FILTERS FOR ASTRONOMY & AEROSPACE

Bringing Information to Light

Filters for Astronomy and Aerospace Introduction

O

MEGA

O PTICAL designs and

a wide variety of bandwidths with highly controlled cut-on and cut-off edge slope.

manufactures custom filters

Available scientific glasses can be com-

and standard prescription filters

bined to match existing requirements or to

to the highest imaging quality standards

define novel filters. We continue to offer

for astronomers, atmospheric scientists,

the highest finesse Fabry-Perot interference

and aerospace instrumentation companies

filters using both metal and dielectric

worldwide. Applications include both

reflectors.

terrestrial and space-based observational

Glowing in the constellation Aquila like a giant eye, the plane-

instruments. We have supplied projects and

Custom Filters

programs for a wide variety of prestigious

Many astronomy imaging applications

universities, observatories, government

require the custom design and manufacture

agencies, and international consortia. As

of filters and filter sets. With more than

tary nebula NGC 6751 is a cloud

instrument technologies and applications

twenty vacuum deposition systems—includ-

of gas ejected several thousand

evolve, we work collaboratively with

ing IAD, electron beam, plasma enhanced,

years ago from the hot star visible

customers to develop solutions for the

and multi-planet coating technologies—we

spectral, optical, and environmental

are able to produce filters of extreme uni-

demands that will define observational

formity and precision in quantities of one to

astronomy and aerospace applications

one thousand according to the following

in the future.

general specifications:

in its center. Images are taken through different filters, including Omega filter F555W, in order to isolate nebular gases of different

■

Wavelength Range: UV to mid IR

temperatures. The images are

Large Format Filters

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Bandwidths: 0.15nm to several hundred nm

then digitally combined and

As observational instruments and detectors

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Tolerances: Critical throughput, band-

pseudo-colored. Image courtesy

tinue to support the needs of the astronof NASA’s Jet Propulsion Laboratory.

shape and bandwidth requirements

increase in sensitivity and size, we con■

performance attributes

omy community through development of capabilities to produce filters with apertures as large as 210mm. These filters are well matched for manufacture using Omega’s proprietary ALPHA™ Technology, producing

Sets: Matching physical and optical

■

Materials: Space-flight compatible

Capabilities and Features

temperature, and imaging quality. Continuum filter sets are made with precise

High Spectral Performance

matching of the cut-on and cut-off wave-

We provide interference passband filters

lengths of spectrally adjacent filters. Space-

with peak wavelengths located from the UV

based application filters are manufactured

to the mid-IR and with bandwidths ranging

using “space-flight compatible” materials.

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.

Photometric Filter 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

Previously unseen details of a

required performance, such as accommoHigh Optical Performance Our filters are made to rigorous imaging

dating the spectral response of detectors or maximizing peak energy.

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. Our Broadband Achromatic Twyman-Green interferometer enables us to evaluate transmitted wavefront at the filter’s principal wavelength. Durable anti-reflective coatings are deposited on outer surfaces to increase transmission and reduce ghosting. Physical Attributes Many 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

mysterious, complex structure within the Carina Nebula, one of the outstanding features of the

Narrow-Band Filters

Southern-Hemisphere portion of the

Our narrow-band filters are highly effective

Milky Way, as revealed by NASA’s

at isolating monochromatic emission and

Hubble Space Telescope image of

absorption lines, featuring high throughput, deep out-of-band attenuation, and close

the “Keyhole Nebula.” The picture

control of spectral location. The perform-

is a montage assembled from four

ance of narrow-band filters is critically

telescope pointings with Hubble’s

dependent upon system speed and operat-

Wide Field Planetary Camera 2,

ing temperature. Much care and attention is

using six color filters, including

given to the design, manufacture, and measurement of these filters to assure that

Omega Optical’s F439W, F555W,

peak performance is reached at the desig-

and F814W. Image courtesy of

nated system and operating environment.

NASA’s Jet Propulsion Laboratory.

Bessell Sets

N 49 is a supernova remnant within the Large Magellanic Cloud, a nearby, small companion

O

UR STOCK

Bessell Photometric

anti-reflective coated. Each filter’s spectral

Sets, manufactured to the defini-

response is determined by the combined

tion put forth by M. Bessell, offer

responses of Schott filter glasses polished

high optical quality suitable for demanding

to prescription thicknesses. The individual

imaging requirements. Filters are polished

glasses are then laminated into a single-

to stringent transmitted wavefront, wedge,

piece optical assembly. The result is a set

and flatness specifications and are then

of precision filters at an economical price.

galaxy to the Milky Way, visible 100

from the Southern Hemisphere. The Hubble Heritage image of

90

N 49 is a color representation of

80

data taken with Hubble’s Wide

filters F814W (I) and F547M were used to sample light emitted by sulfur ([S II]), oxygen ([O III]), and

% Transmission

Field Planetary Camera 2. Omega

70 60 I

R 50 U

V

B

40

hydrogen (H-alpha). Image

30

courtesy of NASA’s Jet

20

Propulsion Laboratory.

10 0 300

400

500

600

700

800

900

1000

1100

Wavelength (nm) Figure 1: Bessell Photometric Set Spectral curves of Bessel U, B, V, R, I filters.

Imaging Enhancement Attributes ■ Transmitted Wavefront Distortion: λ/4 (or better) per inch.

■ Anti-Reflective Coating: multi-layer dielectric AR coating

■ Wedge: Less than 30 arc seconds.

on both surfaces. R typically