A stable foundation for cutting-edge physics
An active vibration isolating platform based on an instrument from Guralp Systems is helping to provide new insights into atomic physics.
The platform, devised by the research group of Nobel Prize winning physicist Steven Chu, relies on a vertical CMG-3 sensor to provide accurate measurements of long-period vibration.
Standard designs for isolation platforms, which rely on springs or air cushions, cannot effectively remove vibrations with a lower frequency than the natural frequency of the system. To be able to isolate an experiment from natural microseisms and vibration modes in buildings, which have frequencies in the 0.1 – 1 Hz range, a spring would have to be prohibitively large.
In this new design, the output from the sensor is used in a second feedback loop which operates an air piston to oppose the vertical motion of the platform.
Preliminary results showed vibrations in the critical range 0.1 – 1 Hz to be reduced by a factor of up to 300.
Using this vibration platform, the group has been able to make measurements of unprecedented accuracy. Local g has been measured to an accuracy of 6 × 10-11 (60 parts per trillion), enough to be able to view earth tides and ocean loading effects solely from the variation in gravitational strength.
Steven Chu’s group have also been able to measure the fine structure constant (which defines the strength of electromagnetic interaction) to a precision of 7.4 × 10-9 (7.4 parts per billion).
For more information, please see the Stanford atom interferometry group Web site.
Active Low Frequency Vertical Vibration Isolation
J. M. Hensley, A. Peters, S. Chu, Rev. Sci. Instrum., 1999, 70, 2735 (PDF at Stanford Web site)