Off-axis Design for Detector Applications

Compared with on-axis parabolic or ellipsoidal reflectors, the off axis mirrors do not have a central hole enabling light across the entire aperture of the mirror to be focused onto a detector. Moreover, by folding the optical axis and displacing the focus away from the mechanical axis, it is easier to install baffles to block stray light from paths outside the aperture from reaching the detector.

High Collection Efficiency

Off axis parabolic mirrors offer similar high numerical aperture to aspheric lenses without suffering from chromatic aberration when used over extremely wide wavelength ranges. The mirrors are ideal for collecting and concentrating light onto high speed detectors, or for collimating light output from broadband incoherent sources such as LEDs or super luminescent diodes.

Gold or Aluminum Reflective Coatings

Two metallic reflective coating options are available. Aluminum for UV and visible applications and bare Gold for infrared applications. The models listed are catalog versions of common OEM mirror designs.

Typical reflectance curves of metallic reflective coatings.

Integral Mount

Our off-axis replicated parabolic mirrors feature an integral mount at the base with the mounting hole pattern shown.

FTIR Spectroscopy Applications

In Fourier Transform Infrared (FTIR) spectroscopy, light from a broad spectrum point-like source is collimated and input into a split beam interferometer, such as a Michelson. Displacing one of the mirrors sinusoidally using a motorized mount creates a time dependent optical path difference (OPD) between the two interferometer arms. This OPD corresponds to a different number of wave cycles for each spectral component in the source. Spectral components that undergo constructive interference will output the system and be focused onto a detector. Spectral composition of the source may be calculated by taking the Fourier transform of the detected light intensity vs time. In FTIR, the maximum spectral resolution depends on system étendue, which is often limited by the size and collection angle of the detector. Off axis parabolic mirrors allow large collection angles without chromatic aberrations, which helps FTIR systems achieve high spectral resolution over wide spectral ranges.

Easily Accessible Focal Point

Compared with on-axis parabolic or ellipsoidal reflectors, and compared with lenses of similar light gathering capability, these off axis mirrors offer more convenient access to the focal point for placement of sources, detectors, and associated mounting hardware.