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Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Optical Metrology

Tunable frequency reference for LISA

S. Amairi Pyka, K. Döringshoff, E. Kovalchuk, K. Möhle, A. Peters

The optical read out of the LISA interferometer arms requires a high frequency stability of the used Nd:Yag lasers. A change in the laser frequency would give a signal equivalent to a change in the length of the interferometer arms covering the signal of a gravitational wave.
To achieve the desired sensitivity a laser stability of 6x10-6 Hz/Hz1/2 is required. This is to be attained in three steps of stabilization. The first step is to lock the frequency of each laser in the system to a Fabry-Perot cavity using a locking scheme known as Pound-Drever-Hall scheme. In this prestabilization a stability of 30 Hz/Hz1/2 should be achieved. The next level is obtained by stabilizing the laser frequency to one or more of the long LISA arms. The remaining few orders of magnitude cannot be achieved by active stabilization, but only by post processing the data with a technique called "time-delay interferometry".



LISA Requirements


In addition to the stability requirements, the yearly variation of the triangular satellite configuration, causing slow Doppler- shifts, leads to the demand of a tunable prestabilization. These two requirements, high stability and tunability, are not yet realized within an optical cavity.
With the condition not to use an EOM or AOM for offset locking the first approach would be to test the stability of a cavity with one mirror not directly attached to the spacer, but over a piezo-electric actuator.
The frequency stability of the laser, stabilized to this cavity will show how the mechanical properties of the piezo material will influence the stability of the modified cavity setup. We intend to test different piezo materials, especially a new piezo-electric glass-ceramic in this setup.

In further steps the implementation of other tunable frequency reference setups like for example an unequal arm length interferometer is planed.







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