Abstract

Coronagraphs for detection and characterization of exosolar earthlike planets require accurate masks with broadband performance in the visible and near infrared spectrum. Design and fabrication of image plane masks capable of suppressing broadband starlight to 1010 level contrast presents technical challenges. We discuss basic approaches, material choices, designs, and fabrication options for image plane masks with particular focus on material properties to obtain adequate spectral performance. Based on theoretical analysis, we show that metals such as Pt and Ni, and alloys such as Inconel, may be employed as promising mask materials that can meet broadband performance requirements.

© 2008 Optical Society of America

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References

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  1. JPL web site on Planet Quest: http://planetquest.jpl.nasa.gov/TPF/tpflowbarindex.cfm.
  2. M. J. Kuchner and W. A. Traub, "A coronagraph with a band-limited mask for finding terrestrial planets," Astrophys. J. 570, 900-908 (2002).
    [CrossRef]
  3. K. Balasubramanian, E. Sidick, D. W. Wilson, D. J. Hoppe, S. B. Shaklan, and J. T. Trauger, "Band-limited masks for TPF coronagraph," C.R. Phys. 8, 288-297, doi:10.1016/j.crhy.2007.03.001 (2002).
    [CrossRef]
  4. K. Balasubramanian, D. J. Hoppe, P. G. Halverson, D. W. Wilson, P. M. Echternach, F. Shi, A. E. Lowman, A. F. Niessner, J. T. Trauger, and S. B. Shaklan, "Occulting focal plane masks for terrestrial planet finder coronagraph--design, fabrication, simulations and test results," in Proceedings of IAU Colloquium 200, Direct Imaging of ExoPlanets (Cambridge U. Press, 2006), pp. 405-409.
  5. M. J. Kuchner and D. N. Spergel, "Notch filter masks: practical image masks for planet-finding coronagraphs," Astrophys. J. 594, 617-626 (2003).
    [CrossRef]
  6. J. T. Trauger, C. Burrows, B. Gordon, J. Green, A. Lowman, D. Moody, A. Niessner, F. Shi, and D. Wilson, "Coronagraph contrast demonstrations with the high contrast imaging testbed," Proc. SPIE 5487, 1330-1336 (2004).
    [CrossRef]
  7. Canyon Materials, Inc., San Diego, Calif., USA, http://canyonmaterials.com.
  8. J. T. Trauger and W. A. Traub, "A laboratory demonstration of the capability to image an Earth-like extrasolar planet," Nature 446, 771-773 (2007).
    [CrossRef] [PubMed]
  9. D. W. Wilson, P. D. Maker, J. T. Trauger, and T. B. Hull, "Eclipse apodization: realization of occulting spots and Lyot masks," Proc. SPIE 4860, 361-370 (2003).
    [CrossRef]
  10. V. Lucarini, J. J. Saarinen, K. E. Peiponen, and E. M. Vartiainen, Kramers-Kronig Relations in Optical Materials Research (Springer-Verlag, 2005).
  11. P. G. Halverson, M. Z. Ftaclas, K. Balasubramanian, D. J. Hoppe, and D. W. Wilson, "Measurement of wavefront phase delay and optical density in apodized coronagraphic mask materials," Proc. SPIE 5905, 59051I (2005).
    [CrossRef]
  12. E. Sidick and D. W. Wilson, "Behavior of imperfect band-limited coronagraphic masks in high contrast imaging system," Appl. Opt. 46, 1397-1407 (2007).
    [CrossRef] [PubMed]
  13. E. Sidick, "Requirements on optical density and phase dispersion of imperfect band-limited occulting masks in a broadband coronagraph," Appl. Opt. 46, 7485-7493 (2007).
    [CrossRef] [PubMed]
  14. A thin film design software from Thin Film Center, Inc., Tucson, Ariz., USA.
  15. G. Hass and L. Hadley, Optical Properties of Metals (AIP Handbook, 1972), pp. 6-124.
  16. www.specialmetals.com; also, www.espi.com.
  17. W. V. Goodell, J. K. Coulter, and P. B. Johnson, "Optical constants of Inconel alloy films," J. Opt. Soc. Am. 63, 185-188 (1973).
    [CrossRef]
  18. E. Sidick and K. Balasubramanian, "Effects of optical-density and phase dispersion of an imperfect band-limited occulting mask on the broadband performance of a TPF coronagraph," Proc. SPIE 6693, 66931C (2007).
    [CrossRef]
  19. A. Schüler, V. Thommen, P. Reimann, P. Oellhafen, G. Francz, T. Zehnder, M. Düggelin, D. Mathys, and R. Guggenheim, "Structural and optical properties of titanium aluminum nitride films (Ti1−xAlxN)," J. Vac. Sci. Technol. A 19, 922-929 (2001).
    [CrossRef]
  20. S. M. Aouadi, T. Maeruf, M. Sodergren, D. M. Mihut, S. L. Rohde, J. Xu, and S. R. Mishra, "Growth and characterization of nano-crystalline ZrN-Inconel structures," J. Vac. Sci. Technol. A 23, 998-1005 (2005).
    [CrossRef]
  21. W. Daschner, P. Long, M. Larsson, and S. H. Lee, "Fabrication of diffractive optical elements using a single optical exposure with a gray level mask," J. Vac. Sci. Technol. B 13, 2729-2731 (1995).
    [CrossRef]
  22. K. Balasubramanian, D. W. Wilson, R. E. Muller, B. D. Kern, and E. Sidick, "Thickness dependent optical properties of metals and alloys applicable to TPF coronagraph image masks," Proc. SPIE 6693, 66930Z (2007).
    [CrossRef]
  23. D. C. Moody and J. T. Trauger, "Hybrid Lyot coronagraph masks and wavefront control for improved spectral bandwidth and throughput," Proc. SPIE 6693, 66931I (2007).
    [CrossRef]

2007 (6)

J. T. Trauger and W. A. Traub, "A laboratory demonstration of the capability to image an Earth-like extrasolar planet," Nature 446, 771-773 (2007).
[CrossRef] [PubMed]

E. Sidick and D. W. Wilson, "Behavior of imperfect band-limited coronagraphic masks in high contrast imaging system," Appl. Opt. 46, 1397-1407 (2007).
[CrossRef] [PubMed]

E. Sidick, "Requirements on optical density and phase dispersion of imperfect band-limited occulting masks in a broadband coronagraph," Appl. Opt. 46, 7485-7493 (2007).
[CrossRef] [PubMed]

E. Sidick and K. Balasubramanian, "Effects of optical-density and phase dispersion of an imperfect band-limited occulting mask on the broadband performance of a TPF coronagraph," Proc. SPIE 6693, 66931C (2007).
[CrossRef]

K. Balasubramanian, D. W. Wilson, R. E. Muller, B. D. Kern, and E. Sidick, "Thickness dependent optical properties of metals and alloys applicable to TPF coronagraph image masks," Proc. SPIE 6693, 66930Z (2007).
[CrossRef]

D. C. Moody and J. T. Trauger, "Hybrid Lyot coronagraph masks and wavefront control for improved spectral bandwidth and throughput," Proc. SPIE 6693, 66931I (2007).
[CrossRef]

2005 (2)

P. G. Halverson, M. Z. Ftaclas, K. Balasubramanian, D. J. Hoppe, and D. W. Wilson, "Measurement of wavefront phase delay and optical density in apodized coronagraphic mask materials," Proc. SPIE 5905, 59051I (2005).
[CrossRef]

S. M. Aouadi, T. Maeruf, M. Sodergren, D. M. Mihut, S. L. Rohde, J. Xu, and S. R. Mishra, "Growth and characterization of nano-crystalline ZrN-Inconel structures," J. Vac. Sci. Technol. A 23, 998-1005 (2005).
[CrossRef]

2004 (1)

J. T. Trauger, C. Burrows, B. Gordon, J. Green, A. Lowman, D. Moody, A. Niessner, F. Shi, and D. Wilson, "Coronagraph contrast demonstrations with the high contrast imaging testbed," Proc. SPIE 5487, 1330-1336 (2004).
[CrossRef]

2003 (2)

M. J. Kuchner and D. N. Spergel, "Notch filter masks: practical image masks for planet-finding coronagraphs," Astrophys. J. 594, 617-626 (2003).
[CrossRef]

D. W. Wilson, P. D. Maker, J. T. Trauger, and T. B. Hull, "Eclipse apodization: realization of occulting spots and Lyot masks," Proc. SPIE 4860, 361-370 (2003).
[CrossRef]

2002 (2)

M. J. Kuchner and W. A. Traub, "A coronagraph with a band-limited mask for finding terrestrial planets," Astrophys. J. 570, 900-908 (2002).
[CrossRef]

K. Balasubramanian, E. Sidick, D. W. Wilson, D. J. Hoppe, S. B. Shaklan, and J. T. Trauger, "Band-limited masks for TPF coronagraph," C.R. Phys. 8, 288-297, doi:10.1016/j.crhy.2007.03.001 (2002).
[CrossRef]

2001 (1)

A. Schüler, V. Thommen, P. Reimann, P. Oellhafen, G. Francz, T. Zehnder, M. Düggelin, D. Mathys, and R. Guggenheim, "Structural and optical properties of titanium aluminum nitride films (Ti1−xAlxN)," J. Vac. Sci. Technol. A 19, 922-929 (2001).
[CrossRef]

1995 (1)

W. Daschner, P. Long, M. Larsson, and S. H. Lee, "Fabrication of diffractive optical elements using a single optical exposure with a gray level mask," J. Vac. Sci. Technol. B 13, 2729-2731 (1995).
[CrossRef]

1973 (1)

Appl. Opt. (2)

Astrophys. J. (2)

M. J. Kuchner and W. A. Traub, "A coronagraph with a band-limited mask for finding terrestrial planets," Astrophys. J. 570, 900-908 (2002).
[CrossRef]

M. J. Kuchner and D. N. Spergel, "Notch filter masks: practical image masks for planet-finding coronagraphs," Astrophys. J. 594, 617-626 (2003).
[CrossRef]

C.R. Phys. (1)

K. Balasubramanian, E. Sidick, D. W. Wilson, D. J. Hoppe, S. B. Shaklan, and J. T. Trauger, "Band-limited masks for TPF coronagraph," C.R. Phys. 8, 288-297, doi:10.1016/j.crhy.2007.03.001 (2002).
[CrossRef]

J. Opt. Soc. Am. (1)

J. Vac. Sci. Technol. A (2)

A. Schüler, V. Thommen, P. Reimann, P. Oellhafen, G. Francz, T. Zehnder, M. Düggelin, D. Mathys, and R. Guggenheim, "Structural and optical properties of titanium aluminum nitride films (Ti1−xAlxN)," J. Vac. Sci. Technol. A 19, 922-929 (2001).
[CrossRef]

S. M. Aouadi, T. Maeruf, M. Sodergren, D. M. Mihut, S. L. Rohde, J. Xu, and S. R. Mishra, "Growth and characterization of nano-crystalline ZrN-Inconel structures," J. Vac. Sci. Technol. A 23, 998-1005 (2005).
[CrossRef]

J. Vac. Sci. Technol. B (1)

W. Daschner, P. Long, M. Larsson, and S. H. Lee, "Fabrication of diffractive optical elements using a single optical exposure with a gray level mask," J. Vac. Sci. Technol. B 13, 2729-2731 (1995).
[CrossRef]

Nature (1)

J. T. Trauger and W. A. Traub, "A laboratory demonstration of the capability to image an Earth-like extrasolar planet," Nature 446, 771-773 (2007).
[CrossRef] [PubMed]

Proc. SPIE (6)

D. W. Wilson, P. D. Maker, J. T. Trauger, and T. B. Hull, "Eclipse apodization: realization of occulting spots and Lyot masks," Proc. SPIE 4860, 361-370 (2003).
[CrossRef]

P. G. Halverson, M. Z. Ftaclas, K. Balasubramanian, D. J. Hoppe, and D. W. Wilson, "Measurement of wavefront phase delay and optical density in apodized coronagraphic mask materials," Proc. SPIE 5905, 59051I (2005).
[CrossRef]

J. T. Trauger, C. Burrows, B. Gordon, J. Green, A. Lowman, D. Moody, A. Niessner, F. Shi, and D. Wilson, "Coronagraph contrast demonstrations with the high contrast imaging testbed," Proc. SPIE 5487, 1330-1336 (2004).
[CrossRef]

K. Balasubramanian, D. W. Wilson, R. E. Muller, B. D. Kern, and E. Sidick, "Thickness dependent optical properties of metals and alloys applicable to TPF coronagraph image masks," Proc. SPIE 6693, 66930Z (2007).
[CrossRef]

D. C. Moody and J. T. Trauger, "Hybrid Lyot coronagraph masks and wavefront control for improved spectral bandwidth and throughput," Proc. SPIE 6693, 66931I (2007).
[CrossRef]

E. Sidick and K. Balasubramanian, "Effects of optical-density and phase dispersion of an imperfect band-limited occulting mask on the broadband performance of a TPF coronagraph," Proc. SPIE 6693, 66931C (2007).
[CrossRef]

Other (7)

A thin film design software from Thin Film Center, Inc., Tucson, Ariz., USA.

G. Hass and L. Hadley, Optical Properties of Metals (AIP Handbook, 1972), pp. 6-124.

www.specialmetals.com; also, www.espi.com.

Canyon Materials, Inc., San Diego, Calif., USA, http://canyonmaterials.com.

K. Balasubramanian, D. J. Hoppe, P. G. Halverson, D. W. Wilson, P. M. Echternach, F. Shi, A. E. Lowman, A. F. Niessner, J. T. Trauger, and S. B. Shaklan, "Occulting focal plane masks for terrestrial planet finder coronagraph--design, fabrication, simulations and test results," in Proceedings of IAU Colloquium 200, Direct Imaging of ExoPlanets (Cambridge U. Press, 2006), pp. 405-409.

JPL web site on Planet Quest: http://planetquest.jpl.nasa.gov/TPF/tpflowbarindex.cfm.

V. Lucarini, J. J. Saarinen, K. E. Peiponen, and E. M. Vartiainen, Kramers-Kronig Relations in Optical Materials Research (Springer-Verlag, 2005).

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Figures (16)

Fig. 1
Fig. 1

(Color online) (a) Typical 1D gray-scale mask transmission image and (b) cross-section transmittance and OD profiles.

Fig. 2
Fig. 2

(Color online) Measured OD versus e-beam dose of a HEBS glass mask material at 830, 785, 635, and 532   nm wavelengths.

Fig. 3
Fig. 3

(Color online) Measured phase advance versus OD of a HEBS glass mask material at 830, 785, 635, and 532   nm wavelengths. Here, phase advance refers to the difference in transmitted light phase between a region of the material exposed to the e-beam and a region that is not exposed to the e-beam. Positive values on the chart mean that the light wave advances relative to the unexposed region, while negative values mean a delay.

Fig. 4
Fig. 4

(Color online) Concept of a profiled metallic mask; relative step heights can be made small to approximate a continuous profile. A typical transmittance profile is of the form T = [ 1 sin c 2 ( x ) ] 2 .

Fig. 5
Fig. 5

Definition of OD and phase differences through the mask, where b refers to a bias region on the mask, which may be the blank substrate, and λ 0 is the center wavelength within a chosen band.

Fig. 6
Fig. 6

(Color online) Refractive index n (solid curves) and extinction coefficient k (dashed curves) of some common metals. Source: Thin Film Center Inc., materials data provided with their essential macleod [14] thin film design software package.

Fig. 7
Fig. 7

(Color online) ( n 1 ) / λ (solid curves) and k / λ (dashed curves) of some common metals.

Fig. 8
Fig. 8

(Color online) Calculated OD versus thickness of Ni, Cr, Pt, and Inconel 600 films. Cr shows the maximum OD spread among these materials. Each subplot above contains 11 curves covering the 500 1000   nm wavelength band in steps of 50   nm . The bias region in this case is blank fused silica substrate with no metal film.

Fig. 9
Fig. 9

(Color online) Calculated OD dispersion versus center wavelength OD of metal films on fused silica substrate. Data from Fig. 8 is used to calculate these. Each panel includes 11 curves corresponding to wavelengths from 700 to 800   nm in 10   nm steps. The bias region in this case is blank fused silica substrate with no metal film.

Fig. 10
Fig. 10

(Color online) Calculated transmitted phase versus thickness of Ni, Cr, Pt, and Inconel600 films. Each subplot above contains 11 curves covering the 500 1000   nm wavelength band in steps of 50   nm . The bias region in this case is blank fused silica substrate with no metal film. The “hockey-stick-like” character is a consequence of interference effects in the small thickness range. Note that the calculations assumed no thickness dependence of the complex refractive index; in reality, thickness dependence of optical constants is expected.

Fig. 11
Fig. 11

(Color online) Phase dispersion versus center wavelength OD of metal films on fused silica substrate from the same data presented in Fig. 10. Each panel includes 11 curves corresponding to wavelengths from 700 800   nm in 10   nm steps. Note that the center wavelength phase, which represents a reference in these plots, still has the nonzero phase relationship with thickness (or OD) as seen in Fig. 10.

Fig. 12
Fig. 12

(Color online) Conceptual metallic mask layer structure to optimize OD and phase neutrality; exaggerated step geometry is shown for clarity. Finer steps will produce a nearly continuous profile. The dielectric layer thickness at each point can be optimized for the specific metal layer thickness to compensate for the phase delay caused by the metal layer.

Fig. 13
Fig. 13

(Color online) Required dielectric film thickness to correct the center wavelength phase caused by the mask layer; in this example, PMMA is employed for the correction layer.

Fig. 14
Fig. 14

(Color online) Residual phase dispersion versus center wavelength OD of metal films on fused silica substrate after correcting the center wavelength phase with a dielectric layer as per thicknesses shown in Fig. 13. Each panel includes 11 curves corresponding to wavelengths from 700 800   nm in 10   nm steps. Note that the correction of center wavelength phase results in a slightly larger dispersion with different characteristics as above in comparison with Fig. 11.

Fig. 15
Fig. 15

(Color online) (a) Ni film OD and (b) Δ OD versus protective overcoat optical thickness.

Fig. 16
Fig. 16

(Color online) OD dispersion of Ni layer with (a) 100   nm and (b) 285   nm SiO 2 protective layer in the 700 800   nm band showing the shifting of zero crossing and minimizing region.

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

OD = f ( t , λ ) .
k / λ constant .
ϕ = f ( t , λ ) = 2 π ( n n 0 ) t / λ .
( n n 0 ) / λ constant ,

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