Segmented telescopes are a possible approach to enable large-aperture space telescopes for the direct imaging and spectroscopy of habitable worlds. However, the increased complexity of their aperture geometry, due to the central obstruction, support structures and segment gaps, makes high-contrast imaging very challenging. The High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed was designed to study and develop solutions for such telescope pupils using wavefront control and coronagraphic starlight suppression. The testbed design has the flexibility to enable studies with increasing complexity for telescope aperture geometries starting with off-axis telescopes, then on-axis telescopes with central obstruction and support structures - e.g. the Wide Field Infrared Survey Telescope (WFIRST) - up to on-axis segmented telescopes, including various concepts for a Large UV, Optical, IR telescope (LUVOIR). In the past year, HiCAT has made significant hardware and software updates in order to accelerate the development of the project. In addition to completely overhauling the software that runs the testbed, we have completed several hardware upgrades, including the second and third deformable mirror, and the first custom Apodized Pupil Lyot Coronagraph (APLC) optimized for the HiCAT aperture, which is similar to one of the possible geometries considered for LUVOIR. The testbed also includes several external metrology features for rapid replacement of parts, and in particular the ability to test multiple apodizers readily, an active tip-tilt control system to compensate for local vibration and air turbulence in the enclosure. On the software and operations side, the software infrastructure enables 24/7 automated experiments that include routine calibration tasks and high-contrast experiments. In this communication we present an overview and status update of the project, both on the hardware and software side, and describe the results obtained with APLC wavefront control.
We design and fabricate arrays of diffractive optical elements (DOEs) to realize neutral atom micro-traps for
quantum computing. We initialize a single atom at each site of an array of optical tweezer traps for a customized
spatial configuration. Each optical trapping volume is tailored to ensure only one or zero trapped atoms.
Specifically designed DOEs can define an arbitrary optical trap array for initialization and improve collection
efficiency in readout by introducing high-numerical aperture, low-profile optical elements into the vacuum
We will discuss design and fabrication details of ultra-fast collection DOEs integrated monolithically and coaxially
with tailored DOEs that establish an optical array of micro-traps through far-field propagation. DOEs, as mode
converters, modify the lateral field at the front focal plane of an optical assembly and transform it to the desired field
pattern at the back focal plane of the optical assembly. We manipulate the light employing coherent or incoherent
addition with judicious placement of phase and amplitude at the lens plane. This is realized through a series of
patterning, etching, and depositing material on the lens substrate. The trap diameter, when this far-field propagation
approach is employed, goes as 2.44λF/#, where the F/# is the focal length divided by the diameter of the lens
aperture. The 8-level collection lens elements in this presentation are, to our knowledge, the fastest diffractive
elements realized; ranging from F/1 down to F/0.025.
For practical quantum computing, it will be necessary to detect the fluorescence from trapped ions using microscale ion
trap chips. We describe the first design, fabrication and assembly of a set of diffractive optics for intimate integration
into the trap chip and for coupling this fluorescence into multimode fibers. The design is complicated by the constraints
of the ion trap environment. In addition, the choice of available materials is restricted to those compatible with ultrahigh
vacuum. The completed optics-ion trap assembly has successfully demonstrated ion trapping, as well as ion shuttling,
with no necessary modifications to the trapping and shuttling voltage levels.
Phase retrieval is a promising method for optical system and surface metrology that makes use of intensity
measurements of diffraction patterns. An iterative algorithm is used to solve the inverse problem to find the phase of the
field producing the measured intensity distributions. For practical reasons, such as the reduction of coherent artifacts or
to improve the signal-to-noise ratio of the measured data, it is often desirable to measure intensity distributions using
broadband illumination. It is possible to perform phase retrieval with broadband data by incorporating a broadband
model of the system into the phase retrieval algorithm. To do this, the system is modeled at several discrete wavelengths
and the results from each are summed incoherently to produce a broadband result. This significantly increases the
computational load. We show here that when aberrations are small, accurate estimates of the OPD distribution, on the
level of &lgr;/1000 RMS error, can be achieved using data with bandwidth up to about 10% as the input to a phase retrieval
algorithm that assumes monochromatic data.
Phase retrieval can be useful in the measurement of optical surfaces and systems. It distinguishes itself through the simplicity of the experimental apparatus, just a detector array which collects light near a focal plane. Aspherics can be measured without null optics. The challenging part of the method is the estimation of the wavefront from the near-focus intensity measurements to reconstruct the wavefront.