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Claims  |
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We claim:
1. Apparatus for measuring optical properties of a generally transparent
sample material, comprising:
a light source means for producing a substantially monochromatic beam of
collimated plane-polarized light along a first reference plane of
polarization at a selected wavelength;
a sample cell for containing the material to be measured, said sample cell
positioned in said beam and having transparent portions to allow passage
of said beam there through;
a first beam splitter positioned in said beam on a side of said cell
opposite the light source and operative to split said beam into first and
second test components;
first analyzer means positioned in the optical path of said first test
component and having a first polarizing axis oriented at an angle within a
first range of +5.degree. to +40.degree. with respect to a secondary
reference plane which secondary reference plane is oriented at an angle of
(+45.degree.) (n) with respect to said first reference plane wherein is an
integer, said first analyzer means for changing the intensity of said
first component as a function of the angle between said first polarizing
axis and said first reference plane of polarization;
second analyzer means positioned in the optical path of said second test
component and having a second polarizing axis oriented at a non-zero angle
with respect to said first polarizing axis and at an angle within a second
range of -5.degree. to -40.degree. with respect to a tertiary reference
plane which tertiary reference plane is oriented at angle of (
+45.degree.) (p) with respect to said first reference plane where p is an
integer, said second analyzer means for changing the intensity of said
second component as a function of the angle between said second polarizing
axis and said first reference plane of polarization;
first and second detector means receiving said first and second test
components after they have passed through said first and second analyzer
means, respectively, for producing first and second signals corresponding
to the intensities of said first and second test components, respectively;
and
processing means for comparing said first and second signals and for
producing an output corresponding to said optical properties.
2. Apparatus according to claim 1 wherein said first and second signals are
analog signals, said processing means including a linear amplifier
operatively to amplify said signals independently of one another and
analog to digital converter means for converting said analog signals into
corresponding digital signals.
3. Apparatus according to claim 2 wherein said first and second detector
means includes first and second photomultipliers.
4. Apparatus according to claim 1 wherein said light source means includes
a laser.
5. Appartus according to claim 1 wherein said light source means includes a
monochromatic light source, a first optical element to collimate light
from said light source and a second optical element to polarize said beam
along said first reference plane of polarization.
6. Apparatus according to claim 1 including a monochrometer means
associated with said light source and said sample cell for selectively
varying the wavelength of said monochromatic beam.
7. Apparatus according to claim 2 wherein said first and second detector
means includes first and second photocells oriented in the path of said
first and second test components, respectively.
8. Apparatus according to claim 1 wherein said first and second analyzer
means are first and second polarizing prisms, respectively.
9. Apparatus according to claim 8 wherein said first and second prisms are
Glan-laser prisms matched to the wavelength of light in said beam.
10. Apparatus according to claim 1 wherein said first beam splitter and
said first and second analyzer means are a Rochon prism.
11. Apparatus according to claim 1 including a second beam splitter
positioned in the optical path of said beam ahead of said first beam
splittter and operative to divide said beam into a secondary beam and a
third test component, said first beam splitter receiving said secondary
beam and operative to divide said secondary beam into said first and
second test components, and including third detector means receiving said
third test component for producing a third signal corresponding to the
intensity of said third test component, said processing means for
comparing said first, second, and third signals.
12. Apparatus according to claim 11 wherein the ratio of the intensity of
said secondary beam to the intensity of said third test component is
approximately 9:1.
13. Apparatus according to claim 11 including first, second and third fiber
optic means for transmitting said first, second and third test components,
respectively, to said first, second and third detector means,
respectively.
14. Apparatus according to claim 1 or 11 further including a third beam
splitter positioned in the path of said beam ahead of said sample cell and
operative to split a reference component beam from said beam, and a fourth
detector means receiving said reference component beam for producing a
fourth signal corresponding to the intensity of said reference component
beam, said processing means for comparing all said signals.
15. Apparatus according to claim 1 wherein said sample cell is a Faraday
cell.
16. Apparatus for measuring optical parameters of a generally transparent
sample material, comprising:
a sample cell adapted to hold the sample material to be tested;
a light source means for producing a substantially monochromatic beam of
collimated, plane-polarized light oriented at a primary reference plane of
polarization and for directing said beam through said sample cell;
beam splittting means on a side of said sample cell opposite said light
source means for splitting said beam into first, second and third light
test components;
first, second and third detector means for receiving, respectively, said
first, second and third test components and producing first, second and
third signals, respectively, in response to the intensity of the light of
its associated component;
a first analyzer element positioned in the path of one of said first,
second and third test components between said beam splitting means and an
associated detector means and a second analyzer element position in the
path of another one of said first, second and third components between
said beam splitting means and an associated detector means, said first
analyzer element having a first optical axis oriented at a positive angle
less than 45.degree. with respect to a secondary reference plane and said
second analyzer having a second optical axis oriented at a negative angle
greater than -45.degree. with respect to a tertiary reference plane where
said secondary reference plane is oriented at an angle of (45.degree.) (n)
with respect to said primary reference plane and said tertiary reference
plane is oriented at an angle of (45.degree.) (p) with respect to said
primary reference plane where n and p are integers and where the said
tertiary plane is at an angle with respect to said secondary plane that is
different from 45; and
processing means for comparing said first, second and third signals and
generating an output corresponding to said parameters.
17. Apparatus according to claim 16 wherein said first optical axis is
oriented at an angle within a range of +5.degree. to +40.degree. with
respect to said secondary reference plane and said second optical axis is
oriented at an angle within a range of -5.degree. to '40.degree. with
respect to said tertiary reference plane.
18. Apparatus according to claim 16 wherein said first optical axis is
oriented at an angle of approximately +30.degree. with respect to said
secondary plane and said second optical axis is oriented at an angle of
approximately -30.degree. with respect to said tertiary plane.
19. Apparatus according to claim 16 including first, second and third fiber
optic elements in the paths of said first, second and third components,
said fiber optic elements adapted to conduct each said component to its
respective detector means.
20. Apparatus according to claim 16 wherein said processing means includes
a linear amplifier operative to amplify said first, second and third
signals, an analog-to-digital converters to convert each of said amplified
signals into digital signals and a comparator means for comparing said
digital signals and outputting said parameters.
21. Apparatus according to claim 16 including a second beam splitting means
ahead of said sample cell for splitting a reference component from said
beam and a fourth detector for receiving said reference component and
producing a fourth signal, said processing means comparing all said
signals.
22. Apparatus according to claim 21 including a monochrometer means
associated with said light source for selectively varying the wavelength
of said beam.
23. A method for measuring the optical rotation properties of a relatively
transparent, optically active material comprising the steps of:
producing a primary beam of plane-polarized light oriented at a first
reference plane of polarization;
passing said primary beam through said material;
splitting said primary beam into a least first and second test components
after said beam has passed through said material;
passing said first test component through a first analyzing element having
a first polarizing axis oriented at an angle within a first range of
+5.degree. to +40.degree. with respect to a secondary reference plane
which secondary reference plane is oriented at an angle of
(.+-.45.degree.) (n) with respect to said first reference plane where n is
an integer;
passing said second test component through a second test component through
a second analyzing element having a second component through a second
analyzing element having a second polarizing axis oriented at a non-zero
angle with respect to said first polarizing axis and at an agnel within a
second range of -5.degree. to -40.degree. with respect to a tertiary
reference plane which tertiary reference plane is oriented at an angle of
(.+-.45.degree.) (p) with respect to said first reference plane where p is
an integer;
producing first and second analog signals corresponding to the intensity of
said first and second test components after each has passed through its
respective analyzing element;
amplifying said first and second analog signals;
converting said first and second analog signals into first and second
digital signals after they have been amplified; and
comparing said first and second digital signals to generate an output
indicative of the optical rotation of said material.
24. The method according to claim 23 including the steps of splitting a
reference component said primary beam prior to passing said primary beam
through said sample and producing a third analog signal corresponding to
the intensity of said reference component, converting said signal into a
third digital signal and comparing said third digital signal with said
first and second digital signals.
25. The method according to claim 24 including the step of varying the
wavelength of said primary beam.
26. The method of measuring the parameters of absorption, depolarization
and rotation of a beam of light in an optically active material comprising
the steps of:
producing a collimated primary beam of plane-polarized light;
passing said primary beam through a sample of said material;
splitting said primary beam into first, second and third test components
after said beam has passed through said material;
passing each of said second and third test components through a polarizing
element;
producing a first signal corresponding to the intensity of said first test
component and second and third signals corresponding to said second and
third test components after each of said second and third test components
has passed through its respective polarizing element; and
comparing said first, second and third signals to determine said
parameters.
27. Claim 26 further including the step of subjecting said sample material
and said beam while in said sample material to a controlled
electromagnetic field.
28. The method according to claim 26 including the steps of splitting a
reference component from said primary beam prior to passing said primary
beam through said sample and producing a fourth signal corresponding to
the intensity of said reference component and comparing all said signals.
29. The method according to claim 28 including the step of varying the
wavelength of said primary beam. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring
various optical properties of materials, including the properties of
absorption, optical rotation and depolarization. While the present
invention has been constructed to be used as a detector for
chromatographic separations, the device may be employed in situations
where measurement of these optical properties is desired for a generally
transparent, fluid material.
Various polarimeters have been developed in the past, and many of these
have been based on a common physical principle that, when plane-polarized
light is passed through a material, the plane of polarization of the light
is rotated. As is known, nonpolarized light has random orientations, that
is, it is composed of light comprised of tranverse waves having all
orientations around the axis of propagation, while plane-polarized light
is composed of transverse waves having a single orientation with respect
to this axis of propagation. Certain substances have the ability to rotate
plane-polarized light as it passes through the substance. That is, these
substances rotate the orientation of the polarized light about the axis of
propagation as the light passes through the substance. The amount of this
rotation is related to the substance or material rotating the light, the
concentration of the substance, and the path length of light through the
substance. Specifically, the specific rotation of the substance is:
##EQU1##
where:
##EQU2##
Implied in this equation is that specific rotation is dependent upon the
temperature of the substance and the wave length of the light used to
measure the rotation. By convention, counterclockwise rotation about the
axis of propagation is given a negative sign, and clockwise rotation is
given a positive sign. Standard measurements are normally conducted at
25.degree. C. with the sodium d line of 5891 angstroms in order to
eliminate the variables of temperature and wavelength.
In most prior art devices, optical rotation is observed by passing the
rotated light through an analyzer in the form of a polarizing filter, such
as a prism whose optical axis is oriented at an angle with respect to the
original plane of polarization. The intensity of the light is diminished
by an amount dependent upon the angle of the plane of polarization after
rotation and the optic axis of the analyzer. In many prior art devices,
the analyzer is oriented in a crossed configuration, i.e. 90.degree., from
the orientation of the plane-polarized lights in order to minimize the
amount of light which would pass through the analyzer and reach a detector
and therefore the intensity of light at the detector. A sample cell
containing the material to be tested is placed between the polarizer and
the analyzer so that any rotation of the polarized light as a result of
the material will be evidenced by an increase in the intensity of light
reaching the detector. Typically, these devices measure the optical
rotation by mechanically rotating either the analyzer or the polarizer so
that the intensity of light at the detector is reduced to a minimum value
or null position. The amount of rotation of the polarizer or analyzer is
then exactly equal to the rotation property [.alpha.] of the sample.
An alternative to mechanical rotation found in the prior art is the
rotation twisting of the light by the use of a Faraday rotator. A Faraday
rotator is simply a material (optically active or not) that is immersed in
a magnetic field along the axis of the transmitted light. The light beam's
plane of polarization is rotated proportionally to the strength of the
magnetic field component of the Faraday rotator and the length of the
light path therethrough.
Examples of these various prior art devices may be found in U.S. Pat. No.
3,510,226 issued May 5, 1970 to Kerry which shows a Faraday coil being
used as a compensator for rotation caused by a sample to be measured. U.S.
No. Pat. No. 3,361,027 issued Jan. 2, 1968 to Kaye teaches rotation of the
polarizer to compensate for the angle of rotation of the sample material
while U.S. Pat. No. 4,306,809 issued Dec. 22, 1981 to Azzam teached the
use of measuring the rotation of light by means of quarter wave plates.
It is also possible, however, to measure the rotation of the polarized
light through the medium by monitoring the intensity of the light at the
detector and utilizing this intensity as a basis for calculating the
amount of optical rotation. In T. Crumpler et al, "Simple Photoelectric
Polarimeter", 27 Analytical Chemistry #10 (1955), the polarizer and
analyzer filters are oriented at a fixed angle of 45.degree. with respect
to one another. This angle provides for the maximum change in intensity at
the detector per unit rotation of the light. Inherent limitations of this
system were improved upon in various devices wherein a polarized beam was
split, either before or after it is passed through a sample cell, and then
is subjected to two analyzer polarizing filters oriented at +45.degree.
and -45.degree. with respect to the orientation of the first polarizing
element. Thus, any optical rotation caused by the sample material would
cause an increase in intensity passing through one analyzer while a
decrease in intensity in the other analyzer.
Despite these improvements in polarimeters, there still remained a need to
provide a method and apparatus for overcoming inherent design limitations
of these prior art devices. More particularly, the need remained for an
optical measuring device which was able to measure various optical
properties of a substance, including the optical rotation, the
depolarization, and absorption characteristics of a sample material.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel
and useful method and apparatus for measuring various optical parameters
of a material.
Another object of the present invention is to provide a method for
simultaneously measuring the optical rotation, the depolarization, and the
absorption of light passing through a sample of material.
A still further object of the present invention is to provide a method and
apparatus for producing signals indicative of optical characteristics of a
sample material which signals can be digitalized and enhanced to provide
highly accurate information regarding various optical parameters of a
sample material.
It is yet another object of the present invention to provide a method and
apparatus for measuring various optical parameters of a material in such a
manner that the sensitivity of the device can be selectively increased
over a diminished range of operation.
To accomplish these objects, the method according to the preferred
embodiment of the present invention comprises the steps of producing a
beam of plane-polarized light which is then passed through the material
whose parameters are sought to be tested. A reference component of this
beam may, if desired, be split from the beam before passing the main beam
through the material to be tested in order to allow the monitoring of the
fluctuation of source light intensity. After passing the main beam of
light through the sample material, the beam is split into first and second
test components, and then each of these test components is passed through
an analyzer in the form of a polarizing element. Each of the analyzers
have an optical plane which is oriented at a pre-selected angle with
respect to the plane of the initial plane-polarized beam and at a
pre-selected angle with respect to one another. By comparing the intensity
of the light which passes through each analyzer, measurement of the
optical rotation caused by the material is possible since the intensity of
the component beams are affected in proportion to the amount of optical
rotation. These intensities are detected and are used to generate a pair
of analog signals which are then amplified and coverted into digital
signals. After the digital signals are generated, the signals are compared
to allow mathematical calculation of the optical rotation and removal of
measurement errors.
Preferably, the preferred method includes a simultaneous measurement of
absorption, depolarization, and rotation of the beam of light passing
through the sample material, since the absorption and depolarization
properties of the material may affect the intensity of the derivative
component beams and thus affect the optical rotation reading. To
accomplish the simultaneous measurement of these parameters, the beam is
preferably split into three components after it is passed through the
sample material, and two of these components are then passed through
analyzer elements in the form of polarizers oriented as described above,
but which have optical polarizing axes oriented at an angle different than
0.degree. or 90.degree. with respect to one another. The intensity of
third component is monitored directly to provide absorption and
depolarization data, with the intensity of all three components being
measured by a suitable detector means. The intensities of the three
components may then be used to calculate the three parameters desired. One
or more half wave plates may be placed in the path of the beam after it is
passed through the sample cell and before it is split to increase the
sensitivity of this method while at the same time decreasing its effective
range of measurement.
To implement the above-described method, a polarimeter apparatus is
provided which includes a light source that emits a monochromatic beam of
collimated, plane-polarized light. This light source can be a laser or a
more conventional monochromatic source that emits a beam that is passed
through a polarizing filter and collimating elements. A beam splitter may
be used to split a reference component from the main beam. A sample cell
is provided to hold the material to be measured, and the main beam from
the light source is directed through the sample cell. One or more beam
splitters intercept the beam of light after it has passed through the
sample cell to split this beam into two or three components. At least two
of these components are test components and are passed through analyzers
in the form of polarizing elements which have their optical axis oriented
at a pre-selected angles with respect to the plane of polarization of the
original light beam and at a pre-selected angle with respect to one
another. Photodetectors then measure the intensity of the various
components and produce analog signals which are then individually
amplified by a linear amplifier. The amplified signals from the linear
amplifier are passed to an analog-to-digital converter which converts all
of the analog signals into digital signals. These signals are then
compared by appropriate data processor means to generate a display of the
characteristics to be measured. Further, optical fiber elements may be
provided to conduct the light beam or the beam components during the
measurement process.
These and other objects will become more readily appreciated and understood
from a consideration of the following detailed description of the
preferred embodiment when taken together with the accompanying drawings,
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagramatic representation of the components forming the
apparatus for and implementing the method of measuring the optical
rotation of a sample material according to the embodiment of the present
invention; and
FIG. 2 is a diagramatic representation of the components forming the
apparatus for and implementing the method of simultaneously measuring the
optical parameters of rotation, depolarization, and absorption according
to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention directed to a novel method and optical apparatus for
measuring various optical properties of a sample material. Of primary
importance to this method and apparatus is its ability to measure the
rotation of plane-polarized light passing through the sample material. In
addition, since the parameters of absorption and depolarization of the
material are desirable parameters to measure, the method and apparatus
according to the present invention accomplishes these measurements as
well.
As is well known, when plane-polarized light is passed through certain
optically active materials, these materials rotate the plane of the
polarized light from a few hundredths of a degree to several hundred or
even several thousand degrees. The measurement of the specific rotation
which a material imparts to a plane-polarized beam of light is a common
physical property reported in the literature. The present invention, in
addition to measuring this optical rotation, is also directed to measuring
the absorption properties of the material to be tested as well as the
depolarization effect the material has on a beam of polarized light.
Accordingly, the present invention is particularly useful as a polarimeter
adapted for chromatographic apparatus.
Referring now to FIG. 1, there is shown a diagramatic representation of the
apparatus according to the preferred embodiment of the present invention
which is designed to measure the specific rotation of a beam of
plane-polarized light passing through a sample material. In this diagram,
a light source 10 is provided which has suitable optics for producing a
beam 12 of collimated monochromatic light. Beam 12 is directed through a
polarizer element 14 so that it emerges as a collimated beam 13 of
monochromatic, plane-polarized light having of polarization that may be
referred to as the 0.degree. or reference plane. Beam 13 is then directed
through a beam splitter 15 so that it is split into a main beam 17 and a
reference component 19. Main beam 17 is then directed a sample cell 16
which contains the material to be studied, and it should be appreciated
that sample cell 16 is designed to contain a normally optically active
substance. To this end, sample chamber 16 has a relatively transparent
cross-section in the direction of beam 17 so that a minimal attenuation of
beam 17 occurs as it passes through the cell 16. Thus, any attenuation is
a result of interaction between the beam and the material contained in
ce11 16. Sample cell 16 is a standard flow through cell having an inlet 21
and an outlet 23 so that fluid material may be pumped through cell 16.
Beam 17 is then directed to a beam splitter element 18 which splits beam 13
into a first test component 20 and a second component 22. Component 20 is
then passed through a first analyzer element 26 and is then received by a
first detector 28. Similarly, component 22 is passed through a second
analyzer element 36 and is then received by a second detector 38.
Reference component 19 is directed by a mirror 25 to a third detector 32.
Suitable optics are provided to direct light beams 12, 13, 17, and
components 19, 20 and 22, as exemplified by mirrors 24 and 25. These path
elements, such as mirrors 24 and 25, are passive elements whose kind,
number and position are determined by the physical dimensions of the
device and the relative orientation of the active components, and can be
conveniently selected by one ordinarily skilled in the art without the
need for experimentation.
Detectors 28, 32 and 38 are preferably photodetector cells which produce an
electric signal in response to the intensity of light which each receives.
These electric signals are respectively transmitted by way of electrical
leads 30, 34 and 40 to a linear amplifier 50 which individually amplifies
the electric signals and passes the signals by means of electrical
connections 52, 53 and 54 to an analog-to-digital converter 60. The analog
information generated by detectors 28, 32 and 38, and amplified by linear
amplifier 50, is then converted into digital information by
analog-to-digital converter 60. This data then is presented, by means of
electrical leads 62, 63 and 64 to comparator processor 70 which processes
the digital information to generate a display on display 80 which
corresponds to the optical rotation and absorption of beam 17 caused by
the sample material in cell 16. It should be understood that this
processing may be implemented by processing software according to
generally understood principles, and the comparison of the relative
intensities of components 20 and 22 allow calculation of the optical
rotation caused by the sample material in cell 16. Measurement of
reference component 19 permits the user to correct the measurement of
absorption and optical rotation by permitting the factoring out of
intensity fluctuations occurring at source 10.
From the foregoing, the broad method according to the preferred embodiment
of the present invention includes the first step of producing a collimated
beam of plane-polarized light and then passing this beam through a sample
of material to be measured. This beam is then split into at least first
and second test components, such as components 20 and 22, after the beam
has passed through the material with each of these first and second
components then being passed through an analyzer element in the form of
analyzer prisms 26 and 36 shown in FIG. 1 oriented at a pre-selected angle
with respect to one another. First and second analog signals are then
produced in response to the intensity of light in the first and second
components 20 and 22. These first and second analog signals are then each
amplified and then converted into first and second digital signals. These
first and second digital signals are finally compared to generate an
output indicative of the optical rotation of the material. An improvement
of this broad method is found in the step of splitting a reference
component from the beam prior to passing the beam through the sample cell
and then producing a third analog signal in response to the intensity of
the reference component, amplifying this third analog signal and
converting it into a third digital signal for comparison with the first
and second digital signals.
As was shown in FIG. 1, light source 10 and polarizer element 14 provide a
beam 13 of plane-polarized, collimated light. A number of different light
sources can be employed to generate the collimated, monochromatic
plane-polarized beams, but it is preferred that light source 10 be a
laser, such as a low pressure helium-neon laser that produces polarized
light. If such a laser is used, polarizer element 14 can be eliminated
since the beam 12 would already be collimated and plane-polarized as it is
emitted from light source 10.
Alternative sources of light may be used as light source 10, for example,
an incandescent light may be used if proper filters are provided to filter
the incandescent source into a monochromatic beam, and collimating lenses
are provided to collimate the light from the incandescent source. In this
case, a polarizing element 14, preferably in the form of a Glan-laser
prism should be used to polarize the beam as described above. If the
requirements of the system are such that a low intensity light beam is
acceptable, a light-emitting diode may be used for a light source, and
indeed, various laser diodes, which are presently in the development
stage, may prove suitable for use in this apparatus and method.
After the beam of plane-polarized light is produced in the first method
step, the main beam is passed through the material to be tested with this
material being contained in sample cell 16. Sample 16 is a standard
flow-through cell that is used in existing polarimeters or for purposes of
chromatography and is generally transparent to the wavelength of light
comprising beams 13 and 17. After passing beam 17 through the material to
be tested, the beam is split into the first and second test components 20
and 22 by a standard beam splitter 18. Although it is preferred that beam
splitter 18 produce components 20 and 22 having equal intensities, such a
splitting of beam 17 is not an essential requirement since unequal
proportion can be compensated for in the data processing operation. It is
a requirement of the system, then, that the split ratio of beam splitter
18 be known so that this ratio can be compensated by the software of the
comparator processor to generate accurate information. Preferably, beam
splitter 18 is a dielectric beam splitter havinq as nearly a ratio of
one-to-one as possible.
After beam 17 is split, first and second test component beams 20 and 22 are
each passed through polarizing elements or analyzers 26 and 36. It should
be appreciated that these analyzers could also take many different forms.
In the preferred embodiment, analyzers 26 and 36 are Glan-laser prisms,
but other calcite prisms such as Glan-Thompson, Nicol or Wollaston prisms
could replace the Glan-laser prisms of the preferred embodiment, but in
such case, care must be taken that the prisms are matched to the
wavelength of components 20 and 22. Indeed, stacks of plate polarizers or
polaroid filters could be used to interact with the polarized light in
components 20 and 22. Further, a single Rochon prism having its optical
axis oriented at 45.degree. with respect to the reference plane of
polarization could replace beam splitter 18 and both analyzers 26 and 36,
since it is well known that a Rochon prism both splits the incident beam
and interacts as a polarizing element with each component of the polarized
light.
After the step of passing the component beams through the analyzers is
completed, the preferred method, as set forth above, measures the
intensity of the light in each component. It should be appreciated that
these intensities may be varied by the analyzers. The reason for this is
that the intensity is proportional to the angle between the plane of the
plane-polarized light after it has passed through the sample material and
the polarizing axis of each analyzer. Since the analyzers have polarizing
axes oriented at an angle with respect to one another, the intensity of
each component is varied differently by each analyzer, depending upon the
angle of the polarizing axis of the incident light. To this end, the
polarizing axis of each analyzer 26 and 36 is oriented at a pre-selected
angle with respect to the plane of beam 13 and at a pre-selected angle
with respect to each other. The interrelationships of these angles are
discussed in greater detail below.
A second form of the present invention is shown in diagramatic
representation in FIG. 2 and is a more sophisticated system for
simultaneously measuring the optical rotation, depolarization and
absorption of light resulting from interaction with the sample material.
Here, a light source 110 is provided which produces a collimated beam 111
of light. Beam 111 is directed through a monochrometer 112, which may
optionally be used in this system but is not required, and then through a
polarizing element 114 to produce a plane-polarized beam 113 of collimated
light having a wavelength governed by monochrometer 112. Should
monochrometer 112 be eliminated, it is necessary that optical elements be
employed to ensure that beam 113 is monochromatic. In the alternative, a
laser source could be used, as discussed above.
Beam 113 is then directed by mirror 109 to a beam splitter 115 which splits
beam 113 into a main beam 117 and a reference beam 119. Main beam 117 is
directed through a sample cell 116. Sample cell 116 includes a Faraday
coil 123 which extends around sample ce11 116 as is known in the art so
that the energizing of coil 123 to selected levels causes a normally
non-optically active material in cell 116 to become optically active.
Sample cell 116 has an inlet 125 and an outlet 127 which permits fluid
sample material to be pumped through cell 116.
After beam 117 has passed through cell 116, it is directed toward a beam
splitter 118. Upon reaching first beam splitter 118, beam 117 is divided
into a first test component 120 and second | | |
