Cross-aperture nulling interferometry

The Polychromatic Reflective Testbed (PoRT) at the ET Lab is a testbed for demonstrating and characterizing cross-aperture nulling interferometry instrument concepts. The ET lab currently focuses on two types of cross-aperture nullers, the Vortex Fiber Nuller and the Photonic Lantern Nuller.

Vortex Fiber Nuller (VFN)

Fiber nulling as a means to detect and characterize exoplanets and circumstellar disks at or within the diffraction limit was first introduced and demonstrated by Haguenauer and Serabyn (2006). This concept is largely based on the Bracewell nulling interferometer (Bracewell and MacPhie, 1979). The first fiber nuller was demonstrated on sky at Palomar observatory by Hanot et al. (2011). We recently introduced the concept of vortex fiber nulling, which circumvents the need of a rotating baseline and greatly simplifies the design and operation of the fiber nuller (Ruane et al., 2018). The VFN concept was demonstrated in the ET Lab and on-sky at the Keck II telescope (Echeverri et al. 2019, Echeverri et al. 2023). The combination of VFN starlight suppression at the 1E-3 raw contrast level (limited by AO residuals and finite stellar size) and high-resolution spectroscopy will enable the detection and high-resolution spectroscopic characterization of planets at or within the diffraction limit (down to ~10 mas on TMT). Using the latest giant planet occurrence rates from Nielsen et al. (2019), we predict the discovery and simultaneous characterization of dozens of new young giant planets in nearby young associations and star forming regions with Keck, and even more with TMT. Benefiting from the giant aperture and angular resolution of TMT, Ruane et al. (2018) predicts the detection of nearby Earth-size planet Ross 128 b in reflected light in 30 hours. Less challenging configurations, which include giant planet, mini-Neptunes and super-Earths will also be accessible. The challenging case of temperate Earth-size planets in less favorable configurations than Ross 128 b (e.g. more distant) will require the extreme adaptive optics system of the TMT-Planetary Systems Imager.

Photonic Lantern Nuller (PLN)

The PLN is based on the VFN concept, but uses a mode-selective photonic lantern to destructively interfere the starlight while retaining planet light at near the diffraction limit (Xin et al. 2022). It has four nulled ports through which planet light can couple, increasing the overall planet throughput through the instrument relative to the VFN. The ports also have spatially-varying coupling patterns that helps constrain the planet's location and flux ratio. Work is ongoing to characterize the properties of the PLN in the lab in monochromatic and broadband light, and to demonstrate wavefront control through the PLN.