Multiple-Star System Adaptive Vortex Coronagraphy Using a Liquid Crystal Light Valve

We propose the development of a high-contrast imaging technique enabling the simultaneous and selective nulling of several light sources. This is done by realizing a reconfigurable multiple-vortex phase mask made of a liquid crystal thin film on which local topological features can be addressed electro-optically. The method is illustrated by reporting on a triple-star optical vortex coronagraphy laboratory demonstration, which can be easily extended to higher multiplicity. These results allow considering the direct observation and analysis of worlds with multiple suns and more complex extrasolar planetary systems.

Figure 1

(a) Localized vortex mask setup. $I$, iris; PO, polarization optics; $L$ and $L^{\prime }$, lenses; LCLV, liquid crystal light valve; Cam,camera; $U$, quasistatic applied voltage. (b) Image under crossed circular polarizers (XCPOL) of the sample illuminated by a uniformly illuminated circular-shaped mask beam at 532 nm wavelength. (c) Same as panel (b) but in the case of crossed linear polarizers (XPOL). Panels (d) and (e) are the simulated counterparts of panels (b) and (c) assuming an axisymmetric retardance profile.

Figure 2

Multiple-star vortex coronagraph laboratory demonstration setup. $W_i$, writing beams generating on-demand localized vortex masks; $S_i$, starlight beams mimicking pointlike sources; $I_i$, irises; $L_i$, lenses with focal length $f_i$; $CP$, CA, circular polarizer and analyzer; UBS, unpolarized beamsplitter; $F$, Notch filter at 532 nm; Cam, camera. Light sources are mutually incoherent.

Figure 3

(a) Azimuth-averaged angular intensity distribution when the single-star coronagraph is off (black curves) and on (red curves) as a function of the reduced angular coordinate $\alpha /{\alpha }_{\text{diff}}$. Thick curves: experimental data; thin curves: simulations. (b) Ring of fire in the exit pupil plane. Experimental reimaged pointlike sources when the coronagraph is off and on are shown on panels (c) and (d) with $I_0$ being the maximal intensity in the off state and where the logarithmic intensity range refers to the 4096 camera levels. The incident starlight is right-handed circularly polarized.

Figure 4

(a) Airy spots of a triple-star system ($S_1$, $S_2$, $S_3$) in the focal plane of the telescope. (b) XPOL focal plane image of the corresponding vortex masks ($M_1$, $M_2$, $M_3$) generated by the writing beams ($W_1$, $W_2$, $W_3$) where the dashed circles indicate the contours of the illumination disks.

Figure 5

Optical vortex coronagraphy laboratory demonstration of a system that consists of a triple star plus a planet. Reimaged light sources ($S_1$, $S_2$, $S_3$) and planet $P$ with lens $L_4$ of focal length $f_4=500\mathrm{mm}$ when the coronagraph is off (a) and on (b) with $I_{\max }$ being the maximal intensity of each image and where the logarithmic intensity range refers to the 4096 camera levels. Note that higher noise level in panel (b) results from limited exposure time of the camera, which limits the dynamic range of the image. The incident starlight is right-handed circularly polarized. The simulated counterparts of panels (a) and (b) are shown on panels (c) and (d).