Optics: measuring and testing – By light interference – Spectroscopy
Reexamination Certificate
1999-01-06
2001-05-08
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
Spectroscopy
Reexamination Certificate
active
06229614
ABSTRACT:
TECHNICAL FIELD
The present invention concerns an interferometer for Fourier spectroscopy, in which the interferometer comprises a beamsplitter and two retroreflectors which substantially are arranged to form a Fourier transform spectrometer or interferometer.
The interferometer is particularly intended for measurements in the mid-infrared range and/or near-infrared range for determination of the quantities of specified (predetermined) components in a medium or fluid, specifically a liquid, such as a solution, e.g. an aqueous solution, and more specifically in a food product, e.g. a liquid food product such as milk. The interferometer is preferably constructed for use in the infrared range and especially in the mid infrared and/or near infrared range.
BACKGROUND ART
Typically used, known interferometers have two reflecting mirrors, in some interferometers in the form of retroreflectors. Generally one of the reflecting mirrors is mounted movably in a longitudinal direction, i.e. along the path of the radiation beam. The theory and use of interferometers are thoroughly described in “Fourier transform infrared spectrometry”, by Peter R. Griffiths and James A de Haseth, Vol. 83 in “Chemical Analysis”. In this specification the term “retroreflector” means an optical device, such as a comer reflector or cat eye, which will reflect an incident light ray in a direction which is parallel to the incident ray, as explained in the above-mentioned reference, e.g. FIG. 4.12 on p.144.
When constructing the arrangement for the movement or longitudinal displacement of the movable mirror, or reflector, great efforts have to be made to ensure controlled displacement. A reliable interferometer shall be substantially insensible to environmental vibrations. A good interferometer will primarily be sensible to vibrations in the same direction as the controlled movement of the movable part.
U.S. Pat. No. 4,383,762 discloses a two-beam interferometer for Fourier spectroscopy designed to be housed in a cryostat aboard a spacecraft, with rigid pendulum structure mounting at least one of the movable retroreflectors in a fully compensated optical system immune to tilt and lateral movement distortions. By this structure the linear displacement is replaced by a pivotal mounting of one or both retroreflectors. Similarly, EP 369 054 describes a pendulum reflector system for a Michelson interferometer. In FIG. 1 of EP 369 054 two retroreflectors are arranged on two perpendicular arms bearing on a common pivot. These interferometers are favourable in that sense that they can be made in such a way that they are only sensible to vibrations in the direction of rotation. Further the weight of the movable parts may be compensated by a balance weight. The driving mechanism must be dimensioned to suppress movements caused by environmental vibrations.
The purpose of the present invention is to provide a simple arrangement for an interferometer said arrangement being a structure which is cheaper to manufacture than the hereto known interferometers, and which simultaneously still has the properties necessary to obtain useful measurements, which are sufficiently accurate for the purpose of the actual measurement.
SUMMARY OF THE INVENTION
According to the invention the beamsplitter is arranged in a movable beamsplitter arrangement, e.g. mounted pivotally or rotatably, and both retroreflectors are fixed. Such mounting can be realised in a very simple way, by which a cheaper manufacturing of the interferometer can be obtained.
The new interferometer is specific advantageous in that it can be made substantially insensible to vibrations. This is due to the fact that the mass of the movable, rotatable or pivotable beamsplitter can be made small, i.e. it can be considerably smaller than the mass of retroreflectors. Therefore the moment of inertia of the rotatable beamsplitter arrangement can be small compared to the moment of inertia of the movable retroreflector arrangement of prior art Accordingly, by the new interferometer, it is easier to arrange a drive mechanism which will be able to suppress vibrations. Typically, vibrations tend to be a problem in interferometers, and especially in interferometers for milk analysis, due to the fact that such apparatus often includes a homogenizer and high pressure pumps generating vibrations.
As it will be explained in more details below, the movement of the beamsplitter creates a retardation and thereby a variable interference as in conventional interferometers.
Preferably, the beamsplitter is located in a plane which is at least nearly substantially coincident with a plane of symmetry of the two retroreflectors.
In a preferred embodiment the interferometer is specifically dedicated to the use for determination of the quantities of specified components in a medium or liquid, and more specifically in a liquid food product such as milk.
Further, the new interferometer has proved good spectral resolution in the mid-infrared range and even by short wavelengths i.e. in the near infrared range.
In the preferred embodiment of the new interferometer the structure is simple, simple to produce, and mechanically sturdy and stable.
REFERENCES:
patent: 4183669 (1980-01-01), Doyle
patent: 4320973 (1982-03-01), Furtunato et al.
patent: 4383762 (1983-05-01), Burkert
patent: 4915502 (1990-04-01), Brierley
patent: 5066990 (1991-11-01), Rippel
patent: 5196902 (1993-03-01), Solomon
patent: 5457529 (1995-10-01), Tank et al.
patent: 5764361 (1998-06-01), Kato et al.
patent: 369054A1 (1990-05-01), None
patent: 0369054 (1990-05-01), None
patent: 9524619 (1995-09-01), None
patent: 9611387 (1996-04-01), None
Peter R. Griffiths et al., “Fourier Transform Infrared Spectrometry,” Chemical Analysis, vol. 83, pp. 144-145.
Font Frank G.
Foss Electric A/S
Lee Andrew H.
LandOfFree
Interferometer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Interferometer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Interferometer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2488877