Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna

We report on the first demonstration of time-delay interferometry (TDI) for LISA, the Laser Interferometer Space Antenna. TDI was implemented in a laboratory experiment designed to mimic the noise couplings that will occur in LISA. TDI suppressed laser frequency noise by approximately ${10}^9$ and clock phase noise by $6\times {10}^4$, recovering the intrinsic displacement noise floor of our laboratory test bed. This removal of laser frequency noise and clock phase noise in postprocessing marks the first experimental validation of the LISA measurement scheme.

Figure 1

Schematic representation of laser links between spacecraft. (a) single round-trip and (b) one-way phase measurements. (c) LISA constellation showing the six (one-way) interspacecraft phase measurements. All spacecraft are identical.

Figure 2

Schematic of one bench of the LISA interferometry test bed (the other bench is an identical copy). The benches are mechanically coupled via a vacuum envelope. $\lambda /4=\mathrm{\text{quarter wave plate}}$, $\lambda /2=\mathrm{\text{half wave plate}}$, $\mathrm{PBS}=\mathrm{\text{polarizing beam splitter}}$, $\mathrm{PM}=\mathrm{\text{proof mass}}$, $\mathrm{DAC}=\mathrm{\text{digital-to-analog converter}}$, $\mathrm{ADC}=\mathrm{\text{analog-to-digital converter}}$.

Figure 3

Recorded (i) relative clock offset and (ii) detrended clock offset (clock noise), obtained from the sideband-carrier beat note phase measurement.

Figure 4

Displacement measurements of the LISA interferometry test bed showing (i) injected laser phase noise, (iv) interpolated and clock noise corrected Sagnac TDI variable, demonstrating phase noise cancellation by $\sim 9$ orders of magnitude, down to the interferometer noise floor (v). Note: $1\mu \mathrm{cycle}\simeq 1\mathrm{pm}$ displacement equivalent.