NIRWFS performance measurements presented in this page were obtained with the 188-element DM (AO188/NIRWFS)
prior to May 2024 and with the 3228-element DM in May 2024 (AO3k/NIRWFS).
The AO3k/NIRWFS May 2024 measurements were obtained in good seeing (0.4-0.6"). The AO188/NIRWFS measurements
probed median to poor seeing conditions, and also included off-axis performance degradation, field of view, and dithering accuracy.
AO3k/NIRWFS Image Quality - good seeing conditions
AO3k/NIRWFS image quality shown here for better than average seeing conditions
Conditions
Measurements were taken on the second half the night May 24 UT.
The seeing averaged 0.5" according to the Maunakea DIMM ,
and ranged from 0.35" to 0.7".
Some clouds were present, resuling in flux extinction (listed in unit of magnitude in some of the figures in this section).
CHARIS image quality - bright star
AO3k/NIRWFS observation of star Eps Boo (mH=0.13 before extinction) with CHARIS. Left: images and estimated Strehl ratios, Right: Radial profiles.
AO3k/NIRWFS observation of star Eps Boo (mH=0.13 before extinction) with CHARIS in coronagraph mode. Left: images, Right: Radial profiles.
CHARIS image quality vs. mH and wavelength
AO3k/NIRWFS observation of star BD192766 (mH=6.95) with CHARIS, with 1.91 mag of extinction (effective mH=8,86).
Left: images, Right: Radial profiles.
AO3k/NIRWFS performance vs. wavelength (left) and mH (right).
Right: Colors indicate wavelength, ranging from 1.15um (purple) to 2.3um (red)
AO3k/NIRWFS + SCExAO image quality
AO3k/NIRWFS is compatible with SCExAO. Both control loop can be running, provided the target is sufficiently bright in both NIR and visible light.
By combining the two xAO loops, the image quality and stability is enhanced.
On-sky AO3k/NIRWFS + SCExAO PSF without (left) and with (right) coronagraph.
AO3k/NIRWFS running at 1kHz, SCExAO visible pyramid WFS running at 2kHz
On-sky AO3k/NIRWFS + SCExAO PSF with VAMPIRES multi-band imaging under poor seeing (~1.3")
Palila camera image quality (Y band), with coronagraph & 25nm astrogrid
On-sky AO3k/NIRWFS + SCExAO PSF with Palila in Y band + coronagraph, under poor seeing (~1.3")
NIRWFS Strehl Ratio Measurements (measured with 188-element DM)
AO3k/NIRWFS image quality is significantly better than the AO188/NIRWFS results shown in this section, but has
not yet been extensively measured in median to poor seeing conditions. Observers should use this performance as lower limits under median to poor conditions
Conditions and Targets
The on-sky results presented below where taken during the engineering night of May 3, 2023. We
ran the AO loop at 500 Hz with the YJH50 dichroic beamsplitter (see the Technical description page for more details).
The seeing was above average: 0.7 to 1.1". We observed several targets with similar magnitudes
in J and H. Images were recorded with SCExAO's internal SWIR camera Palila (First Light Imaging
C-RED 2, y- to H-band), and the CHARIS integral field spectrograph in broadband mode (J- to
K-band).
H-band Strehl measurements obtained with SCExAO's Palila camera, over a few
seconds, for targets with various magnitudes. Each image is 2x2".
Strehl Ratio vs. H-band Magnitude
Compilation of all the Strehl measurements taken with SCExAO's Palila camera in
y-, J- and H-band. This includes times where we were tuning various parameters,
so some Strehl values can be much lower than optimal. The higher values for each
magnitude would represent the performance of the loop in normal conditions. The
Strehl ratio is over 40% until magnitude ~9, then decreases. This was done with
the YJH50 dichroic, so the result would be shifted by ~+0.75 magnitude with the
K-band dichroic, and ~-1.75 with the YJH90 dichroic.
Strehl Ratio vs. wavelength
Strehl ratio measurements in y-, J- and H-band with SCExAO's Palila camera, on
the target α Boo. A dark hole (control region of the deformable mirror) is
visible, even at short wavelengths. This is a sign that the correction is
excellent, even better than with the curvature wavefront sensor for which this
dark hole was never observed.
Strehl ratio measurements in J-, H- and K-band with CHARIS, on the target X Boo.
A dark hole (control region of the deformable mirror) is visible, even at short
wavelengths. This is a sign that the correction is excellent, even better than
with the curvature wavefront sensor for which this dark hole was never observed.
Strehl ratio measurements for the best frame of each target, for each wavelength
slice of CHARIS in broadand mode. Most curves tend to plateau and even decrease
after 2 μm, which is probably an effect of the increased thermal background
that was not subtracted properly. Otherwise, the Strehl ratio evolves pretty
linearly with wavelength.
Strehl ratio measurements on the target X Boo, for all the 30 s CHARIS frames
recorded on this target.
Strehl Ratio vs. separation
Strehl ratio measurements on the binary ξ Boo AB (H-mag ~5 for both stars).
The loop was closed on ξ Boo A, then the NIRWFS was steered on the companion
ξ Boo B. The seeing was about 0.8” with high altitude turbulence and
relatively high wind. The Strehl ratio of ξ Boo B is reduced by ~50% compared
to ξ Boo A, with a strong wind-driver halo visible. The effect of
anisoplanetism depends strongly on the atmospheric conditions.
Field of View (FoV)
Measured with AO188/NIRWFS.
There are two FoVs to consider: The FoV of the wavefront sensor in a fixed position, and the FoV
of the instrument as a whole, including the steering capability (the patrol FoV).
In both PyWFS and FPWFS, the required FoV is 2.8x2.8”, defined by the control region of the
ALPAO 64x64 DM. It is much smaller for the 188 DM. The FoV of the PyWFS was measured at 5x6”,
and the FoV of the FPWFS is 4x5”.
The patrol FoV was measured by moving the calibration source and recentering the image using the
steering mirror.
It is over ±10” vertically, >+7 and <-20” horizontally. The range is good, but it will be
centered better horizontally in the future.
PyWFS images for extreme off-axis targets, where a vignetting starts to
be noticed.
