Optimizing the subwavelength grating of L-band annular groove phase masks for high coronagraphic performance

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Volume 595 (November 2016)

A&A, 595 (2016) A127

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Table 1

Grating parameters, expected and measured broadband rejection ratios at L-band (3.5−4.0 μm) and M-band (4.4−5.0 μm) for our AGPMs after fabrication.

	w _t	h	α	Expected R	Measured R	Expected R	Measured R
Name	[μm]	[μm]	[degrees]	(L-band)	(L-band)	(M-band)	(M-band)

AGPM-L5	0.630 ± 0.015	4.90 ± 0.20	3.20 ± 0.20	30−2400	550	10−130	80
AGPM-L6^a	0.625 ± 0.015	4.57 ± 0.20	3.20 ± 0.20	20−1600	150	10−50	30
AGPM-L7^a	0.625 ± 0.015	4.82 ± 0.20	3.45 ± 0.20	20−1400	550	10−110	N/A
AGPM-L8	0.645 ± 0.015	4.86 ± 0.20	3.45 ± 0.20	30−270	50	10−80	N/A
AGPM-L9^b	0.750 ± 0.010	5.10 ± 0.05	2.45 ± 0.10	20−110	30	10−40	20
AGPM-L10^b	0.630 ± 0.010	5.20 ± 0.05	2.10 ± 0.10	10−40	20	70−450	90
AGPM-L11^b	0.650 ± 0.010	4.92 ± 0.05	2.22 ± 0.10	40−670	70	110−520	240
AGPM-L12^b	0.650 ± 0.010	4.92 ± 0.05	2.22 ± 0.10	40−670	70	110−520	120
AGPM-L13^b	0.590 ± 0.010	4.67 ± 0.05	2.45 ± 0.10	30−250	110	70−250	150
AGPM-L14^c	0.615 ± 0.010	4.67 ± 0.05	2.45 ± 0.10	70−1860	370	50−160	90
AGPM-L15	0.630 ± 0.010	4.67 ± 0.05	2.45 ± 0.10	130−2300	630	40−120	70

Notes.

^(a)

Installed in the Keck/NIRC2 camera.

^(b)

Chosen for grating tuning demonstration.

^(c)

Installed in the LBT/LMIRCam camera.

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