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# Enhanced high-dispersion coronagraphy with KPIC phase II: design, assembly
and status of sub-modules

N. Jovanovica B. Calvina M. Portera T. Schofielda J. Wanga M. Robertsa G.
Ruaneb J. K. Wallaceb R. Bartosb J. Pezzatoa J. Colborna J. R. Delormea,c D.
Echeverria D. Maweta,b C. Z. Bondd S. Cetrec S. Lilleyc S. Raglandc P.
Wizinowichc R. Jensen-Clemd a Department of Astronomy  California Institute of
Technology  1200 E. California Blvd  Pasadena  CA  91125  USA;
b Jet Propulsion Laboratory  California Institute of Technology  4800 Oak
Grove Drive  Pasadena  CA  91109  USA;
c W. M. Keck Observatory  65-1120 Mamalahoa Hwy  Kamuela  HI  96743  USA;
d Department of Astronomy & Astrophysics  University of California  Santa Cruz
CA 95064  USA;

###### Abstract

The Keck Planet Imager and Characterizer (KPIC) is a purpose-built instrument
for high-dispersion coronagraphy in the K and L bands on Keck. This instrument
will provide the first high resolution (R$>$30,000) spectra of known directly
imaged exoplanets and low-mass brown dwarf companions visible in the northern
hemisphere.

KPIC is developed in phases. Phase I is currently at Keck in the early
operations stage, and the phase II upgrade will deploy in late 2021. The goal
of phase II is to maximize the throughput for planet light and minimize the
stellar leakage, hence reducing the exposure time needed to acquire spectra
with a given signal-to-noise ratio. To achieve this, KPIC phase II exploits
several innovative technologies that have not been combined this way before.
These include a 1000-element deformable mirror for wavefront correction and
speckle control, a set of lossless beam shaping optics to maximize coupling
into the fiber, a pupil apodizer to suppress unwanted starlight, a pupil plane
vortex mask to enable the acquisition of spectra at and within the diffraction
limit, and an atmospheric dispersion compensator. These modules, when combined
with the active fiber injection unit present in phase I, will make for a
highly efficient exoplanet characterization platform.

In this paper, we will present the final design of the optics and opto-
mechanics and highlight some innovative solutions we implemented to facilitate
all the new capabilities. We will provide an overview of the assembly and
laboratory testing of the sub-modules and some of the results. Finally, we
will outline the deployment timeline.

###### keywords:

Wavefront sensing, high contrast imaging, exoplanets, high dispersion
coronography, high resolution spectroscopy

##  1 INTRODUCTION

The characterization of exoplanetary atmospheres demands innovative new
approaches which improve on sensitivity and precision. High dispersion
coronography (HDC) is one such approach that provides the ability to do
species-by-species molecular characterization (e.g. oxygen, water, carbon
dioxide, methane), thermal (vertical) atmospheric structure, planetary spin
measurements (length of day), and potentially Doppler imaging of atmospheric
(clouds) and/or surface features (continents versus oceans) [1]. HDC optimally
combines high contrast imaging techniques such as adaptive optics/wavefront
control plus coronagraphy to high resolution spectroscopy [1, 2]. One approach
that is being explored is to use an optical fiber to route the light of the
known planet from the focal plane to the spectrograph. A single-mode fiber
(SMF) is the ideal transport vehicle owing to the fact it has a field-of-view
(FOV) that can be matched to the 1 $\lambda/D$ width of the point spread
function (PSF), enabling efficient coupling for the planet light and
suppression of unwanted star light. In addition, its narrow FOV reduces the
amount of sky background injected into the spectrograph, which can be several
orders of magnitude greater in the case of a seeing-limited spectrograph.

Several projects have been initiated to realize this new technique from the
ground including: the Keck Planet Imager and Characterizer (KPIC) [3, 4],
which combines Keck AO and NIRSPEC, the Rigorous Exoplanetary Atmosphere
Characterization with High dispersion coronography instrument (REACH) [5],
which combines SCExAO and IRD and High-Resolution Imaging and Spectroscopy of
Exoplanets (HiRISE), which combines SPHERE and CRIRES+[6]. The phase I version
of KPIC and the REACH instrument are both transitioning from commissioning to
early science at the time of writing of this article and offer complimentary
wavelength coverage across the near-IR (NIR) on Maunakea (REACH operates from
y-H and KPIC operates in K and L bands), while HiRISE is still in the
development stage.

KPIC consists of a NIR pyramid WFS (PyWFS), which provides advanced wavefront
correction and a Fiber Injection Unit (FIU), which injects the light into
optical fibers, that are routed to NIRSPEC. KPIC is being developed in phases.
Phase I consisted of the PyWFS and a basic FIU, which were deployed to Keck in
the fall of 2018, have been commissioned and are now routinely used for
scientific observations. This new NIR WFS provides exceptional correction,
especially on redder targets too faint for the Shack-Hartmann [7]. Phase II
consists of a series of upgrades to the FIU, which aim to maximize the planet
light coupled to the fiber, while minimizing the amount of stellar leakage
(important for HDC) so as to minimize the integration time to reach a given
SNR [8]. Phase II is currently undergoing laboratory testing and will be
deployed in the fall of 2021 to replace the phase I FIU optical layout at
Keck. Here we provide an overview of the phase II design and present some of
the laboratory characterization for the various sub-modules.

##  2 Opto-mechanical design

Owing to the fact that KPIC is located in a small space inside Keck AO, KPICs
optics are mounted on a vertical plate. The plate is mounted on kinematics so
that the phase I plate at Keck could be replaced with the phase II plate in
late 2021. The opto-mechanical design of the phase II plate can be seen in
Fig. 1, which we will describe in detail.

---
Figure 1:  A CAD drawing of the phase II version of the fiber injection unit
for KPIC. (Left) View from the front. (Right) View from the rear. All major
opto-mechanical modules are labelled, along with the direction of propagation
of the beam through the system.

The converging beam on its way to NIRC2 is picked off and redirected to KPIC
via three gold mirrors (not shown in 1). The purpose of the KPIC plate is to
provide a relay for the light to the final focal plane, which has an optimized
F/# set to maximize coupling to the fiber bundle, while providing sufficient
focal/pupil planes for all the control and beam manipulation optics that
maximize planet light coupling while minimizing star light leakage. To this
end, the back bone of the KPIC design is a double optical relay that consists
of two off-axis parabolic (OAP) mirrors. The OAPs are oriented the incorrect
way with respect to the incoming beam. In this arrangement there are
significant aberrations in the collimated beam spaces, but this helps preserve
the field in the downstream focal planes. However, a single OAP relay used
like this would induce a large field tilt and therefore a second relay is
needed to flatten the field once again. A final OAP is then used (the correct
way around) to recollimate the beam one last time before it is focused using a
custom triplet lens (CaF2, ZnS, AMTIR-1, Rainbow Research Optics) onto the
fiber bundle.

This optical arrangement creates three pupil planes. In the first pupil plane,
a 1000 element deformable mirror (DM, Kilo-C-3.5, Boston Micromachines) can be
seen. It has a protective window to prevent advanced aging, which can occur
when operating the DM in a high humidity environment. The window is made from
CaF2 because it is transparent across the entire operating range of KPIC (y-L
bands). The DM will provide a significant increase in the number of actuators
compared to the native Keck AO DM, which has 349, increasing the control
radius and reducing the fitting error in the correction. In addition, the DM
will have lower latency electronics and can be driven at kHz rates also
helping to offer a better adaptive optics correction. It will be mounted on a
rail so that it can be easily removed/replaced when the plate needs to be
transported.

The PyWFS pickoff is a watermill style wheel located immediately after the DM.
The switching mechanism consists of a rotation stage (Conex-AG-PR100P,
Newport) that drives the watermill like optics holder. To avoid mechanical
collisions, the optics holder is offset from the rotator by a shaft and
bearing housing. The mechanism is used to select the light utilized for
wavefront control by the PyWFS. The reflected beam can be steered to adjust
the pointing into the PyWFS. Each optic in the wheel can be adjusted in pitch
by rotating the wheel and in yaw by a compact flexure-based adapter used to
hold the optic cells to the hub of the wheel. This is useful for co-aligning
the pointing of the various optics. However, to course align the entire
mechanism, the sub-module is fitted with push/pull actuators and springs that
enable the beam to be reflected accurately towards the PyWFS.

As the PyWFS is sensitive from y-K band, it could in principle be used across
this range, assuming the cold and warm filters in its beam path are upgraded
from that of the phase I design. The pickoff mechanism provides 4 slots for
optics. Three slots will be reserved for custom dichroics to share light with
the PyWFS. One will be for an AR coated piece of glass that matches the
physical dimensions of the other optics in the wheel. The purpose of this
optic is to offset any alignment beam (pupil shift) as if it were passing
through an actual beamsplitter, but allow for the alignment beam to be fully
transmitted, unlike the dichroics. This optic is critical to alignment and
maintenance of KPIC as identified in phase I.

In the second pupil plane, a corongraphic module with a vector vortex mask [9]
and a grey scale micro-dot apodizer (MDA) [10] is located. See Fig. 4 for
details. Both masks are used for suppressing starlight. The vortex mask is
used to enable the vortex fiber nulling (VFN) mode of operation, which
provides an inner working angle of $<1\lambda/D$ [11, 12, 13, 14]. Please see
Ref. 15 of this conference for the latest update on this mode. At such close
separations, KPIC could directly collect the spectra of many RV planets for
the first time. On the other hand, the MDA is designed to suppress starlight
in the focal plane from 2-10$\lambda/D$ at the expense of throughput. The
coronagraphic mechanism consists of two linear stages (Q-545.241, PI), which
allows the coronagraphic masks to be inserted into and aligned with the beam.
For alignment purposes, the tracking camera (outlined below) can be used in
pupil-viewing mode. Both masks operate without Lyot stops downstream.

Immediately after the coronagraphic masks is an atmospheric dispersion
corrector (ADC), which aims at correcting for the differential atmospheric
refraction and restoring the PSF, to a single spot, essential to boosting
coupling to the fibers. The module consists of 2 sets of 3 prisms (BaF2, CaF2,
ZnSe), which counter rotate with respect to the elevation axis of the
telescope. Two compact rotation stages (PR-50, Micronex) are used to allow the
prisms to rotate with respect to one another and track the elevation axis,
which rotates in the pupil in fixed field mode. Each stage uses a magnetic
encoder to keep track of its position. A lookup table of rotation angle
offsets with respect to the elevation axis for each prism as a function of
Zenith angle is used to drive the stages during observations. This table is
generated through detailed simulations of the properties of the atmosphere and
prisms. The prisms in the mechanism are optimized for operation across J to L
band. More details about the optical design and performance of the ADC can be
found in Ref. 16.

Figure 2 shows some CAD images of the ADC mechanism. The prisms are mounted in
custom machined cells. Their separation and parallelism is maintained with
precision shims, while their clocking is based on the prisms each having a
flat side (i.e. D-shaped) pressed against a reference flat in the cell. The
cell is secured to the stage with spring loaded fasteners which allow for
slight adjustments in the pitch and yaw so the input facet of each prism set
can be aligned perpendicular to the optical axis. Once this step is complete,
the rotators need to be secured to one another so the rotation axis of the two
motors is parallel. This can be achieved by using a flexure-based mounting
plate as shown in the figure. By adjusting the thickness of the washers for
the two threaded bolts used to keep the opposite end of the rotators together,
its possible to adjust the co-alignment of the two mechanisms. Once assembled,
the entire assembly will be located with a pin on the master plate. The far
end of the mechanism can be swiveled about this pin to adjust pitch and the
thickness of the spacers/washers under the far end can be used to adjust yaw.
In this way, all the degrees of freedom needed to align the ADC mechanism can
be provided in an extremely compact form factor.

---
Figure 2:  The ADC opto-mechanical assembly. (Right) A cross-sectional view
showing the prisms mounted in their cells, the cells mounted in the rotation
stages, and the stages mounted on the adapter plates. The angle of the prisms
with respect to the axis of rotation can be adjusted with the plungers. The
angle between the two stages can be adjusted with the flexure plate at the
bottom and the spacers at the top, and the angle of the entire assembly with
respect to the beam on the master plate can be adjusted using the pivot pin
and the flexure based adapter.

A tip/tilt mirror (S-330.8SL, PI) is located in the final pupil plane of the
system. The TTM is used to steer the beam in the focal plane to align it with
the core of the optical fibers in the bundle. It has two adjusters that allow
the reflected beam to be coarsely aligned in the right direction. The purpose
of the adjusters is to allow for the bulk TTM assembly to be steered to align
the beam with the tracking camera and back end optics without using precious
range on the TTM itself. To do this, the TTM will be set to the middle of its
range in X and Y and then be steered using the course alignment mechanisms. A
gold coated mirror, is attached to the TTM mechanism via a flexure-based
holder. The holder applies the lightest pre-load on the mirror laterally,
preventing deformations and hence unwanted aberrations.

The beam is next incident on a flat mirror, which directs it towards the
tracking camera pickoff (TCP) and ultimately the fiber injection. The TCP
consists of a linear translation stage (N-565.360, PI) that can switch between
three optics. One is used for alignment as was the case for the PyWFS pickoff.
The other two can be freely chosen to split the light between tracking and
science as needed. The TCP optics are mounted in a single mount, which can be
aligned in pitch and yaw. However, there is no way to adjust the differential
alignment between the beams reflected by the three optics. This is acceptable
because the optics are co-mounted so the differential pointing is very small
(a few $\lambda/D$) and the FOV of the tracking camera is relatively large
($\sim 165\times 132\lambda/D$).

The light reflected by the dichroics is directed to the tracking camera
(C-red2, FirstLight Imaging), which has several observing modes. These include
a focal plane viewing mode, used for tracking targets and NIR imaging, as well
as a pupil plane viewing mode and a Zernike WFS mode. The internal optics
inside the tracking camera module can be seen in Fig. 3. The focal plane
viewing mode provides a beam with an F/#=39, which results in a plate scale of
$\sim 8$ mas/pixel and hence almost 3 pixels/FWHM at the short end of J-band.
The focal plane viewing mode is used to track the star and guide on the fiber,
while the beam transmitted by the TCP dichroic goes directly to a focusing
optic that is used to inject the light into the fiber bundle. The tracking
camera images are used to drive the TTM in KPIC to steer the beam to the fiber
and maintain alignment. A corner cube is used to steer light reverse injected
from the bundles onto the tracking camera so that the position of the bundle
can be determined with respect to the beam from Keck AO.

---
Figure 3:  The tracking camera opto-mechanical assembly. (Left) Focal plane
viewing configuration. (Center) Pupil plane viewing configuration. (Right) The
camera is mounted on a plate, which is pinned to the optics block. The entire
block is pinned to the master plates for easy removal and replacement for
servicing.

A linear stage is used to replace the optics in the beam path and switch
between the focal and pupil plane imaging configurations. In the pupil plane
viewing mode, the light passes through a Wollaston prism, which generates two
images of the pupil with orthogonal linear states of polarization. This is
necessary for the Zernike WFS mode and to avoid having two different modes,
the classical pupil plane imaging mode shares these optics. Each pupil plane
image subtends $\sim 200$ pixels on the C-red2. Given the Keck pupil has seven
segments across the primary, this provides about $28$ pixels/segment, which is
grossly over sampled, but is convenient for fully understanding the Zernike
WFS as well as providing a precise reference image for aligning the
coronagraphic masks to. The Zernike WFS is based on a mask with a phase dimple
placed in the intermittent focal plane of the tracking camera shown in Fig. 3.
The phase dimple is simply a pit in a glass substrate that injects a $\pi$
phase shift for the light within the FWHM of the PSF with respect to the light
outside this. This helps convert phase aberrations into intensity modulations
the C-red2 can see. KPICs Zernike WFS is a vector mask, which means it does
this for both polarizations, which should provide a superior sensitivity. To
activate this mode, the TTM is used to steer the beam onto the phase dimple,
while classical pupil imaging is conducted by passing the beam through the
optic away from the dimple. The Zernike WFS is an experimental module that
could be used to help improve the co-phasing for the primary mirror of Keck,
which would be an important demonstration for TMT and the ELT as well.

To improve access for servicing the camera, the C-red2 is mounted on a plate,
which is pinned to the optics block. To allow much easier mask replacements in
future, the entire assembly is pinned to the master plates. It can be easily
removed so masks can be exchanged outside of Keck AO and replaced without
needing a complex realignment.

In the beam path to the tracking camera is a filter wheel. This has 8 slots
which includes filters such as a J, H, and 1550 nm bandpass filter that has a
25 nm bandwidth. There will also be an open slot, and a block so dark’s can be
taken.

The beam transmitted by the tracking camera pickoff is next incident on the
beam shaping, or PIAA optics [17]. These lenses reshape the pupil illumination
from a flat-top to a quasi-Gaussian, which improves coupling into the SMF
[18]. An aspheric lens pair is needed to achieve this, which is mounted into a
fixed tube. The tube is mounted on a translation stage (Q-545.241, PI) used to
move it in/out of the beam as well as a 5-axis manual stage, that can be used
to carefully align the tube initially with the beam. In this way, the PIAA is
deployable and retractable. The mechanism can be seen in Fig. 4. The PIAA
lenses in KPIC phase II are optimized for operation in the K and L bands, the
primary science bands for HDC with KPIC.

---
Figure 4:  Several opto-mechanical assemblies. (Left) Beam shaping optics
mechanism. (Center) Coronagraphic mask switching mechanism. (Right) Fiber
injection port switching mechanism.

The final module is the injection port switching mechanism, which can be seen
in Fig. 4. Lenses are used to focus the beams onto the bundles with the
optimum F/#. KPIC Phase II will provide 3 ports. The ports mechanically align
the optical axis of the lenses with the bundles. The bundles can only be
translated in focus with respect to the lenses to maximize coupling (i.e.
position them at the focus of the lenses). Manual actuators which push compact
linear stages are used to achieve this and once aligned are fixed. A large
translation stage (VT-80, PI) is used to switch the port that is inserted into
the beam. The entire assembly can be adjusted manually in X/Y, pitch/yaw, to
align the ports to the optical axis of the instrument. This gets close, but
the final alignment of pitch/yaw is done with the aid of the TTM in KPIC.

KPIC phase II will offer a retractable light source, which can be deployed at
the input focal plane. This source will allow us to inject calibration light
at the input to KPIC for daytime testing and calibration purposes. This means
KPIC can receive light and can undergo testing while others are using Keck AO,
increasing the amount of time KPIC can be used for laboratory testing. This
was an upgrade identified by operating the phase I plate.

As a final note, all opto-mechanical mechanisms were designed with the
following constraints in mind: precision, accuracy, translation range,
footprint, speed, heat dissipation of $<$10 W each, operational temperatures
down to 0C on average, larger controllers could be placed 10 m away in the
electronics room, control was compliant with a Linux, Centos07 OS, no visible
encoder lights that could interfere with the WFS’s in Keck AO and if possible
the mechanisms should be a COTS parts. This greatly limited the number of
possible options for each application. The final devices reported here met
these requirements.

##  3 Assembly and status

The status of the phase II sub-modules at the time of writing of this article
is summarized in Fig. 5. Each sub-module as well as the master plates
everything is bolted to have a separate row in the table. The development
process flows through design, procurement/fabrication, assembly, testing and
integration and control software.

---
Figure 5:  Status of the development of the phase II sub-modules. Green means
complete, red incomplete, yellow partially completed and blue not applicable.
ZWFS refers to the Zernike WFS. I&T refers to integration and testing. Test
bench refers to custom optical bench where all modules are tested in isolation
initially. Plates means that the module has been integrated onto the master
plate as it will be at Keck and is undergoing testing at the system level.
Make it move refers to initial attempts to communicate with opto-mech. by any
means possible.

It is clear to see from the figure that most sub-modules have completed
optical design, mechanical design, procurement, fit testing and the final
assemblies have been built. In addition, control software has advanced beyond
the readiness of the mechanics and all mechanisms have been made to move, and
have low level libraries and higher level scripts to control sequenced motions
that can operate in Linux Centos07, the OS of choice for Keck computer
systems. Having access to control software at such an advanced stage is
beneficial to efficient I&T.

Once assembled, the sub-modules will undergo testing in two stages. Stage 1)
involves integrating the devices into a custom optical setup so they can be
tested in isolation initially, referred to as “Test bench” in the figure. Once
the basic parameters of the module have been tested in this setup, it will be
moved to the final assembly and integrated in the plates. This will allow
system level testing needed to fully qualify the module before deployment.
Once fully assembled, control scripts that aid acquisition, as well as various
forms of wavefront control will be produced and tested in the laboratory.

Images of some of the fully assembled modules are shown in Fig. 6. It can be
seen that the modules that have been tested on the test bench include the beam
shaping optics, the coronagraphs, the PyWFS pickoff and TCP. These were
accelerated because they posed a higher level of risk and needed to be
qualified early on to prevent delays down the track. The ADC is the only other
high risk element that has not been assembled or tested yet, owing to the
difficulty in locking down vendors to produce and AR coat the prisms. The
optics are about to be delivered and assembly and testing will begin in the
near future.

---
Figure 6:  Images of assembled sub-modules. (Top) The test bench used to test
each sub-module in isolation. The beam shaping (PIAA) sub-module is shown in
the center of the bench undergoing testing. The bench consists of a beam from
an optical fiber which is collimated and then passed through a mask that
replicates the Keck pupil, passes the beam through the optic under test before
either directing it towards a NIR camera used to image the beam (orange path),
or towards coupling optics used to inject the light into a SMF (green path).
These can be switched by removing/replacing a mirror on a magnetic mount.
(Lower left) The coronagraphic mechanism and the masks mounted in their
holder. (Center) The tracking camera optics block. (Right) The injection port
switching mechanism with one optic mounted.

The timeline for the remainder of the development is to have all modules fully
assembled and tested in the test bench by March 2021. They will then be
integrated into the plates and system level testing will begin. The project
will have a pre-ship review in late September 2021 and if successful, the
phase II plate will be deployed to the Keck II telescope in November.

##  4 Preliminary laboratory characterization

As seen in Fig. 5, four sub-modules have been characterized in the laboratory,
including the beam shaping optics, the coronagraphs, the PyWFS pickoff and the
TCP. The optical performance, including the shape of the PSF, the throughput
of the optic and the coupling to a SMF for the coronagraphs and PIAA optics is
presented in 19 and will not be repeated here. Here we instead report on some
of the key results for the other two mechanisms instead.

###  4.1 The PyWFS pickoff mechanism

The PyWFS pickoff is used to select the dichroic that will split the light
between the PyWFS and the FIU. A critical property of the mechanism is how
accurately the beam reflected towards the PyWFS could be aligned to the
optical axis, and its stability. To test this, mirrors were placed in each of
the four optic cells. A collimated laser beam was reflected from one of the
mirrors and imaged onto a detector. The centroid of the beam was noted and the
wheel rotated to the next mirror. At this position, the beam was co-aligned
with the position of the first by using the wheel and the flexure mechanism
mentioned above. This process was repeated for all four mirrors. This
demonstrated that there was sufficient range in the flexure mechanism to be
able to accurately co-align all four beams, arresting that concern.

Next, a script was executed that rotated the wheel from position 1 to 2, 2, to
3, 3 to 4, 4 to 3, 3 to 2, 2 to 1 on repeat to see how the centroids would
behave. The results are shown in the left panel of Fig. 7. It can be seen that
for each mirror, there are two unique clusters of centroids depending on
whether you approach that mirror from the left or the right (i.e. 1 to 2, or 3
to 2). After much testing it was determined that there was some hysteresis-
like effect and that if one were to approach mirrors 3 and 4 directly from the
home position, and mirrors 1 and 2 from the maximum angle of the stage (340∘),
then the scatter could be minimized as is shown in the right panel of Fig. 7.
This shows a significant reduction in the spread of the spots, which results
in a much more deterministic and reproducible alignment of the PyWFS beam as
one switches between optics. For reference the blue dashed circle shows the
requirement for the maximum misalignment with respect to the optical axis
allowed and the figure clearly shows that even without hysteresis
compensation, the mechanism meets specification.

---
Figure 7:  Scatter plot of the position of the centroid each time a mirror is
inserted into the beam with the PyWFS pickoff mechanism. (Left) Without and
(Right) With compensating for the hysteresis effect.

###  4.2 The tracking camera pickoff mechanism

The TCP will be used to split the light between the tracking camera and the
fiber injection ports. Although the tracking camera has a large FOV
(5.5$\times$4 arcsec), its important to make sure that the centroids from the
three co-mounted optics are aligned to within the FOV of the camera and their
pointings are highly repeatable. In a similar fashion to the PyWFS pickoff
tests, a laser beam was bounced off a mirror in the TCP and an image formed.
The centroid was recorded, the TCP mechanism switched to another mirror
position and the centroid recorded again. This process was repeated 240 times
over a period of 33 hrs. The results are shown in Fig. 8. It can be seen that
each mirror points in a unique direction, but that the spread in pointing
after successive moves away from and back to a given mirror is very small (see
right panel). This highlights that the pointing is highly repeatable. The
three mirrors have an offset in their pointing of the order of $\sim
5\lambda/D$, or 40 mas or 5 pixels on the C-red2. Given the size of the array
(640$\times$512), this is a minor offset and well within the central region of
the camera. As such, the mechanism can successfully co-point the three beams
and provides highly reproducible pointing to warrant application in KPIC phase
II.

---
Figure 8:  Scatter plot of the position of the centroid each time a mirror is
inserted into the beam with the TCP mechanism. (Left) Centroids and (Right)
RMS spread of centroids for each mirror.

##  5 Summary

The KPIC instrument is already offering enhanced exoplanet characterization
capabilities at Keck. Phase II will provide a series of sub-module upgrades
that will improve planet throughput and reduce stellar leakage, ultimately
reducing overall integration times. In this paper we have provided a detailed
overview of the entire opto-mechanical design and its rationale. The phase II
modules are partly built and testing is on-going in the laboratory. The goal
is to complete all sub-modules in early 2021, and move to integrating them
into the system. This will provide a 6 month window to verify, validate and
develop control scripts so the upgrade can be deployed in late 2021.

###### Acknowledgements.

This work was supported by the Heising-Simons Foundation through grants
#2019-1312 and #2015-129. G. Ruane was supported by an NSF Astronomy and
Astrophysics Postdoctoral Fellowship under award AST-1602444. We thank Dr.
Rebecca Jensen-Clem for loaning AOSE for use within the KPIC phase II testing.
Part of this work was carried out at the Jet Propulsion Laboratory, California
Institute of Technology, under contract with the National Aeronautics and
Space Administration (NASA). W. M. Keck Observatory is operated as a
scientific partnership among the California Institute of Technology, the
University of California, and the National Aeronautics and Space
Administration (NASA). The Observatory was made possible by the generous
financial support of the W. M. Keck Foundation.The authors wish to recognize
and acknowledge the very significant cultural role and reverence that the
summit of Maunakea has always had within the indigenous Hawaiian community. We
are most fortunate to have the opportunity to conduct observations from this
mountain.

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