Note: Descriptions are shown in the official language in which they were submitted.
~ 34~9
SPECTROPHOTOMETER
The invention relates to a spectrophotometer with a dispersing
reflecting elemen~ and a multiple photodetector array arranged in
the evaluation plane.
For testing all sorts of samples, such as textile fibers and
fabrics, liquids and a variety of gases, particularly polluted air
etc., methods of spectral analysis are applied almost exclusively.
For this purpose, a series of spectrophotometers have been developed,
i.e., devices for measuring the spectral light intensity distribut;on
of a radiation. These methods permit a quick, safe and simple de-
termination of the composition of the samples that have been tested,
or the finding of specific components in these samples.
In a monochrometer described, for example, in the literature
reference "Classical Methods", Vol. 1, by I. Es~erman, Academic Press,
New York and London, 1959, pages 398 to 400, the images of the en-
trance gap generated in various colours are successively shifted over
an exit gap, or a radiation-sensitive element, respectively, by means
of a common movement of a dispersion prism and a plane mirror. Since
high resolution devices of that type require a very complex apparatus
the devices operating in accordance with this method are very expen-
sive, large and susceptible to disturbances. Because they are very
sensitive to shock and vibration, frequent and very time-consuming ad-
justments are unavoidable. As the intensities for the individual
spectral componen-ts are measured not simultaneously but successively
by rotating an optical arrangement sensitive to misadjustment, high
demands are made on the synchronism of the rotation with the times
of the individual measurings. Furthermore, any measurements carried
out with devices of the above described type are very time-consuming.
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1 It is the object of the invention to provide a spectrophotometer
which with an extremely simple structure, 1QW weight, and small dimen-
sions shows a high resolution, high sensitivity, and high working speed.
-- Furthermore, even relatively high deviations of the actual direction
from the nominal directions of the radiation to be analyzed are to be
without any influence on the measuring precision and the sensitivity.
The very high sensitivity of the spectrophotometer as disclosed by
the invention compared with s;milar devices in the prior art is achieved
particularly in that between entrance aperture and dispersing reflecting
1~ element a lens, preferably arranged in the immediate vicinity of the
: dispersing reflecting element, is provided which directs a beam from the
entrance aperture arranged near its focal plane, independently of its
angle of divergence, as a bundle of parallel beams onto the dispersing
reflecting element. Due to the small distance between lens and disper-
sing element, deviations of the direction of the central beam of the
diYergent bundle of beams passing through the entrance aperture, from
the optical axis oF the device, do not cause any important lateral
displacements and no changes of direction of the bundle of beams impinging
- on the dispersing reflecting element, so that there are no changes of
2~ position of the entrance aperture images associated to the individual
wavelength on the multiple photodetector array. As the lens which
- directs the bundle of beams to be analy~ed, independently of its angle
of divergence, provided that the angle is within the aperture angle of
the lens, and the direction of its central beam, onto the dispersing
reflecting element as a bundle of parallel beams, simultaneously provides
~he images of the entrance aperture which are associated with the in-
dividual wavelengths on the multi-photodetector array, the number of
optical elements required in the spectral photometer as disclnsed in the
i;nvention is sm~ller than in all formerly known comparable devices.
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1 Since a particularly small distance between the lens and the dis-
persing reflecting element is especially desirable in accordance
with the present invention, these two e1ements can be either cemented
to each other, or they can even be at a single body, so that the
simplicity and the robustness of the device as disclosed by the
invention with respect to vibration and shock or contamination are
considerably improved as compared with all known spectrophotometers.
As the plate with the entrance aperture can also be rigidly
connected to the multiple photodet:ec~or array, the spectrophotometer~
as disclosed by the invention, practically consists of two c~mponents
that are relatively easy to make in large-scale production, and are
connected to each other, without particularly high demands being
made to the mutual alignment~ by a sleeve or a length and width of a
few cm only.
The arrangement of the linear multiple photodetector array in
the immediate vicinity of the circular, square or rectangular en-
trance aperture largely avoids the oblique bundles and the errors
- connected therewith which in the known devices of this type are dif-
Ficult to prevent.
The inventior. will be described in detail below by means of the
figure representing an embodiment oF the invention. The embodiment
of the invention schematically represented in the Figure consists
of a sample holder l holding a sample 2 to be examined, a lens 20,
a plate 4 having a square aperture 3, a multiple photodiode array 5
arransed on that plate in the immediate vicinity of aperture 3 and
consisting of photodiodes 6, a lens 8 and a dispersing reflecting
element 9 designed as an echelon grating. Plate 4 is connected to
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1 dispersing element 9 by a sleeve 10 which at its top is closed by a
cover 21.
Sample 2 arranged on sample holder 1 is illuminated by an obliquely
impinging polychromatic radiation 11. Instead of oblique-angled il-
lumination it is also possible to provide a vertical illumination via a
semi-transparent mirror arranged between sample 2 and lens 20 (not shown
in the figure.) The radiation which is diffusely scattered or reflected
at a point of the surface of sample 2 is focused through lens 20 as a
convergent bundle of beams 12 within the entrance aperture 3 in the
focal point of lens 8, and exits therefrom as a divergent bundle of
; be~ms in the direction of lens 8. When passing through th;s lens the
divergent bundle of beams is transformed into a bundle of parallel
beams which at a small angle of incidence impinges onto dispersing
reflecting element 9. This is of such a design that the impinging light
is diffracted mainly in the direction of the first order of diffraction
only. As the direction of a diffraction order depends on the wavelength
the first diffraction order is reflected for each wavelength in another
direction and imaged through the lens on one respective photodiode 6
associated with a specific wavelength. To simplify the representation,
and to better understand these relationships, only one single beam 13
representing the right-hand limitation of the divergent bundle of beams
passing through entrance aperture 3 is shown. Beam 13 passing through
; lens 8 is transformed by that lens into a beam that is parallel to the
opti;cal axis of this lens~ and at the dispersion reflecting element 9 is
. .
diffracted only in the direction of the first order. The directions
~ssociated to the colours red, green, and blue are marked 13R, 13G and
:.
13B When passing through lens 8, these beams are deFlected in the
- direction of photodiodes 6R, 6G, 6G associated with their colours.
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1 It is quite obvious that the same process takes place with each
beam propagating in parallel to the optical axis of lens 8, and im-
pinging on the dispersing reflecting element 9 so that the radiation
of a specific wavelength reflected from the entire surface of the
dispersion element is respectively focused to one specific photodiode
5.
It is quite obYious that the measuring results with a bundle of
beams 12 having a sma11er angle of divergence, providing that bundle
of beams has the same light flux, are not different, and that the
measuring sensitivity is not reduced. If the beam passing through en-
trance aperture 3 shows an angle of divergence, as it will generally
be observed, which is much smaller than the aperture angle of lens 8
the djrectjon of the central axis of this beam is without influence
on the position of the images of the individual colour component on
multiple photodiode array 5 and on the measuring sensitivity. The
spectrophotometer as disclosed by the invention can therefore be used
in connection with a measuring microscope without any specific steps
for aligning the optical axis of the spectrophotometers to the optical
axis of the measuring microscope being required.
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