Abstract
Exoplanets around multiple-star systems are interesting targets for direct detection. However, it is difficult to suppress unwanted light from all stars in a system. For direct detection of ...the exoplanets around multiple-star systems, we propose using common-path visible nulling coronagraphs (CP-VNCs). CP-VNCs can suppress diffracted light from stars located on a central null fringe. In addition, a wave front control system is installed to generate a dark hole by rejecting residual stellar speckles of CP-VNCs. For this purpose, spatial light modulators (SLMs) have the ability to generate a dark hole over a wide field on the order of hundreds of
λ
/
D
(where
λ
is the wavelength of light and
D
is the telescope diameter), owing to their large number of pixels. We perform a laboratory demonstration of high-contrast observation around a binary-star system model using a CP-VNC combined with an SLM. First, we simulate a high-contrast observation over a region close to one of two stars by generating a square dark hole with side lengths of 40
λ
0
/
D
(where
λ
0
is the central wavelength of the light sources). The center of the square region was located about 35
λ
0
/
D
and 79
λ
0
/
D
from each star. Measurements of this first scenario find a mean contrast over the dark hole of 3.5 × 10
−8
. Second, observation of a region with identical separation (100
λ
0
/
D
) from both stars is also demonstrated. In this scenario, a mean contrast of 2.0 × 10
−8
is achieved over a circular dark hole with a diameter of 40
λ
0
/
D
.
Abstract
High-contrast instruments are required for direct imaging of faint exoplanets around bright host stars. In high-contrast instruments, a wave front control system is needed to generate a dark ...hole by suppressing residual stellar speckles. However, the achievable contrast is limited by the phase quantization error (i.e., finite phase resolution) of wave front control devices, such as deformable mirrors or spatial light modulators. In this paper, we propose a halftone method for wave front control to improve the contrast using a wave front control device with quantized phase modulation. In a numerical simulation, the contrast was improved from 1.4 × 10
−9
to 3.8 × 10
−10
by halftone wave front control. In addition, we performed a laboratory demonstration in which a spatial light modulator was used for wave front control, and the contrast was improved from 2.2 × 10
−7
to 6.0 × 10
−8
for a phase resolution of 2
π
/256.
Abstract
Direct detection of exoplanets requires a high-contrast instrument called a coronagraph to reject bright light from the central star. However, a coronagraph cannot perfectly reject the ...starlight if the incoming stellar wave front is distorted by aberrations due to the Earth’s atmospheric turbulence and/or the telescope instrumental optics. Wave-front aberrations cause residual stellar speckles that prevent detection of faint planetary light. In this paper, we report a laboratory demonstration of a speckle-nulling wave-front control using a spatial light modulator (SLM) to suppress the residual speckles of a common-path visible nulling coronagraph. Because of its large format, the SLM potentially has the ability to generate a dark hole over a large region or at a large angular distance from a star of up to hundreds of
λ
/
D
. We carry out a laboratory demonstration for three cases of dark hole generation: (1) in an inner region (3–8
λ
/
D
in horizontal and 5–15
λ
/
D
in vertical directions), (2) in an outer region (70–75
λ
/
D
in horizontal and 65–75
λ
/
D
in vertical directions), and (3) in a large region (5–75
λ
/
D
in both directions). As a result, the residual speckles are rejected to contrast levels on the order of 10
−8
in cases 1 and 2. In cases 2 and 3, we can generate dark holes at a large distance (up to >100
λ
/
D
) and with a large size (70
λ
/
D
square), both of which are out of the Nyquist limit of currently available deformable mirrors.
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