EXCEDE technology development IV: demonstration of polychromatic contrast in vacuum at 1.2 λ/D

This paper is the fourth in the series on the technology development for the EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) mission concept, which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept operating with a Phase Induced Amplitude Apodization (PIAA) Coronagraph and a Deformable Mirror (DM) to create a "dark-hole" or a region of high-contrast starlight suppression at the focal plane to allow direct imaging of exoplanets. This will allow fundamental science in the form of direct detection and spatial resolution of low surface brightness circumstellar debris disks, and the direct imaging of giant planets with angular separations as close in as the habitable zone of the host star. Thus, EXCEDE can function as both a scientific and technological precursor for any mission capable of imaging exo-Earths. Previously, we have reported experimental results on the first milestone, the demonstration of EXCEDE contrast in monochromatic light in air and more recently in vacuum. In this paper, we report on the procedure and the experimental results obtained for our second milestone demonstration of the EXCEDE starlight suppression system carried in a vacuum chamber at the Lockheed Martin Advanced Technology Center. This includes high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 1x10 -5 median contrast between 1.2 and 2.0 λD simultaneously with 3x10 -7 median contrast between 2 and 11 λD in 10% bandwidth polychromatic light centered at 650 nm for a single-sided dark zone. The results are stable and repeatable as demonstrated by three measurement runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames per run. We compare reduced experimental data with simulation results from modeling experimental limits.