Ralf K. Heilmann,1,*
Jeffery Kolodziejczak,2
Alexander R. Bruccoleri,3
Jessica A. Gaskin,2
and Mark L. Schattenburg1
1Space Nanotechnology Laboratory, MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2NASA Marshall Space Flight Center, Huntsville, Alabama 35812, USA
3Izentis, LLC, Cambridge, Massachusetts 02139, USA
Ralf K. Heilmann, Jeffery Kolodziejczak, Alexander R. Bruccoleri, Jessica A. Gaskin, and Mark L. Schattenburg, "Demonstration of resolving power λ/Δλ > 10,000 for a space-based x-ray transmission grating spectrometer," Appl. Opt. 58, 1223-1238 (2019)
We present measurements of the resolving power of a soft x-ray spectrometer consisting of 200 nm period lightweight, alignment-insensitive critical-angle transmission (CAT) gratings and a lightweight slumped-glass Wolter-I focusing mirror pair. We measure and model contributions from source, mirrors, detector pixel size, and grating period variation to the natural linewidth spectrum of the Al- doublet. Measuring up to the 18th diffraction order, we consistently obtain small broadening due to gratings corresponding to a minimum effective grating resolving power with 90% confidence. Upper limits are often compatible with . Independent fitting of different diffraction orders, as well as ensemble fitting of multiple orders at multiple wavelengths, gives compatible results. Our data leads to uncertainties for the Al- doublet linewidth and line separation parameters two to three times smaller than values found in the literature. Data from three different gratings are mutually compatible. This demonstrates that CAT gratings perform in excess of the requirements for the Arcus Explorer mission and are suitable for next-generation space-based x-ray spectrometer designs with resolving power five to 10 times higher than the transmission grating spectrometer onboard the Chandra X-ray Observatory.
Ralf K. Heilmann, Minseung Ahn, Alex Bruccoleri, Chih-Hao Chang, Eric M. Gullikson, Pran Mukherjee, and Mark L. Schattenburg Appl. Opt. 50(10) 1364-1373 (2011)
Benjamin D. Donovan, Randall L. McEntaffer, James H. Tutt, Casey T. DeRoo, Ryan Allured, Jessica A. Gaskin, and Jeffery J. Kolodziejczak Appl. Opt. 57(3) 454-464 (2018)
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FWHM, half-power width, and fractional flux are listed for the central five CDBs. The results from each of the and CDBs are averaged, and differences are included in the errors. The half-power width along the cross-dispersion direction is , and 84% of flux is within the central five CDBs.
Line wavelengths, , (nm) and widths, , (eV) from various references.
Table 3.
Nominal As-Modeled X-ray Linewidths and Separationsa
Model Constants
Nominal Values
Description
236 fm, 0.42 eV
, Lorentzian FWHM
232 fm (0.413 eV)
, separation
[7,43] We assume the equivalencies listed in the first column. The wavelength unit, fm, is femto-meters (). For comparison, 1 pixel at orders extends over fm in wavelength space.
The list forms the set of parameters for Eq. (6). Fixed parameter values are listed in Column 2 for the fit cases defined in the table referenced in the top row.
Table 5.
18th Order Summary of Fits with Fixed Line Wavelengths and Widthsa
Fit ID
CDB
ROI pixels
pixels
(90% l.l.) from
(90% l.l.) from fit
DOF
(a)
0
143
15600
-
125.0
135
0.28
(b)
143
24500
-
133.6
135
0.48
(c)
143
21500
-
126.0
135
0.30
(d)
0
27
9100
8700
20.55
19
0.64
(e)
27
12600
12200
16.76
19
0.39
(f)
27
12100
12200
17.62
19
0.45
Rows (a)–(c) had a wide ROI; (d)–(f) had a narrow ROI. Effective resolving power values, , use dispersion distances . (90% l.l.) means 90% probability that is greater than the given value.
(, , ) are errors for (, , ). Effective resolving power values, , use dispersion distance for (a), (b), (h), and (i), for (c) and (d), for (e) and (f), and for (g). Best fit model comparisons with data are not shown for all cases because of similarity with other fits. Best fit models are compared with data in Fig. 17 for (a), (b), and Fig. 19 for (i). analysis was not performed on cases (c)–(g). Probability contours are displayed for (b) in Fig. 18 and (i) in Fig. 20.
Table 7.
Summary of Best Fit and Lower Limit Effective Resolving Power Results from the Most Sensitive Fit Casesa
FWHM, half-power width, and fractional flux are listed for the central five CDBs. The results from each of the and CDBs are averaged, and differences are included in the errors. The half-power width along the cross-dispersion direction is , and 84% of flux is within the central five CDBs.
Line wavelengths, , (nm) and widths, , (eV) from various references.
Table 3.
Nominal As-Modeled X-ray Linewidths and Separationsa
Model Constants
Nominal Values
Description
236 fm, 0.42 eV
, Lorentzian FWHM
232 fm (0.413 eV)
, separation
[7,43] We assume the equivalencies listed in the first column. The wavelength unit, fm, is femto-meters (). For comparison, 1 pixel at orders extends over fm in wavelength space.
The list forms the set of parameters for Eq. (6). Fixed parameter values are listed in Column 2 for the fit cases defined in the table referenced in the top row.
Table 5.
18th Order Summary of Fits with Fixed Line Wavelengths and Widthsa
Fit ID
CDB
ROI pixels
pixels
(90% l.l.) from
(90% l.l.) from fit
DOF
(a)
0
143
15600
-
125.0
135
0.28
(b)
143
24500
-
133.6
135
0.48
(c)
143
21500
-
126.0
135
0.30
(d)
0
27
9100
8700
20.55
19
0.64
(e)
27
12600
12200
16.76
19
0.39
(f)
27
12100
12200
17.62
19
0.45
Rows (a)–(c) had a wide ROI; (d)–(f) had a narrow ROI. Effective resolving power values, , use dispersion distances . (90% l.l.) means 90% probability that is greater than the given value.
(, , ) are errors for (, , ). Effective resolving power values, , use dispersion distance for (a), (b), (h), and (i), for (c) and (d), for (e) and (f), and for (g). Best fit model comparisons with data are not shown for all cases because of similarity with other fits. Best fit models are compared with data in Fig. 17 for (a), (b), and Fig. 19 for (i). analysis was not performed on cases (c)–(g). Probability contours are displayed for (b) in Fig. 18 and (i) in Fig. 20.
Table 7.
Summary of Best Fit and Lower Limit Effective Resolving Power Results from the Most Sensitive Fit Casesa