Optical: systems and elements – Having significant infrared or ultraviolet property – Having folded optical path
Patent
1994-04-05
1996-04-30
Lerner, Martin
Optical: systems and elements
Having significant infrared or ultraviolet property
Having folded optical path
359353, 359401, G02B 1314, G02B 2302
Patent
active
055130348
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an infrared optical system for handling two infrared (I.R.) beams of differing wavelengths through the same objective lens.
Imaging systems have been proposed in which a target is illuminated by a coherent I.R. source while being simultaneously viewed by an I.R. imaging system. Where it is desired to reduce the size of the apparatus incorporating such a system, both the coherent source and the imaging system might share some optical components, especially in the objective region. Furthermore, size limitations can create problems in the positioning of the coherent source and imaging system for optimum performance.
SUMMARY OF THE INVENTION
The present invention has arisen in an attempt to provide a compact optical system including a coherent I.R. source and an I.R. imaging system.
In accordance with the present invention there is provided an optical arrangement comprising, an I.R. imaging system operating at wavelengths less than 15 microns, a coherent I.R. source of shorter wavelength than said imaging system, a partially reflective member and an objective lens arrangement, the beams to the imaging system and from the source being directed to the partially reflective means which is disposed between the objective lens arrangement and the imaging system and source so as to cause the beams to pass through the objective lens along substantially the same optical path; and a T.V. camera which co-operates with an aperture formed in the side of the objective lens.
It is preferred that the partially reflective means is a beam splitter which transmits the imaging system wavelengths and reflects the coherent beam wavelengths along the optical path.
The objective lens is ideally capable of transmitting I.R. radiation in the range of 0.5 to 15 microns. The I.R. imaging system typically operates at a wavelength of 3-5 or 8-12 microns and the coherent source typically has a wavelength of around 1 micron.
The objective lens conveniently allows achromatic focusing at the imaging system wavelengths and transmission of the coherent source wavelengths.
The coherent source is typically a Nd:YAG laser.
It is preferred that the imaging system includes a zoom lens arrangement to assist in focusing, and an optical derotation arrangement to reduce the effect of movement of the apparatus. The optical derotation arrangement is conveniently a prism.
Preferably, the arrangement includes a controllable mirror after the objective lens arrangement.
The invention will now be described by way of example, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic partial side view of a device incorporating one embodiment of the invention;
FIGS. 2 and 3 show plan and side views, respectively, of the arrangements of optical components in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, the device shown therein comprises a pod for mounting externally on a vehicle such as an aircraft. The pod provides an infrared imaging system to the vehicle. In such cases, it is desirable to reduce the frontal area of the pod to a minimum to reduce air resistance. In the present case, the diameter of the pod is in the order of 300 mm. With such size restrictions, the positioning of components must be selected carefully in view of problems which can be encountered with excess optical path lengths and focusing restraints.
The apparatus shown comprises an I.R. imager 10, a Nd: YAG laser 20, an imager telescope 30, combining optics 40 and objective lens arrangement 50.
The I.R. imager 10 can be any proprietary system having suitable performance at wavelengths below 15 microns and suitable size, e.g. the class II thermal imaging common module scanner made by G.E.C. plc.
The Nd:YAG laser 20 is typically a low power source typically of 100 mJ operating at between 10 and 30 Hz, say 20 Hz with a 5 MW peak power.
The imager telescope 30, combining optics 40 and objective lens arrangement 50 are shown in more detail in FIGS. 2 and 3. Th
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Cameron Evan S.
Lessels Alison B.
Sillitto Hillary G.
Wilson Thomas B.
GEC Marconi Avionics (Holdings) Limited
Lerner Martin
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