NIRWFS
System
Performance
Observing

AO3k-NIRWFS

Information for S26A observers

AO3k with NIRWFS is available to all observers in S26A.

Since the upgrade of the deformable mirror inside AO188, three modes are available to observers: AO188/NGS, AO188/LGS and AO3k/NIRWFS. When using visible wavefront sensing (AO188/NGS and AO188/LGS), the wavefront correction is limited to the 188 modes sensed by the WFS, so the performance is unchanged from the previous (pre-S25A) AO system. When using the NIRWFS (AO3k/NIRWFS mode), the near-IR pyramid wavefront sensor can control all illuminated actuators, providing high performance AO correction.
AO observers may choose AO3k/NIRWFS instead of AO188/NGS for improved image quality. For visible and NIR science observations, please check the throughput of the various pickoff mirrors that can be use, as some of the NIR light will be used for wavefront sensing.

The NIRWFS is a PI-type module. Service observations are not offered with the NIRWFS. According to Subaru Telescope's rules for PI-type instruments, please contact and include the PI, Julien Lozi (lozi_at_naoj.org), if you plan on submitting a proposal. If your proposal targets the galactic center, please also contact and include co-I Shogo Nishiyama (shogo-n_at_staff.miyakyo-u.ac.jp)

Before preparing the proposal, please read Planning Observations very carefully .

Introduction

The Near Infrared Wavefront Sensor (NIRWFS) is a wavefront sensor for the AO188/AO3k adaptive optics system of the Subaru Telescope. It uses most of the AO188 optics, and replaces the visible curvature wavefront sensor (CWFS) to control the 3228-element magnetic deformable mirror to perform the wavefront correction. It has three modes: a Pyramid WFS mode (PyWFS), a Focal Plane WFS mode (FPWFS) and a pupil imaging mode (See Technical description for more information about the design). Only the PyWFS mode is currently offered for Open-Use observations.

The open-use instruments that can currently benefit from the NIRWFS are IRCS. SCExAO, SCExAO+CHARIS, SCExAO+VAMPIRES, and SCExAO+REACH.

The NIRWFS only operates in NGS mode. It requires a bright star within 14 arcsec from the science target. A target brighter than H-mag = 9 to 13 is required to obtain a reasonable correction, depending on the spectrum of the star, and the dichroic beamsplitter pickoff selected. The upgraded system now allows to swap dichroic pickoffs during the night. See Planning Observations for more information.

Strehl ratios above 80% in H-band were demonstrated under good seeing conditions. (See Performance for more details).

AO3k/NIRWFS observation of star Eps Boo with CHARIS. Left: images and estimated Strehl ratios, Right: Radial profiles.

Modes supported since S25A:

SCExAO

The NIRWFS can be used with the following SCExAO modes :

CHARIS low-red broadband
CHARIS hi-res J, H or K-band
VAMPIRES imaging
REACH (Single mode fiber injection inside SCExAO feeding IRD)
CHARIS PDI
VAMPIRES PDI
Fast PDI

TIn S26A: The impact of the polarization of the NBS will be characterized in S25B, so PDI modes are available in shared risk mode.

Please consult the SCExAO instrument team prior to submitting observing proposals if using the NIRWFS.

IRCS

The IRCS observation modes that can use NIRWFS are below:

20 mas imaging (Y- to K-band)
Grism spectroscopy (zJ- to K-band)
Echelle mode (zJ- to K-band)
20 mas imaging polarimetry (Y- to K-band)
Grism spectropolarimetry (NIR settings)

L- and M- band observations, 52 mas imaging, and grism spectroscopy are NOT available due to the limitation of NIRWFS (vignetting, accuracy of the steering mirror movement, throughput of the dichroic, etc.). See IRCS observation with NIRWFS for details.

Dichroics availability for each mode

Dichroics	SCExAO/ CHARIS				SCExAO/ VAMPIRES	SCExAO/ REACH	IRCS
	lo-res	hi-res			imaging	spectro	imaging				echelle spectro
	J+H+K	J	H	K	I	Y+J+H	Y	J	H	K	zJ	J	H	K
K-band	Yes*	No	No	Yes	No	No	No	No	No	Yes	No	No	No	Yes
YJH50	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
YJH90	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Vis-HK	Yes†	No	No	Yes	Yes	Yes‡	No	No	Yes	Yes	No	No	Yes	Yes

* No J and H-band. † No J-band. ‡ No Y- and J-band.

Basic parameters

Location	Nasmyth focus (IR)
Spectral coverage of science path	0.6-2.4 um
Number of control elements	3228 (device), ~2700 (illuminated), ~2000 modes controlled
Deformable mirror	Magnetic actuation, model ALPAO3228
High-order WFS	NIR Pyramid Wavefront sensor with HgCdTe detector.
Control bandwidth	> 100 Hz, 500 to 2000 corrections/sec
NGS magnitude	-3 < H < 9-13 (Depending on the selected dichroic)
Off-axis steering	20 arcsec diameter
Wavelength range	0.95-1.8 um (y, J and H-band)

Technical Description

Performance

Planning Observations

Instrument citation

Please cite the following papers when you refer to the NIRWFS in your publication.

"AO3000 at Subaru: Combining for the first time a NIRWFS using First Light's C-RED ONE and ALPAO's 64x64 DM" Lozi et al. 2022, Proc. SPIE, vol. 12185, id. 1218533

"AO3k at Subaru: First on-sky results of the facility extreme-AO"

Contacts

Questions regarding this page should be directed to the primary support astronomer (Julien Lozi, lozi_at_naoj.org).

Please note that all numbers on these pages are subject to change as the performance of the NIR WFS is better determined.