  Laser frequency noise suppression is a critical requirement for the Laser
Interferometer Space Antenna (LISA) mission to detect gravitational waves. The
baseline laser stabilization is achieved using cavity pre-stabilization and a
post-processing technique called Time-Delay-Interferometry (TDI). To enhance
the margins for TDI, alternate laser locking schemes should be investigated. A
novel stabilisation blending the excellent stability of the arm with the
existing cavity reference has been shown theoretically to meet the
first-generation TDI margins. This locking system was designed to be
implemented as a firmware change and have minimal or no changes to the LISA
hardware. This paper experimentally verifies the hybrid laser locking technique
by utilizing two references - an optical cavity, and an interferometer with
delay imparted using 10 km of optical fiber. The results indicate the viability
of the combination of arm-cavity locking system for LISA. They show the key
benefits envisioned by this technique; suppression of the cavity fluctuations
by the arm sensor (by 21 dB in this demonstration) and reduction of Doppler
pulling of the laser frequency, a key technical challenge for arm locking.
