summary form only given. Atom interferometry based on cold atoms and light beamsplitters is a mature technique, which allows for the realization of highly sensitive inertial sensors. In the most advanced inertial sensors based on atom interferometry, atomic wavepackets are manipulated by light beamsplitters using two-photon Raman transitions. The interferometer phase shift, which depends on the acceleration and the rotation of the experimental setup with respect to the inertial reference frame defined by the atoms in free fall, is derived from the relative displacement of the atoms with respect to the beamsplitter laser's equiphases. Wavefront aberrations thus induce parasitic phase shifts, which bias the measurement, and which are linked to the residual ballistic motion of the atoms across the laser beam profile during their free fall and cancels out at zero atomic temperature. The wavefront distortions of the lasers beamsplitters is an important limit in the accuracy of atom interferometers and in particular, the dominating contribution in best cold atom gravimeters (CAG) uncertainty budget. This work clears the way towards unprecedented accuracies for absolute gravimetry, below the 1 μGal level. The method proposed can be applied to any atomic sensor based on light beamsplitters, which are inevitably affected by distortions of the lasers wavefronts. The improved control of systematics it provides will have significant impact in high precision measurements with atom interferometry, with important applications to geodesy, fundamental physics tests and to the development of highest grade inertial sensors.
Cold-atom interferometer based on stimulated Raman transition is interesting for both fundamental researches and precision measurements. Measuring g, the free fall acceleration, plays an important role in these applications. We describe the theory of atom interferometry, including the evolution of the atomic wavepacket in gravity field, the laser-atom interaction, and the interference of the atomic waves. In this article, we introduce the procedure of measuring g using atom interferometer, the experimental setup, and the tendency of the future development. The works of the domestic and international groups for g measurement are concluded. Furthermore, the noise limits and dominant systematic effects in atom gravimeters are analyzed. The suppressions of the background vibration, the Raman phase noise, and the evaluation of the main systematic effects, are introduced. Finally, the other applications using the atom interferometers for precision measurement are presented, such as in measuring the Newton’s gravitational constant, in testing the weak equivalence principle and the other fundamental applications in physics studies.
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.