All Figures

$\begin{figure} \par\includegraphics[height=5.5cm]{8473f1.eps}\end{figure}$ Figure 1: Schematic layout of the collimated configuration. A frequency-stabilized He-Ne laser, a spatial filter and a collimator (not shown in the figure) produce a collimated beam that a first diaphragm (D1) reduces to 30 mm in diameter. After the Fabry-Perot interferometer, a lens (L) reduces the beam to the dimensions of the CCD camera, where each pixel corresponds to a small area of the interferometer plates, illuminated by a normally incident collimated raybundle (green line). The D2 diaphragm eliminates spurious light due to reflections on the rear surfaces of the interferometer plates.
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In the text

$\begin{figure} \par\includegraphics[width=14cm]{8473f2.eps}\end{figure}$ Figure 2: Maps of the measured FWHM ( left column) and profile width ratio ( right column) for FPI #1 ( a, b) and FPI #2 ( c,d). The FWHM maps are scaled between 0.8 and 1.4 times the median value of the FWHM for each FPI (see Fig. 3), while the width ratios are scaled between values of 7 and 11. The tick marks are at a 1 mm spacing and the maps cover a total diameter of 30 mm.
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In the text

$\begin{figure} \par {\includegraphics[width=7cm,height=7cm]{8473f3.eps} } \end{figure}$ Figure 3: Averaged histograms of the FWHM measured from the pixel profiles for each interferometer. Solid and dashed lines refer to FPI #1 and FPI #2 respectively. The histograms are averaged over all the collimated scans listed in Table 3. Lighter lines are the histograms of the individual scans that went into the averages. Abscissae are plotted both relative to the median FWHM and in terms of the actual profile width for each FPI.
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In the text

$\begin{figure} \par {\includegraphics[width=7cm,height=6cm]{8473f4.eps} } \end{figure}$ Figure 4: Averaged histograms of the width ratios measured from the pixel profiles for each of the two interferometers. Solid and dashed lines refer to FPI #1 and FPI #2 respectively. Lighter lines show the histograms of the individual scans that went into the averages for each FPI. The vertical dotted line indicates the width ratio expected for an Airy profile.
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In the text

$\begin{figure} \par\includegraphics[width=16.5cm]{8473f5.eps}\end{figure}$ Figure 5: Model curves calculated from an Airy function T for a given reflectivity (Eq. (2)) convolved with a Gaussian distribution of width $\sigma _\lambda$ (mÅ) such that the FWHM of the resulting profile properly matches the observed median value of the FWHM. The width ratio and peak transmission (for three different values of A) are determined for each convolved profiled. Solid and dashed lines refer to FPI #1 and FPI #2 respectively. Left: reflectivity and $\sigma _\lambda$ plotted against the width ratio. The vertical dotted line indicates the measured width ratio for both FPI. Right: peak transmission for three different values of the absorption coefficient A (0.001, 0.002, 0.003) versus width ratio. The vertical dotted line is the same as that on the left, while the two horizontal lines indicate the measured mean peak transmission for FPI #1 ( solid line) and FPI #2 ( dashed line).
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In the text

$\begin{figure} \par\includegraphics[width=13.5cm]{8473f6.eps}\end{figure}$ Figure 6: Maps of the measured wavelength shifts of the pixel profiles ( a), c)) and of the same shifts after removal of the plate non-parallelism and the fitted Zernike polynomials ( b), d)), for FPI #1 ( top) and FPI #2 ( bottom). For all the images, shifts are scaled between $\pm~$ 25 Å (red positive) of spacing variation, or $\pm~$ 7 mÅ of profile shifts for FPI #1 and $\pm~$ 25 mÅ of profile shifts for FPI #2.
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In the text

$\begin{figure} \hbox{ \resizebox{8.8cm}{!}{\includegraphics{8473f7a.eps}} } \hbox{ \resizebox{8.8cm}{!}{\includegraphics{8473f7b.eps}} } \end{figure}$ Figure 7: The mean profiles from the collimated configuration for FP #1 ( top) and FP #2 ( bottom) for an illuminated area of 30 mm. The profiles were averaged after removing only the large-scale errors, leaving the profile broadened by the random spacing variations. The dotted lines shows the convolution of an Airy function defined by the measured interferometer reflectivity (FP #1: 0.935; FP #2: 0.931) and a Gaussian function with the measured $\sigma$ (FP #1: 8.8 Å; FP #2: 9.1 Å). The lower part of each plot shows the differences between the observed and calculated profiles (including error bars for the measured profile of FP #1). All the profiles have been normalized to a peak intensity of unity.
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In the text

$\begin{figure} \hbox{ \hglue -0.0cm \resizebox{8.8cm}{!}{\includegraphics{8473f8... ...\hglue -0.0cm \resizebox{8.8cm}{!}{\includegraphics{8473f8b.eps}} } \end{figure}$ Figure 8: As Fig. 7, but the profiles were averaged after removing only the plate non-parallelism errors, leaving the profile broadened by all inherent plate spacing variations over the central 30 mm diameter.
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In the text

$\begin{figure} \par\includegraphics[height=5.9cm]{8473f9.eps}\end{figure}$ Figure 9: Schematic layout of the telecentric configuration. A frequency-stabilized He-Ne laser (not shown in the figure) illuminates a flashed opal diffuser which simulates a monochromatic incoherent source. The laser light from the diffuser is collimated by a first lens (L1), while two other lenses, after the Fabry-Perot, form an image of the interferometer plates on the CCD camera. In this case, each pixel corresponds to a small area of the plates illuminated by a normally incident cone of rays, containing all the possible directions allowed by the optics.
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In the text

$\begin{figure} \par\mbox{ \includegraphics[width=7cm]{8473f10a.eps}\hspace*{0.8cm} \includegraphics[width=7cm]{8473f10b.eps} } \end{figure}$ Figure 10: Surface representation of the Zernike polynomials that were fitted to the cavity errors measured for FP #1 ( left) and FP #2 ( right) in the telecentric configuration. The circles plotted in the x-y plane and the corresponding contours on the surfaces have diameters of 33 mm (the illuminated area for IBIS) and 40 mm.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{8473f11.eps}}\end{figure}$ Figure 11: Histogram of plate spacing fluctuations (Å) for FP #1 over the central 45 mm of the interferometer ( solid line), as determined by convolving the distribution of separations in the fitted Zernike polynomials ( dotted line) with a Gaussian distribution with a width $\sigma _{t}^{r}$ as given in Table 4. For comparison, the similarly derived distribution for a 30 mm aperture (see Sect. 3.4) is also shown ( dashed line).
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics{8473f12.eps}}\end{figure}$ Figure 12: As Fig. 11 for FP #2.
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In the text

$\begin{figure} \par\includegraphics[height=5.8cm]{8473f13.eps}\end{figure}$ Figure 13: Schematic layout of the classic configuration. The layout is similar to that of Fig. 9, but with the CCD camera at the focus of the lens L2, where an image of the diffuser is formed. In this case, each pixel corresponds to a collimated beam incident with a given angle on the interferometer plates.
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In the text

$\begin{figure} \hbox{ \resizebox{8.8cm}{!}{\includegraphics{8473f14a.eps}} } \hbox{ \resizebox{8.8cm}{!}{\includegraphics{8473f14b.eps}} } \end{figure}$ Figure 14: The mean profiles from the classic configuration for FPI #1 ( top) and FPI #2 ( bottom). The profiles were averaged after removing the instrumental blue-shift, leaving them broadened by all inherent plate spacing variations. The dotted line shows the convolution of an Airy function defined by the derived interferometer reflectivity (FPI #1: 0.935; FPI #2: 0.931) and the full distribution of spacing errors measured on a 45 mm aperture in telecentric configuration. The lower part of each plot shows the differences between the measured and calculated profiles. All the profiles were normalized to a peak intensity of unity.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{8473f15.eps}}\end{figure}$ Figure 15: Plots showing the variations of several parameters of the instrumental profile at the 6328 Å as a function of the total illuminated diameter on the interferometers in a dual FPI system using a classic mount. The FWHM and equivalent width are given in mÅ. The profile ratio is calculated from the relative contribution of two halves of the profile on either side of the peak intensity (see Eq. (6)). The vertical dotted line indicates the illuminated diameter for IBIS and the dashed line in the middle panel shows the equivalent width of the combined profile in the case that the FPI were absent of any plate defects.
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In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{8473f16.eps}}\end{figure}$ Figure 16: The mean profile ( solid line) from the measurement of the transmission profile through FPI #1 and FPI #2 in series. The profile, averaged after removing the instrumental blue-shift, was measured over an area of 35 mm on the interferometers. The dotted line shows the calculated multi-etalon profile using Eq. (5), while the lower plot shows the difference between the measured and calculated profiles. The observed profile has been normalized to the peak intensity of the calculated profile.
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In the text

$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{8473f17.eps}}\end{figure}$ Figure 17: The coating reflectivity of the interferometer plates as a function of wavelength. The solid line shows the reflectivity curve provided by the manufacturer, while the dotted and dashed line show this curve for FPI #1 and FPI #2 respectively, after being shifted to match the values of the reflectivity found at the laser wavelength ( vertical line).
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In the text

$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{8473f18.eps}}\end{figure}$ Figure 18: The FWHM of the IBIS instrumental profile vs. wavelength. The crosses indicate the wavelengths of several currently available interference filters (Paper I). The diagonal dashed lines show contours of constant spectral resolving power ( $\lambda / {\it FWHM}$ ), indicating IBIS achieves a resolution of close to 300 000 over most of its wavelengths range below 7300 Å.
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In the text

$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{8473f19.eps}}\end{figure}$ Figure 19: The parasitic light of the IBIS instrumental profile vs. wavelength. This quantity has been calculated by supposing in series with the two FPI a theoretical two-cavity interference filter, with a FWHM of 3 Å (solid line) and 5 Å (dashed line). Crosses indicate the wavelengths of several currently available interference filters for IBIS.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics{8473f20.eps}}\end{figure}$ Figure 20: The wavelength range around the central transparency peak which encloses 95% of the entire energy transmitted by the instrumental profile, vs. wavelength. The enclosed energy range was calculated by supposing in series with the two FPI a theoretical two-cavity interference filter, with a FWHM of 3 Å (solid line) and 5 Å (dashed line). Crosses indicate the wavelengths of several currently available interference filters for IBIS. The dotted line shows the FWHM of the transmission profile (as in Fig. 18), which by comparison typically encloses approximately 65% of the overall transmittance.
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics{8473f21.eps}}\end{figure}$ Figure 21: Top: The effect of the instrumental profile on the synthetic Fe I 7090 Å spectral line profile. The deepest line is the average profile from the simulations. The shallower red and blue lines are the averages after convolution with the instrumental profile for the nominal FPI parameters (R=0.952, flatness = $\lambda /168$ at 7090 Å) and for the full 45 mm interferometer aperture. All profiles are normalized to the continuum intensity at 7090.1 Å. Bottom: The difference between the average synthetic spectral line and the average line after convolution with the nominal profile ( solid line) as well as the difference between the profiles resulting from the convolution of the nominal and 45 mm aperture instrumental profile ( dotted line).
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In the text

$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics{8473f22.eps}}\end{figure}$ Figure 22: Similar to Fig. 21, except examining the effect of the instrumental profile on the Stokes V profile. Top: A synthetic Stokes V profile for the 6301.5 Å and 6302.5 Å spectral lines unconvolved by any instrumental profile ( solid line) together with the Stokes V profile determined after convolving the measured I+V and I-V spectra with the nominal ( red) and 45 mm aperture ( blue) instrumental profiles. Bottom: The difference between the synthetic Stokes V profile and the Stokes V profile calculated after the convolution with the nominal instrumental profile ( solid line) and the difference between the Stokes V profiles resulting from the convolution of the nominal and 45 m aperture instrumental profile ( dotted line).
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In the text

$\begin{figure} \par\includegraphics[width=14cm]{8473f2.eps}\end{figure}$	Figure 2: Maps of the measured FWHM ( left column) and profile width ratio ( right column) for FPI #1 ( a, b) and FPI #2 ( c,d). The FWHM maps are scaled between 0.8 and 1.4 times the median value of the FWHM for each FPI (see Fig. 3), while the width ratios are scaled between values of 7 and 11. The tick marks are at a 1 mm spacing and the maps cover a total diameter of 30 mm.
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$\begin{figure} \par {\includegraphics[width=7cm,height=6cm]{8473f4.eps} } \end{figure}$	Figure 4: Averaged histograms of the width ratios measured from the pixel profiles for each of the two interferometers. Solid and dashed lines refer to FPI #1 and FPI #2 respectively. Lighter lines show the histograms of the individual scans that went into the averages for each FPI. The vertical dotted line indicates the width ratio expected for an Airy profile.
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$\begin{figure} \hbox{ \hglue -0.0cm \resizebox{8.8cm}{!}{\includegraphics{8473f8... ...\hglue -0.0cm \resizebox{8.8cm}{!}{\includegraphics{8473f8b.eps}} } \end{figure}$	Figure 8: As Fig. 7, but the profiles were averaged after removing only the plate non-parallelism errors, leaving the profile broadened by all inherent plate spacing variations over the central 30 mm diameter.
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$\begin{figure} \par\mbox{ \includegraphics[width=7cm]{8473f10a.eps}\hspace*{0.8cm} \includegraphics[width=7cm]{8473f10b.eps} } \end{figure}$	Figure 10: Surface representation of the Zernike polynomials that were fitted to the cavity errors measured for FP #1 ( left) and FP #2 ( right) in the telecentric configuration. The circles plotted in the x-y plane and the corresponding contours on the surfaces have diameters of 33 mm (the illuminated area for IBIS) and 40 mm.
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$\begin{figure} \par\resizebox{8.5cm}{!}{\includegraphics{8473f12.eps}}\end{figure}$	Figure 12: As Fig. 11 for FP #2.
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$\begin{figure} \par\includegraphics[height=5.8cm]{8473f13.eps}\end{figure}$	Figure 13: Schematic layout of the classic configuration. The layout is similar to that of Fig. 9, but with the CCD camera at the focus of the lens L2, where an image of the diffuser is formed. In this case, each pixel corresponds to a collimated beam incident with a given angle on the interferometer plates.
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$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{8473f17.eps}}\end{figure}$	Figure 17: The coating reflectivity of the interferometer plates as a function of wavelength. The solid line shows the reflectivity curve provided by the manufacturer, while the dotted and dashed line show this curve for FPI #1 and FPI #2 respectively, after being shifted to match the values of the reflectivity found at the laser wavelength ( vertical line).
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$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{8473f18.eps}}\end{figure}$	Figure 18: The FWHM of the IBIS instrumental profile vs. wavelength. The crosses indicate the wavelengths of several currently available interference filters (Paper I). The diagonal dashed lines show contours of constant spectral resolving power ( $\lambda / {\it FWHM}$ ), indicating IBIS achieves a resolution of close to 300 000 over most of its wavelengths range below 7300 Å.
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$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{8473f19.eps}}\end{figure}$	Figure 19: The parasitic light of the IBIS instrumental profile vs. wavelength. This quantity has been calculated by supposing in series with the two FPI a theoretical two-cavity interference filter, with a FWHM of 3 Å (solid line) and 5 Å (dashed line). Crosses indicate the wavelengths of several currently available interference filters for IBIS.
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