Phase-coherent detection of an optical dipole force by Doppler velocimetry

• Published in: Optics express Vol. 19; no. 11; pp. 10304 - 10316
• Main Authors: Biercuk, M J, Uys, H, Britton, J W, Vandevender, A P, Bollinger, J J
• Format: Journal Article
• Language: English
• Published: United States 23.05.2011
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.19.010304

We report phase-coherent Doppler detection of optical dipole forces using large ion crystals in a Penning trap. The technique is based on laser Doppler velocimetry using a cycling transition in 9Be+ near 313 nm and the center-of-mass (COM) ion motional mode. The optical dipole force is tuned to excite the COM mode, and measurements of photon arrival times synchronized with the excitation potential show oscillations with a period commensurate with the COM motional frequency. Experimental results compare well with a quantitative model for a driven harmonic oscillator. This technique permits characterization of motional modes in ion crystals; the measurement of both frequency and phase information relative to the driving force is a key enabling capability--comparable to lockin detection - providing access to a parameter that is typically not available in time-averaged measurements. This additional information facilitates discrimination of nearly degenerate motional modes.