Overview
Omega Optical designs and manufactures custom filters and standard prescription filters to the highest imaging quality standards for astronomers, atmospheric scientists, and aerospace instrumentation companies worldwide. Applications include both terrestrial and space-based observational instruments. We have supplied projects and programs for a wide variety of prestigious universities, observatories, government agencies, and international consortia. As instrument technologies and applications evolve, we work collaboratively with customers to develop solutions for the spectral, optical, and environmental demands that will define observational astronomy and aerospace applications in the future.
High Spectral Performance
We provide interference passband filters with peak wavelengths located from the UV to the mid-IR and with bandwidths ranging from 0.15nm to several hundred nanometers wide. Our filters meet demanding throughput and bandshape requirements while adhering to very close tolerances on bandwidth and peak transmission wavelength. Many of our filters are designed for high attenuation of adjacent emission lines. Our coating processes assure uniformity of spectral performance over the physical area of large filters.
High Optical Performance
Our filters are made to rigorous imaging requirements. We start by polishing optical glasses to requisite flatness and wedge values prior to coating and assembly. By designing each coating for the longest free spectral range, we minimize the number of laminations that cause internal reflection and fringe patterns. After assembly, our filters are polished to achieve minimum wavefront distortion. We can evaluate wavefront properties using the Shack-Hartmann wavefront sensor and/or the Broadband Achromatic Twyman-Green interferometer, when needed. Durable anti-reflective coatings are deposited on outer surfaces to increase transmission and reduce ghosting.
Physical Attributes
Hubble TelescopeMany of our astronomy filters are made in sets or as supplements to existing sets. Each filter is designed to match the others in attributes such as optical thickness, bandshape, throughput, attenuation, sensitivity to system focal ratio, sensitivity to temperature, and imaging quality. Continuum filter sets are made with precise matching of the cut-on and cut-off wavelengths of spectrally adjacent filters. Spacebased application filters are manufactured using “space-flight compatible” materials.
Custom Filters & Sets
Many astronomy imaging applications require the custom design and manufacture of filters and filter sets. With more than twenty vacuum deposition systems—including IAD, electron beam, plasma assisted reactive magnetron sputtering (PARMS) and multi-planet coating technologies—we are able to produce filters of extreme uniformity and precision in quantities of one to one thousand according to the following general specifications:
- Wavelength Range: UV to mid IR
- Bandwidths: 0.15 nm to several hundred nm
- Tolerances: Critical throughput, bandshape and bandwidth requirements
- Sets: Matching physical and optical performance attributes
- Materials: Space-flight compatible
Narrow-band Filters
Our narrow-band filters are highly effective at isolating monochromatic emission and absorption lines, featuring high throughput, deep out-of-band attenuation, and close control of center wavelength. The performance of narrow-band filters is critically dependent upon AOI and operating temperature. Much care and attention is given to the design, manufacture, and measurement of these filters to assure that peak performance is reached at the designated system and operating environment.
Large Format Filters
As observational instruments and detectors increase in sensitivity and size, we continue to support the needs of the astronomy community through development of capabilities to produce filters with apertures as large as 210mm. Available scientific glasses can be combined to match existing requirements or to define novel filters. We continue to offer the highest finesse Fabry-Perot interference filters using both metal and dielectric reflectors.
Photometric Filters & Sets
We produce a variety of photometric filter sets (often called "UBVRI") that isolate broad areas of the spectrum. These filters are made by combining a number of filter glasses and/or dielectric spectral control films. They are useful for both color imaging and photometric classification. We produce many sets with modified designs to achieve required performance, such as accommodating the spectral response of detectors or maximizing peak energy.
Bessell Photometric Filter Sets
Our stock Bessell Photometric Sets, manufactured to the definition put forth by M. Bessell, offer high optical quality suitable for demanding imaging requirements. Filters are polished to stringent transmitted wavefront, wedge, and flatness specifications and are then anti-reflective coated. Each filter's spectral response is determined by the combined responses of Schott filter glasses polished to prescription thicknesses. The individual glasses are then laminated into a singlepiece optical assembly. The result is a set of precision filters at an economical price.
Specifications
| General Specifications: | |
| Curves: | Spectrophotometric curve(s) are provided for each filter or set. |
| Instructions: | Provided for handling & cleaning surface-coated optics. |
| Specifications for Filters U - I: | |
| Imaging Enhancement Attributes: | Maximum Transmitted Wavefront Distortion: 1/4 (or better) per inch. |
| Wedge: | < 30 arc seconds |
| Flatness: | 1/4 (or better) RMS per inch. |
| Surface Quality: | E/E as defined by Mil-C-48497A. |
| Anti-Reflective Coating: | Multi-layer dielectric AR coating on both surfaces. If required, R < 0.5% to increase transmission & reduce ghosting. |
| Anti-Reflective Coating Durability: | Moderate abrasion as defined by Mil-C-48497A (cheesecloth test). |
SDSS Photometric Filter Sets
The Sloan Digital Sky Survey (SDSS), which began in 1996, defined a photometric system to be used for the observation of secondary stars. The system is comprised of five color bands (u, g, r, i, z), which divide the spectrum from the UV (300nm) to the limits of CCD detection (1100nm) into five non-overlapping pass bands.
The SDSS system is the most popular photometric system currently in use. Its usefulness is a result of the fact that the Hubble Space Telescope is equipped with an SDSS set, which continues to provides the astronomical community with a large library of images that are used as a reference standard for additional observation. Omega has manufactured a wide variety of SDSS sets to the custom specifications required by individual observational instruments and experiments. All filters in a set are made to identical physical and imaging quality specifications.
The following prescription is taken from M. Fukugita et al's article "The Sloan Digital Sky Survey Photometric System," in the Astronomical Bulletin, Volume 111, Number 4, April 1996, and is representative of Omega's SDSS filter set specifications.
Please note, we make SDSS sets to custom specifications only.
Specifications
| General Specifications: | |
| Curves: | Spectrophotometric curve(s) are provided for each filter or set. |
| Instructions: | Provided for handling & cleaning surface-coated optics. |
| Specifications for Filters U - I: | |
| Imaging Enhancement Attributes: | Maximum Transmitted Wavefront Distortion: 1/4 (or better) per inch. |
| Wedge: | < 30 arc seconds |
| Flatness: | 1/4 (or better) per inch. |
| Surface Quality: | E/E as defined by Mil-C-48497A. |
| Anti-Reflective Coating: | Multi-layer dielectric AR coating on both surfaces. R typically < 0.5% to increase transmission & reduce ghosting. |
| Anti-Reflective Coating Durability: | Moderate abrasion as defined by Mil-C-48497A (cheesecloth test). |
Additional Information
Download our astronomy brochure (pdf, 3.5mb)