Muamer Zukic

Vacuum ultraviolet thin films. 1: Optical constants of BaF 2 , CaF 2 , LaF 3 , MgF 2 , Al 2 O 3 , HfO 2 , and SiO 2 thin films

The optical constants of MgF(2) (bulk) and BaF(2), CaF(2), LaF(3), MgF(2), Al(2)O(3), HfO(2), and SiO(2) films deposited on MgF(2) substrates are determined from photometric measurements through an iteration process of matching calculated and measured values of the reflectance and transmittance in the 120-230-nm vacuum ultraviolet wavelength region. The potential use of the listed fluorides and oxides as vacuum ultraviolet coating materials is discussed in part 2 of this paper.

Vacuum ultraviolet thin films. 2: Vacuum ultraviolet all-dielectric narrowband filters

We report the design and performance of narrowband transmission filters employing the rapidly changing extinction coefficient that is characteristic of BaF(2) and SiO(2) films within certain wavelength intervals in the vacuum ultraviolet. We demonstrate the design concept for two filters centered at 135 nm for BaF(2) and at 141 nm for SiO(2). It is found that these filters provide excellent narrowband spectral performance when combined with narrowband reflection filters. The filter centered at 135 nm has a peak transmittance of 24% and a bandwidth of 4 nm at full width at half-maximum for collimated incident light. The transmittance for lambda(0) </= 130 nm is <0.1% and for 138 </= lambda(0) </= 230 nm the average transmittance is <3%. Another filter centered at 141 nm has a peak transmittance of 25% and a bandwidth of 3.5 nm.

Multiple reflectors as narrow-band and broadband vacuum ultraviolet filters

We report on the development of a new coating design for applications in the vacuum ultraviolet that yields significantly higher reflectivity over selectable bandwidths. We demonstrate that the concept can be used to fabricate high-performance narrow-band and broadband reflection filters, whose spectral properties can be greatly enhanced by utilizing several of these filters in tandem. For example, we have fabricated a narrow-band filter at the location of the 0 I 135.6-nm line with a 3.2-nm bandwidth, a peak transmittance of 39.3%, and out-of-band wavelength blocking of better than 10(-4)%. The principle of ourdesign approach is to use a combination of high (H) and low (L) refractive-index dielectric pairs so that H + L = lambda(r)/2, where H/L < 1. H and L designate the optical thicknesses of high- and low-index film materials. This kind of choice for the high-low ratio reduces the effects of absorption for the H films for which the extinction coefficient in the vacuum ultraviolet is much higher than for the low-index film material MgF(2). The reduced absorption of multilayers with H/L < 1 results in a significant increase in reflectivity compared with the classical quarter-wave stack for which H/L = 1.

Filters for the International Solar Terrestrial Physics Mission far-ultraviolet imager

The far-ultraviolet (FUV) imager for the International Solar Terrestrial Physics (ISTP) Mission is designed to image four features of the aurora: O I lines at 130.4 and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 and 160 nm (LBH long) and 160 and 180 nm (LBH long). We report the design and fabrication of narrowband and broadband filters for the ISTP FUV imager. Narrowband filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 23.9 and 38.3% at 130.4 and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance close to 60%. Blocking of out-of-band wavelengths for all filters is better than 5 x 10-3% with the transmittance at 121.6 nm of less than 10-6%.

Depth profiling analysis of aluminum oxidation during film deposition in a conventional high vacuum system

The oxidation of aluminum thin films deposited in a conventional high vacuum chamber has been investigated using x‐ray photoelectron spectroscopy (XPS) and depth profiling. The state of the Al layer was preserved by coating it with a protective MgF2 layer in the deposition chamber. Oxygen concentrations in the film layers were determined as a function of sputter time (depth into the film). The results show that an oxidized layer is formed at the start of Al deposition and that a less extensively oxidized Al layer is deposited if the deposition rate is fast. The top surface of the Al layer oxidizes very quickly. This top oxidized layer may be thicker than has been previously reported by optical methods. Maximum oxygen concentrations measured by XPS at each Al interface are related to pressure to rate ratios determined during the Al layer deposition.

Design and fabrication of multilayer reflective filters for a Ritchey-Chretien Lyman-alpha telescope

We report the design and fabrication of multilayer reflective filters for the self-filtering cameras of a Ritchey-Chretien Lyman-a (Ly-a) telescope that uses reflecting multilayer mirrors, polarizers, and filters. The Ly-a telescope is designed to measure the linear polization of hydrogen Ly-a line (121.6 nm) emissions from the solar corona. A key element of the filter design includes the development of p multilayers optimized to provide maximum reflectance at 121.6 nm for the respective cameras without significant angular variation from 0 to 15-deg incident angles. We applied self-filtering concepts to design Ly-a telescope filters that are composed of two reflective mirrors. The calculated value of the net throughput is 28.38% with a 4-nm bandwidth at a center wavelength of 121.6 nm. The measured value is 27.35% with a less than 6-nm bandwidth at incidence angle 10 deg.

Ultraviolet imager for the International Solar Terrestrial Physics mission

Imaging of the earths auroral regions in the ultraviolet provides information on a global scale on the energy flux and characteristics of precipitating particles an on the composition of the atmosphere in which the energy is deposited. The authors report the design of an imager with 0.6-mrad angular resolution over an 8-deg field of view sampled with 39,500 pixels, yielding global auroral coherent imaging from above 6 R[sub E](Earth radii). High-performance filters provide spectrally pure measurements of four key far-UV (FUV) features, with 5 [times] 10[sup [minus]5] out-of-band rejection. Together with a solar blind intensified CCD detector, a net rejection of 10[sup [minus]9] of all out-of-band emissions is achieved. The optical design comprises a three-mirror f/3 system that yields a noise equivalent sensitivity of 10 rayleighs (R) for a 37-s frame rate. The intrascene and interscene dynamic ranges are 1,000 and 10[sup 5], respectively. The optical surface microroughness is less than 2 nm, providing exceptionally low light scattering characteristics, allowing simultaneous observations of very weak and bright emissions. The imager should provide about two orders of magnitude improvement in performance over previous designs.

Polarimetry of H-Lyman α for coronal magnetic field diagnostics

We discuss and analyze the possible sources of observational and instrumental uncertainty that can be encountered in measuring magnetic fields of the solar corona through polarimetric observations of the Hanle effect of the coronal Ly-alpha line. The Hanle effect is the modification of the linear polarization of a resonantly scattered line, due to the presence of a magnetic field. Simulated observations are used to examine how polarimetric measurements of this effect are affected by the line-of-sight integration, the electron collisions, and the Ly-alpha geocorona. We plan to implement the coronal magnetic field diagnostics via the Ly-alpha Hanle effect using an all-reflecting Ly-alpha coronagraph/polarimeter (Ly-alphaCoPo) which employs reflecting multilayer mirrors, polarizers, and filters. We discuss here the requirements for such an instrument, and analyze the sources of instrumental uncertainty for polarimetric observations of the coronal Ly-alpha Hanle effect. We conclude that the anticipated polarization signal from the corona and the expected performance of the Ly-alphaCoPo instrument are such that the Ly-alpha Hanle effect method for coronal field diagnostics is feasible.

Stray light analysis of a reflecting UV Coronagraph/Polarimeter with multilayer optics

An analysis is presented of the stray light expected in a Coronagraph/Polarimeter operating at the H I Lyman (alpha) (Ly-(alpha) ) line ((lambda) 121.6 nm) and utilizing multilayer interference film optics and ultrasmooth substrates (i.e., rms-smoothness Optics & Photonics OP 40 1993-07-11|1993-07-16 SPIEs 1993 International Symposium on Optics, Imaging, and Instrumentation SD93 51144 San Diego, CA, United States X-Ray and Ultraviolet Polarimetry 2010 Astronomical XUV Polarimetry II 2

Extreme ultraviolet filters for 58.4 and 83.4 nm

We report the design of an extreme ultraviolet (EUV) filter for He I at 58.4 nm and the design and fabrication of an EUV filter for O II at 83.4 nm. Both filters are designed as combinations of three narrow-band reflection filters. The net transmittance through both EUV filters is close to 10% with bandwidths less than 10 nm, and blocking better than 0.005% for out-of-band wavelengths. A theoretical calculation of the 83.4 nm filter predicts higher values for the peak transmittance than the measured spectral performance of the fabricated filter. Since aluminum is one of the film materials used for the fabrication of EUV filters, the aluminum film oxidation can be modeled in order to explain the discrepancy between the theory and experiment. The 83.4 nm filters were deposited in a conventional high vacuum coater with pressure of 10-6 torr. In order to avoid aluminum oxidation and improve the performance of the narrow-band filters, an ultrahigh vacuum coater must be used with deposition pressures of less than 10-10 torr. Since the filters operate at angles of incidence up to 50 degree(s), the optical components of a system can serve as both the filtering and imaging elements.