  We summarize the current best polychromatic (10 to 20 % bandwidth) contrast
performance demonstrated in the laboratory by different starlight suppression
approaches and systems designed to directly characterize exoplanets around
nearby stars. We present results obtained by internal coronagraph and external
starshade experimental testbeds using entrance apertures equivalent to off-axis
or on-axis telescopes, either monolithic or segmented. For a given angular
separation and spectral bandwidth, the performance of each starlight
suppression system is characterized by the values of raw contrast (before image
processing), off-axis (exoplanet) core throughput, and post-calibration
contrast (the final 1 sigma detection limit of off-axis point sources, after
image processing). To place the current laboratory results in the perspective
of the future Habitable Worlds Observatory (HWO) mission, we simulate visible
observations of a fiducial Earth/Sun twin system at 12 pc, assuming a 6m
(inscribed diameter) collecting aperture and a realistic end-to-end optical
throughput. The exposure times required for broadband exoearth detection (20%
bandwidth around a wavelength of 0.55 microns) and visible spectroscopic
observations (R=70) are then computed assuming various levels of starlight
suppression performance, including the values currently demonstrated in the
laboratory. Using spectroscopic exposure time as a simple metric, our results
point to key starlight suppression system design performance improvements and
trades to be conducted in support of HWO exoplanet science capabilities. These
trades may be explored via numerical studies, lab experiments, as well as high
contrast space-based observations and demonstrations.
