New Methods for the Detection and Characterization of Exoplanets

Advancements in detection technologies have allowed the discovery of thousands of exoplanets. These discoveries have revolutionized our understanding of the Universe; not only are planets ubiquitous, but the planetary systems they populate are as diverse as the complex processes that govern their formation allow. This thesis compiles several studies on the development and application of exoplanet detection and characterization methods, in particular for direct imaging and spectroscopy. From all the planets discovered to date, only a marginal portion have been imaged. This is due to the limited access of high contrast instruments into the parameter space where most exoplanets habitate. Developments in high contrast are key to reaching a full understanding of the exoplanet population. In particular, direct methods allow for an effective characterization of the atmospheric compositions, making it possible to probe exoplanet atmospheres in search of biosignatures. A sure pathway to enhance exoplanet characterization capabilities is by taking full advantage of synergies between detection methods. In Chapter 2 these synergies are explored in the context of ε Eridani's elusive companion: three different methods are combined to constrain its mass and orbital parameters. Combining astrometry, radial velocity, and direct imaging data offers a complementarity that enhances the overall constraining power. In Chapter 3, the α Centauri system is reviewed regarding the possibility of imaging an exoplanet with the JWST observatory in the infrared. The following chapters deal with technological development for high contrast imaging and spectroscopy instruments. In Chapter 4 a coronagraph design study is presented in which new design tools are discussed and evaluated, demonstrating better coronagraph performance. In this chapter the case study is the Nancy Grace Roman Space Telescope Coronagraph Instrument, in which its heavily obstructed pupil constitutes a huge challenge for coronagraph design. Along the same lines, Chapter 5 presents the technology demonstration of the apodized vortex coronagraph (AVC). The AVC is a coronagraph concept that effectively deals with the telescope pupil discontinuities. Chapters 6 and 7 introduce a novel wavefront sensing and control algorithm for the high contrast concept of a fiber injection unit in the image plane of a coronagraph. A single mode fiber (SMF) is placed in the position of the planet to extract its light and feed it into a spectrograph. Our algorithm leverages the synergies of the coronagraph and the mode selectivity of the SMF to maximize the signal-to-noise ratio of the planet.</p

Wavefront control experiments with a single mode fiber at the High-Contrast Spectroscopy Testbed for Segmented Telescopes (HCST)

Achieving high levels of contrast over broad bandwidths with segmented aperture telescopes is a key requirement to maximize the scientific yield for future exoplanet imaging missions and ground-based extremely large telescopes. The High-Contrast Spectroscopy Testbed for Segmented Telescopes (HCST) in the Exoplanet Technology Laboratory (ET Lab) at Caltech is designed to proof test new technologies aimed at tackling some of the most pressing and challenging goals of exoplanet science, namely the imaging and spectroscopic characterization of small planets across a wide range of stellar host types, including temperature Earth-size planets. Here we report on the status of a key milestone: Demonstration of 20% bandwidth nulling experiments using single mode fibers wavefront control

Demonstration of a speckle nulling algorithm and Kalman filter estimator with a fiber injection unit for observing exoplanets with high-dispersion coronagraphy

High-dispersion coronagraphy (HDC) combines high contrast imaging techniques with high spectral resolution spectroscopy to observe exoplanets and determine characteristics such as chemical composition, temperature, and rotational velocities. It has been demonstrated in lab that with monochromatic light, a fiber injection unit (FIU), in which an optical fiber is used to couple to light from the exoplanet, could be used to direct exoplanet light to a high-resolution spectrograph, with robust performance and speckle suppression that exceeds conventional image-based speckle nulling. We now demonstrate in lab a FIU based speckle nulling scheme with a Kalman filter estimator. We currently find that speckle nulling with a Kalman filter is more stable and outperforms traditional speckle nulling by 10% in suppression in the presence of white detector noise

Novel implementation of a Kalman filter for speckle nulling with a fiber injection unit

High dispersion coronagraphy (HDC) is a technique that combines high contrast imaging techniques with high spectral resolution spectroscopy to directly characterize exoplanets and provide key information such as chemical composition, temperature, and rotational velocity. A consequence of adaptive optics systems used in direct imaging is the formation of residual bright spots of star lights, called speckles, in the final image. Due to the large difference in brightness between host stars and their planets, these speckles can easily obscure potential exoplanets. In a previous demonstration, it was shown that using monochromatic light and a fiber injection unit (FIU), simulated exoplanet light can be directed to a high-resolution spectrograph. The method had speckle suppression that exceeding conventional image-based speckle nulling. With a previous Kalman filter estimator implementation, we found that with the implementation of the algorithm, speckle suppression was even more stable and outperformed traditional speckle nulling. In this update to the estimator, progress has been made in terms of a new filter design, and better estimates of the physical parameters in the laboratory, resulting in a higher speckle nulling performance

Commissioning and performance results of the WFIRST/PISCES integral field spectrograph

The Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) is a high contrast integral field spectrograph (IFS) whose design was driven by WFIRST coronagraph instrument requirements. We present commissioning and operational results using PISCES as a camera on the High Contrast Imaging Testbed at JPL. PISCES has demonstrated ability to achieve high contrast spectral retrieval with flight-like data reduction and analysis techniques.Comment: Author's copy - Proceedings of SPIE Volume 10400. Citation to SPIE proceedings volume will be added when availabl

Wavefront control for minimization of speckle coupling into a fiber injection unit based on the electric field conjugation algorithm

A fiber injection unit situated in the focal plane behind a coronagraph feeding a high resolution spectrograph can be used to couple light from an exoplanet to obtain high resolution spectra with improved sensitivity. However, the signal-to-noise ratio of the planet signal is limited by the coupling of starlight into the single mode fiber. To minimize this coupling, we need to apply a control loop on the stellar wavefront at the input of the fiber. We present here a wavefront control algorithm based on the formalism of the Electric Field Conjugation (EFC) controller that accounts for the effect of the fiber. The control output is the overlap integral of the electric field with the fundamental mode of a single mode fiber. This overlap integral is estimated by sending probes to a deformable mirror. We present results from simulations, and laboratory results obtained at the Caltech Exoplanet Technology Lab’s transmissive testbed. We show that our approach offers a significant improvement in starlight suppression through the fiber relative to a conventional EFC controller. This new approach improves the contrast of a high contrast instrument and could be used in future missions

Achromatizing scalar vortex coronagraphs with radial phase mask dimples

The Habitable Worlds Observatory mission will require coronagraphs capable of achieving contrasts of 1e-10 to detect exo-Earths. The choice of coronagraph depends on finding a solution that is achromatic within a 20\% bandwidth, insensitive to low order aberrations and polarization independent. We present two scalar vortex phase mask designs which employ a Roddier phase dimple and a dual zone phase dimple to improve the achromatic performance by addressing the chromatic stellar leakage not handled by the vortex. We show that using these dimples, it is possible to substantially improve the broadband contrast performance of existing scalar vortex phase masks.Comment: Conference Proceedings of SPIE: Techniques and Instrumentation for Detection of Exoplanets XI, vol. 12680 (2023