The missing link: development of the frequency acquisition system for LISA (MSc thesis)
Job Offer from January 10, 2020
LISA (Laser Interferometer Space Antenna) is an ambitious space mission currently under development. It aims to listen to gravitational-wave sources which are only audible from space and which promise plenty of exciting new science. The mission consists of three spacecraft forming a triangle with 2.5 million km (~7 times the earth-moon distance) arm length. Laser interferometry will be used to measure the distances between test masses on board the spacecraft with picometer precision. This will ultimately enable the detection of gravitational waves which would slightly change these distances.
However, before scientific measurements can take place, the laser links for the interferometers have to be established. To achieve that, satellite thrusters and telescopes need to be adjusted so that the laser light sent from each satellite actually reaches its counterpart.
The sophisticated procedure to establish all six one-way links is called the constellation acquisition. It includes not only the aforementioned spatial adjustments, but also the tuning of the different laser frequencies: for the LISA interferometry, a maximum of 25 MHz is allowed when measuring the difference in individual frequencies. These frequencies cannot be set beforehand with the required precision, hence they must be tuned in the overall acquisition procedure. The described frequency acquisition will primarily be performed by the core piece of LISA's metrology chain, the phasemeter, whose main tasks is the extraction of the interferometric phases (and hence the scientific signals).
This project focuses on the implementation of the frequency acquisition system for the LISA phasemeter. The core pieces of the latter will be hosted on an FPGA, hence the main activities in this project will be based on FPGA designing/programming (mostly in VHDL).
Detailed tasks would be:
- Setting up an environment for development and testing of the frequency acquisition (targeted hardware platform: STEMlab board featuring a ZC7010 SoC [System-on-chip])
- Implementation and testing of FPGA-designs featuring:
- an FFT for frequency analysis
- a peak finder
- a state machine to manage the acquisition procedure
- feedback loops for laser frequency/phase control
- feedback loops for gain adjustments
- (Optional) Utilize the test environment to analyze the main phase extraction of the phasemeter (a phase-locked loop [PLL]) for non-linearities in an absolute digital test
Experience in FPGA programming and digital signal processing (DSP) would be beneficial, but not strictly necessary.
Please contact Dr. Thomas Schwarze for further information.