Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1983-05-24
1987-06-30
Rosenberger, R. A.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
250353, 350619, 356246, G01N 2101, G02B 512, G02B 1706
Patent
active
046766529
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the optical instrument making industry and, more specifically, to multiple pass optical systems.
BACKGROUND OF THE INVENTION
At present multiple pass optical systems featuring a long optical path length are an integral part of every IR spectrophotometer for examination of low-concentration gases or those having very faint absorption bands. Such systems are applicable both for qualitative and quantitative analyses.
One prior-art multiple pass optical system is known (cf. Journal of the Optical Society of America, 1940, v. 30, 338-342, H. D. Smith, L. R. Marshall), wherein the radiant flux emitted by the illuminator passes through the entrance aperture of the casing onto a mirror objective rotatably mounted across the path of the radiant flux, and further onto the unit of intermediate images of the illuminator radiation source, from which the radiant flux is directed again onto the reflecting objective and, on being reflected from said objective, the radiant flux completes the multiple pass cycle and emerges from the system through the exit aperture of the casing. In the above described optical system, the unit of intermediate images of the illuminator radiation source comprises two plane mirrors arranged at an angle to each other.
However, when focusing the intermediate images of the illuminator radiation source in the aforesaid system, the marginal beams fail to get restricted on the flat mirror surfaces, whereby when reflections of the beam are multiply repeated a considerable proportion of the emitted radiant flux is scattered beyond the faces of the reflecting objective (that is, vignetting of the slanted beams occurs).
SUMMARY OF THE INVENTION
The present invention is aimed at the provision of a multiple pass optical system, wherein the unit of the intermediate images of the illuminator radiation source would be so embodied as to increase the luminous transmittance of the system and to simplify the adjustment of the number of passes of the radiant flux.
This is accomplished in a multiple pass optical system, when the radiant flux emitted by the illuminator passes through the entrance aperture of the casing and is incident upon a reflecting objective mounted pivotally about its axis in a path of the radiant flux. The flux is reflected onto the unit of the intermediate images of the illuminator radiation source, from which the radiant flux is directed again onto the mirror objective to be reflected therefrom to complete the multiple-pass cycle by emerging from the system through the exit aperture of the casing thereof, according to the invention, the unit of the intermediate images of the illuminator radiation source is fashioned as a compound collective, comprising two different-curvature mirrors so positioned that the angles of incidence of the radiant flux upon the larger-curvature mirror are less than the angles at which said flux is incident upon the smaller-curvature mirror.
It is expedient that one of the mirrors of the compound collective be planar and the other be concave.
Sometimes it is desirable that both of the mirrors of the compound collective be concave.
It is possible, in order to modify the mode of operation of the multiple pass optical system of the invention, that a holder-carried specimen be placed across the pathway of the radiant flux for the specular reflectance of its plane surface to measure, the mirror objective being so turned round its axis along an arc at the instant the measurement is taken that the radiant flux is alternately incident upon the reflecting objective and the compound collective and upon terminating the final pass of the cycle, the radiation flux is brought directly to the exit aperture.
It is likewise reasonable that the mirror objective be turned round its axis along an arc by means of a pivotally mounted lever arranged coaxially with the specimen holder and carrying the reflecting objective at one of its ends.
The present invention makes it possible to avoid vignetting of the slanted beams in th
REFERENCES:
patent: 3687519 (1972-08-01), Mapes
patent: 3726598 (1973-04-01), Gilby
patent: 3963328 (1976-06-01), Abel
patent: 4209232 (1980-06-01), Chernin
patent: 4210401 (1980-07-01), Batten
Smith et al., "Method for Obtaining Long Optical Paths", J.O.S.A., Aug., 1940, vol. 30, pp. 338-342.
Barskaya Evgenia G.
Chernin Semen M.
Semenova Galina P.
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