Illumination – Light source and modifier – Including reflector
Patent
1995-01-25
1998-06-30
Quach, Y.
Illumination
Light source and modifier
Including reflector
362299, 362304, 362346, F21V 900
Patent
active
057723133
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to an optical system operable to focus an annular beam of light onto a spot.
In reflection densitometry there is often a requirement to illuminate a sample at 45.degree. with light of a narrow beam width, see International Standards Organization ISO Standard 5/4 `Geometric conditions for reflection density`. This ideally takes place over a full 360.degree. cone to ensure that the orientation of directionally reflective materials does not effect the resulting measurement.
If an optical system for forming a narrow annular beam converging at 45.degree. onto a spot on a sample to illuminate that spot is formed substantially as is described in GB-A-2191572 or, alternatively, comprises a lamp mounted at the centre of the reflective surface of a paraboloidal reflector so as to produce a substantially parallel beam of light, a disc mounted co-axially with the axis of the paraboloidal reflector in the path of the parallel beam of light so as to restrict that beam such that the light that passes it is an annular, parallel beam of light co-axial with the axis of the reflector, and a simple converging lens mounted co-axially with the axis of the paraboloidal reflector on the other side of the disc remote from the paraboloidal reflector whereby the annular parallel beam is caused to converge and focus on the spot which is on the axis of the paraboloidal reflector, the required lens must have a large focal ratio (f
o). This is difficult to achieve and, in addition, there is little space available between the lens and the sample to house the necessary detector which senses light reflected by the sample perpendicular to its plane.
An object of this invention is to provide an optical system which more easily achieves the desired result than is the case when a simple converging lens is used and which provides adequate space for accommodation of a detector operable to sense the light reflected perpendicular to the sample plane.
U.S. Pat. No. 4,422,135 discloses the use of an aspherical mirror arranged so that its reflecting surface has an annular concave form extending around an axis of rotational symmetry, the radial cross-section being that of an elliptical segment. A cylindrical mirror is connected to the radially outer edge of the aspherical mirror and focuses the convergent annular beam to form a single spot image on the axis of the annular beam. Although this arrangement eliminates the need for a lens having a large f
o it does not increase the space available to house the detector.
According to this invention there is provided an optical system operable to focus an annular beam of light onto a spot, the system comprising a light source, optical means operable to form light emitted by the light source into an annular beam having a convergent annular width the optical means comprising a concave mirror having an axis of rotational symmetry which is coincident with the axis of the optical system and an annular mirror interposed co-axially in the path of the annular beam and positioned so as to be impinged by the latter before it has focussed to form a narrow annular image, the annular mirror being operable to deflect the annular beam whereby to form a single spot image on the axis of the annular beam, wherein the annular mirror comprises a conical mirror and the optical means are arranged so that said annular beam converges towards said conical mirror symmetrically with respect to each line parallel to the optical axis and located on a notional right cylindrical surface which has said narrow annular image as its diameter and which is coaxial with the axis of the optical system.
In one embodiment, said optical means comprise means operable to form light emitted by the light source into an annular parallel beam of light and an annular converging lens mounted co-axially with and in the path of the annular parallel beam and operable to converge it into said annular beam having a convergent annular width.
Preferably said means operable to form light emitted by the light source into an annu
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patent: 3825322 (1974-07-01), Mast
patent: 4389701 (1983-06-01), Phillips
patent: 4422135 (1983-12-01), McCamy
Applied Optics, vol. 7, No. 10, 15 May 1978, pp. 1532-1536, Rioux et al, "Linear, Annular, and Radial Focusing with Axicons and Applications to Laser Machining."
Japanese abstract, "Irradiating Method for Laser;" vol. 7, No. 25, (M-190) (1170) 02 Feb. 1983.
Bailey, Sr. Clyde E.
Eastman Kodak Company
Quach Y.
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