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A two-frequency acousto-optic modulator driver to improve the beam pointing stability during intensity ramps

B. Fröhlich·T. Lahaye·B. Kaltenhäuser·H. Kübler·S. Müller·T. Koch·M. Fattori·T. Pfau
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Abstract

We report on a scheme to improve the pointing stability of the first order beam diffracted by an acousto-optic modulator (AOM). Due to thermal effects inside the crystal, the angular position of the beam can change by as much as 1 mrad when the radio-frequency power in the AOM is reduced to decrease the first order beam intensity. This is done for example to perform forced evaporative cooling in ultracold atom experiments using far-off-resonant optical traps. We solve this problem by driving the AOM with two radio-frequencies $f_1$ and $f_2$. The power of $f_2$ is adjusted relative to the power of $f_1$ to keep the total power constant. Using this, the beam displacement is decreased by a factor of twenty. The method is simple to implement in existing experimental setups, without any modification of the optics.

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B. Fröhlich, T. Lahaye, B. Kaltenhäuser, H. Kübler, S. Müller, T. Koch, M. Fattori, T. Pfau. 2007-01-16. A two-frequency acousto-optic modulator driver to improve the beam pointing stability during intensity ramps. https://doi.org/10.1063/1.2720725

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