Laser frequency stabilization by dual arm locking for LISA

Abstract

The Laser Interferometer Space Antenna (LISA) will be the first dedicated space based gravitational wave detector. LISA will consist of a triangular formation of spacecraft, forming an interferometer with 5 Â 10 6 km long arms. Annual length variations of the interferometer arms prevent exact laser frequency noise cancellation. Despite prestabilization to an optical cavity the expected frequency noise is many orders of magnitude larger than the required levels. Arm locking is a feedback control method that will further stabilize the laser frequency by referencing it to the 5 Â 10 6 km arms. Although the original arm locking scheme produced a substantial noise reduction, the technique suffered from slowly decaying startup transients and excess noise at harmonic frequencies of the inverse round-trip time. Dual arm locking, presented here, improves on the original scheme by combining information from two interferometer arms for feedback control. Compared to conventional arm locking, dual arm locking exhibits significantly reduced start-up transients, no noise amplification at frequencies within the LISA signal band, and more than 50 fold improvement in noise suppression at low frequencies. In this article we present a detailed analysis of the dual arm locking control system and present simulation results showing a noise reduction of 10 000 at a frequency of 10 mHz.

Arm locking for space-based laser interferometry gravitational wave observatories

“…However, the gain was still limited by the shallow roll off. By exploiting the pathlength mismatch between two long arms, dual arm locking uses both sensor signals to push the first sensor null to above the LISA frequency band and therefore achieves an almost flat response at low frequencies [23]. This flat response allows to increase the gain at lower frequencies much faster and significantly improve the performance of arm locking.…”

Arm locking for the Laser Interferometer Space Antenna

“…The basic concept of arm-locking is to use the information contained in the phasemeter signals to estimate the phase/frequency noise of the master laser and thereby correct it. This concept was first proposed by Sheard, et al [ 10] and has subsequently been further refined and studied by others [11][12][13][14][15][16][17]. In this work, we apply the techniques of classical optimal control theory to this problem.…”

“…Several methods of frequency stabilization have been proposed, including traditional laboratory techniques such as spectroscopic references [8] and high-finesse optical cavities [9]. Here we consider a technique known as arm-locking [10][11][12][13][14][15][16][17], which uses the arms of the LISA constellation as a frequency reference. The basic concept of arm-locking is to use the information contained in the phasemeter signals to estimate the phase/frequency noise of the master laser and thereby correct it.…”

An Overview of the Laser Interferometer Space Antenna

“…There have since been several simulated (Sylvestre 2004) and experimental (Marín et al 2005;Sheard, Gray & McClelland 2006; validations of the control system stability and noise suppression. More recently, the arm-locking control system was expanded to include signals from both arms, resulting in substantial improvement in laser frequency noise (Herz 2005;Sutton & Shaddock 2008). The remaining laser frequency noise will be removed in post-processing using a technique called time delay interferometry (TDI) (Tinto & Armstrong 1999;Tinto et al 2003).…”