U.S. patent number 3,783,276 [Application Number 05/259,868] was granted by the patent office on 1974-01-01 for dual beam optical system.
This patent grant is currently assigned to Instrumentation Specialties Company. Invention is credited to Robert W. Allington.
United States Patent |
3,783,276 |
Allington |
January 1, 1974 |
DUAL BEAM OPTICAL SYSTEM
Abstract
To compensate for variations in the intensity of light emitted
from different locations in or in different directions from a lamp,
a radiating member is located in one focus of an ellipsoidal
reflector to receive light from the lamp which is mounted with its
bright spot in the other focus of the ellipsoidal reflector and to
radiate in directions in line with a narrow dimension of the
radiating member two oppositely directed, proportional-intensity
beams of light through two aligned light-beam holes in the walls of
the ellipsoidal reflector on opposite sides of the radiating
member, with the radiating member having, in a first embodiment, a
surface that diffuses the light so that it is radiated with
proportional intensities into both beams in accordance with
Lambert's cosine law, in a second embodiment, a surface that
fluoreses light with proportional intensities into both beams, and
in a third embodiment, a surface with flourescent particles that
both diffuse the light and fluorese in response to it, all three
embodiments causing the beams of light to be of proportional
intensity. Interchangeable filters in the light beams of the third
embodiment are selected to pass either the diffused light or the
fluorescent light from the radiating member, thus enabling the
system to be used for different purposes by changing filters.
Inventors: |
Allington; Robert W. (Lincoln,
NB) |
Assignee: |
Instrumentation Specialties
Company (Lincoln, NB)
|
Family
ID: |
22986757 |
Appl.
No.: |
05/259,868 |
Filed: |
June 5, 1972 |
Current U.S.
Class: |
250/226;
250/208.2; 359/618 |
Current CPC
Class: |
G01N
21/255 (20130101) |
Current International
Class: |
G01N
21/25 (20060101); H01j 039/12 () |
Field of
Search: |
;250/204,71R,22R,230
;350/169,171 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dixon; Harold A.
Attorney, Agent or Firm: Carney; Vincent L.
Claims
What is claimed is:
1. Apparatus for directing light from a light source into a
plurality of paths, comprising;
a light-radiating member;
focusing means for focusing light from said light source onto a
spot on said light-radiating member, whereby a substantial amount
of light is radiated by said light-radiating member;
said spot on said light-radiating member including light-radiating
means for radiating light along at least a first and a second of
said paths from said spot in response to said focused light with a
substantially constant ratio of the intensity of the light in said
first path to the intensity of the light in said second path, which
ratio is substantially independent of fluctuations in the light
from said light source.
2. Apparatus according to claim 1 in which:
said light-radiating member is a passive light radiating means;
and
said passive light-radiating means includes means for substantially
diffusing light.
3. Apparatus according to claim 1 in which:
said light-radiating member is fluorescent means for emitting light
at a first frequency when impinged upon by light having a second
frequency; and
said light source includes means for emitting light of said second
frequency.
4. Apparatus according to claim 1 in which said light-radiating
member includes a means for substantially diffusing light.
5. Apparatus according to claim 4 in which said means for
substantially diffusing light comprises a plurality of
particles.
6. Apparatus according to claim 5 in which:
said plurality of particles comprise fluorescent means for emitting
light at a first frequency when impinged upon by light having a
second frequency;
said light source includes means for emitting light of said second
frequency, whereby diffused light of said second frequency and
fluorescent light of said first frequency are directed along said
plurality of paths.
7. Apparatus according to claim 6 further including:
a plurality of interchangeable filter mounting means;
each of said interchangeable filter mounting means being mounted in
a different one of said plurality of paths; and
said filter mounting means being adapted to receive filters
blocking a selected one of said first and second frequencies of
light.
8. Apparatus according to claim 7 in which said fluorescent means
comprises means for emitting light having a wavelength
substantially in the range of 270 to 290 nanometers, and said light
source is an ultraviolet lamp.
9. Apparatus according to claim 8 in which said filters include
means for blocking light having a wavelength substantially of 254
nanometers.
10. Apparatus according to claim 9 further including;
a plurality of photocells;
said photocells being sensitive to a predetermined frequency;
different ones of said photocells being mounted in line with
different ones of said filters and said paths; and
said filters including means for producing light of said
predetermined frequency in response to light substantially in the
wavelength range of 240 to 285 nanometers.
11. Apparatus according to claim 8 in which said filters include
means for blocking light having a wavelength substantially in the
range of 270 to 290 nanometers.
12. Apparatus according to claim 11 further including:
a plurality of photocells;
said photocells being sensitive to a predetermined frequency;
different ones of said photocells being mounted in line with
different ones of said filters and said paths; and
said filters including means for producing light of said
predetermined frequency in response to light substantially in the
wavelength range of 240 to 285 nanometers.
13. Apparatus according to claim 1 in which:
said focusing means includes an ellipsoidal reflector having first
and second foci;
said light-radiating member being located in said first focus of
said ellipsoidal reflector; and
said light source including means for emitting light from said
second focus of said ellipsoidal reflector.
14. Apparatus according to claim 13 in which said ellipsoidal
reflector includes;
a first section having internal walls defining a first hole;
a second section having internal walls defining a second hole;
said first hole, first path and light radiating member being
aligned; and
said second hole, second path and radiating means being
aligned.
15. Apparatus according to claim 13 in which:
said light-radiating member is a passive light-radiating means;
and
said passive light-radiating means includes means for substantially
diffusing light.
16. Apparatus according to claim 13 in which:
said light-radiating member is a fluorescent means for emitting
light at a first frequency when impinged upon by light having a
second frequency; and
said light source includes means for emitting light of said second
frequency.
17. Apparatus according to claim 14 in which said light-radiating
member includes a means for substantially diffusing light.
18. Apparatus according to claim 17 in which said means for
diffusing light comprises a plurality of particles.
19. Apparatus according to claim 18 in which:
said plurality of particles comprise fluorescent means for emitting
light at a first frequency when impinged upon by light having a
second frequency; and
said light source includes means for emitting light of a said
second frequency, whereby diffused light of said second frequency
and fluorescent light of said first frequency are directed along
said plurality of paths.
20. Apparatus according to claim 14 in which said light-radiating
means includes:
fluorescent means for emitting light at a first frequency when
impinged upon by light having a second frequency; and
said light source includes means for emitting light of said second
frequency.
21. Apparatus according to claim 19 in which:
said light-radiating member has at least first and second
surfaces;
said first and second surfaces being spaced at their nearest points
a distance less than any other distance between two opposite
surfaces of the light radiating member.
22. Apparatus according to claim 20 in which:
said light-radiating member has at least first and second
surfaces;
said first and second surfaces being spaced at their nearest points
a distance less than any other distance between two opposite
surfaces of the light radiating member.
23. Apparatus for directing light from a light source into a
plurality of paths, comprising:
a light-radiating member having at least first and second
surfaces;
said light-radiating member being capable of passing light;
said light-radiating member including light radiating means for
responding to light impinging on said member from said light source
by radiating light along at least a first of said paths from said
first surface and along a second of said paths from said second
surface with a substantially constant ratio of the intensity of the
light in said first path to the intensity of the light in said
second path, which ratio is substantially independent of
fluctuations in the light from said light source;
said first and second surfaces being spaced at their nearest points
a distance less than any other distance between two opposite
surfaces of the light-radiating member.
24. Apparatus according to claim 23 in which:
said light-radiating member is a passive light-radiating means;
and
said passive light-radiating means includes means for substantially
diffusing light.
25. Apparatus according to claim 23 in which said light-radiating
means includes a means for diffusing light.
26. Apparatus according to claim 25 in which said means for
diffusing light comprises a plurality of particles.
27. Apparatus according to claim 26 in which:
said plurality of particles comprise fluorescent means for emitting
light at a first frequency when impinged upon by light having a
second frequency; and
said light source includes means for emitting light of said second
frequency, whereby diffused light of said second frequency and
fluorescent light of said first frequency are directed along said
plurality of paths.
28. Apparatus according to claim 27 further including:
a plurality of interchangeable filter mounting means;
each of said interchangeable filter mounting means being mounted in
a different one of said plurality of paths; and
said filter mounting means being adapted to receive filters
blocking a selected one of said first and second frequencies of
light.
29. Apparatus according to claim 28 in which said fluorescent means
comprises means for emitting light having a wavelength
substantially in the range of 270 to 290 nanometers and said light
source is an ultraviolet lamp.
30. Apparatus according to claim 29 in which said filters include
means for blocking light having a wavelength substantially of 254
nanometers.
31. Apparatus according to claim 30 further including:
a plurality of photocells;
said photocells being sensitive to a predetermined frequency;
different ones of said photocells being mounted in line with
different ones of said filters and said paths; and
said filters including means for producing light of said
predetermined frequency in response to light substantially in the
wavelength range of 240 to 285 nanometers.
32. Apparatus according to claim 29 in which said filters includes
means for blocking light having a wavelength substantially in the
range of 270 to 290 nanometers.
33. Apparatus according to claim 32 further including:
a plurality of photocells;
said photocells being sensitive to a predetermined frequency;
different ones of said photocells being mounted in line with
different ones of said filters and said paths; and
said filters including means for producing light of said
predetermined frequency in response to light substantially in the
wavelength range of 240 to 285 nanometers.
34. Apparatus according to claim 23 in which said light-radiating
means includes:
fluorescent means for emitting light at a first frequency when
impinged upon by light having a second frequency; and
said light source includes means for emitting light of said second
frequency.
35. Apparatus according to claim 34 in which said fluorescent means
comprises a clear fluorescent crystal.
36. Apparatus according to claim 3 in which said fluorescent means
is a clear fluorescent means for emitting light at said first
frequency.
37. Apparatus according to claim 3 in which said fluorescent means
includes a plurality of particles for emitting light at said first
frequency.
38. Apparatus according to 16 in which said fluorescent means is a
clear fluorescent means for emitting light at said first
frequency.
39. Apparatus according to claim 16 in which said fluorescent means
includes a plurality of particles for emitting light at said first
frequency.
40. Apparatus according to claim 34 in which said fluorescent means
includes a plurality of particles for emitting light at said first
frequency.
41. Apparatus according to claim 1 further including at least first
and second photocells, said first photocell being positioned in one
of said plurality of paths and said second photocell being
positioned in another of said plurality of paths.
42. Apparatus according to claim 2 further including at least first
and second photocells, said first photocell being positioned in one
of said plurality of paths and said second photocell being
positioned in another of said plurality of paths.
43. Apparatus according to claim 3 further including at least first
and second photocells, said first photocell being positioned in one
of said plurality of paths and said second photocell being
positioned in another of said plurality of paths.
44. Apparatus according to claim 4 further including at least first
and second photocells, said first photocell being positioned in one
of said plurality of paths and said second photocell being
positioned in another of said plurality of paths.
45. Apparatus according to claim 5 further including at least first
and second photocells, said first photocell being positioned in one
of said plurality of paths and said second photocell being
positioned in another of said plurality of paths.
46. Apparatus according to claim 13 further including at least
first and second photocells, said first photocell being positioned
in one of said plurality of paths and said second photocell being
positioned in another of said plurality of paths.
Description
This invention relates to optical systems and more particularly
relates to apparatuses for generating and controlling beams of
light for use in optical systems.
For some purposes, it is desirable to generate a plurality of beams
of light of proportional intensities. One such purpose is to
compare the light absorbing characteristics of two substances. For
example, in liquid chromatography, a comparison is made between a
first beam of light transmitted through a solvent having solutes
separated into zones and a second beam of light transmitted through
pure solvent to locate the solutes by the difference in the light
absorbing characteristics between the solutes and the pure solvent.
The first and second beams of light should not change in intensity
with respect to one another except for changes caused by the
solutes.
The apparatus for generating the two beams of light generally
includes a primary light source and an optical system for forming
two beams of light from the primary light source.
Generally, the light supplied by the primary light source to some
locations in the optical system fluctuates in intensity with
respect to the light supplied to other locations. For example, the
light from mercury vapor ultraviolet lamps fluctuates for two
reasons: which are: (1) the light from one location within the lamp
has, under some circumstances, an intensity that fluctuates with
respect to the intensity of the light from another location within
the lamp; and (2) mercury vapor moves by convection within the
lamp, absorbing light that is being transmitted in the direction of
the optical system so that light following a first path within the
lamp on the way to one location in the optical system fluctuates in
intensity with respect to light following another path from the
same location within the lamp to another location in the optical
system because the relative amounts of absorption of light in the
two paths fluctuates.
In one type of prior art optical system, the primary light source
radiates light against a long side of an elongated cylindrical
fluorescent crystal, causing it to radiate fluorescent light from
two rounded ends in two opposite directions.
This prior art system has the disadvantage of providing light beams
that fluctuate in intensity with respect to each other under some
circumstances. The light beams fluctuate in intensity with respect
to each other when the light from the primary light source striking
the side of the crystal at one location fluctuates in intensity
with respect to the light striking another location since the light
transmitted along the crystal is attenuated more when traveling to
a more distant end than to a closer end, primarily as a result of
absorption within the crystal. causing the intensity of the light
beam emitted from one end of the crystal to be increased more than
the intensity the light beam from the other end of the crystal by
light striking the crystal at any point except the center of the
elongated side.
In another type of prior art optical system, the primary light
source is located in the focus of a large lens that collimates the
light, forming parallel beams of light from light originating at
the same location in the lamp.
This type of prior art also has the disadvantage of providing light
beams that fluctuate in intensity with respect to each other even
though the light in each beam originates generally from the same
location in the lamp. The light intensities of the two beams
fluctuate with respect to each other because the light in one beam
travels through a different path in the lamp from the path traveled
by the light in the other beam, resulting in fluctuations in the
relative amounts of light absorbed. Moreover, if the lens is not
properly focused on the light source, light from a wide area is
applied to the parallel beams of light, and when the light from one
portion of the wide area fluctuates with respect to light from
another portion of the wide area, the beams of light fluctuate in
intensity with respect to each other.
Accordingly, it is an object of the invention to provide a novel
optical system for controlling plural beams of light.
It is a further object of the invention to provide a novel
apparatus for maintaining the intensities of a plurality of light
beams in a constant ratio to each other.
It is a still further object of the invention to provide a novel
apparatus for radiating a plurality of beams of light having
proportional light intensities from opposite surfaces of a
radiating member having a dimension in line with the beams of light
that is very small compared with its dimension transverse to the
beams of light.
It is a still further object of the invention to provide a novel
apparatus for compensating for spatial variations in the intensity
of light from a light source.
It is a still further object of the invention to provide a plural
light beam optical system in which the ratios of the light
intensities of the different beams are independent of spatial
fluctuations of the intensity of the light eminating from the
primary light source.
It is a still further object of the invention to provide an
apparatus for generating plural light beams of high light
intensity.
It is a still further object of the invention to provide an
apparatus capable of providing plural beams of light, which beams
of light can be easily adjusted to provide a selected range of
frequencies or a selected spectral line.
It is a still further object of the invention to provide an
apparatus for producing a plurality of beams of light from a light
diffusing source.
It is a still further object of the invention to provide an
apparatus for producing a plurality of beams of light from a
fluorescent surface.
It is a still further object of the invention to provide an
apparatus for producing a plurality of beams of light from a
combined fluorescent and light diffusing source.
It is a still further object of the invention to provide an optical
system that includes ellipsoidal reflectors to focus light from a
wide spatial angle onto a secondary source from a primary source of
light.
It is a still further object of the invention to provide a dual
beam optical system that is easily adjusted for different
purposes.
In accordance with the above and further objects of the invention,
an optical system includes a source of light beams and a filtering
arrangement for selecting the same spectral line in each beam of
light for use in comparing the light absorbance characteristics of
two substances. The light beams are formed by focusing light from a
primary source of light on one spot or a radiating member and
forming or selecting two beams of light from the light radiated by
the radiating member.
To form the two beams of light, the source of light beams includes:
(1) an ellipsoidal reflector, having two sections, each with a
light-beam hole; (2) a primary source of light having its bright
spot in one of the foci of the ellipsoidal reflector; and (3) a
radiating member in the other end of the foci of the ellipsoidal
reflector, which radiating member transmits light in the direction
of the two light-beam holes in the two sections of the ellipsoidal
reflector. The radiating member is translucent and has a short
dimension, in the direction of the light-beam holes so that two
oppositely directed, proportional-intensity beams of light are
emitted from the ellipsoidal reflector having any one of three
arrangements, to radiate the light which are: (1) a light diffusing
surface; (2) a surface that fluoresces; or (3) a surface that
fluoresces and also diffuses light.
In operation, light from the primary source of light is reflected
onto the radiating member from a major portion of the solid angle
around the primary source of light by the ellipsoidal reflector
since the primary source of light is one focus and the radiating
member is in the other focus of the ellipsoidal reflector. The
light is diffused, causes fluorescence or is both diffused and
causes emission of fluorescent light upon impinging on the
radiating member, with the diffused light and the fluorescent
light, when present, leaving the ellipsoidal reflector in two
oppositely directed proportional-intensity beams of light through
the two light-beam holes in the sections of the reflector.
The two beams of light are of proportional intensity even though
the primary source of light may have spatial fluctuating
differences in the intensity of the light that it emits because
both diffused light and fluorescent light contribute to both beams
of light substantially proportionally regardless of the direction
of the light before being diffused or causing fluorescence and
because light is passed through the short width of the translucent
member without significant attenuation.
In an optical system in which the diffused light has a wavelength
of 254 nanometers and the fluorescent light has a wavelength of
between 270 and 290 nanometers, for example, the filter passes a
light having a wavelength of approximately 254 nanometers and
blocks light having wavelengths of between approximately 270 and
290 nanometers, a wavelength of 254 nanometers being useful in some
applications for dual beam optical systems. Another filter,
interchangeable with the one filter, passes light having a
wavelength of between 270 and 290 nanometers and blocks light
having a wavelength of about 254 nanometers, the wavelengths of
light between 270 and 290 nanometers being useful in other
applications for a dual beam optical system.
The above noted and other features of the invention will be better
understood from the following detailed description when considered
with reference to the accompanying drawings in which:
FIG. 1 is a plan view of apparatus embodying the invention;
FIG. 2 is a front elevational view of the apparatus of FIG. 1;
FIG. 3 is a side sectional view of the apparatus of FIG. 1 taken
substantially along the line 3--3 in the direction of the
arrows;
FIG. 4 is a side sectional view of the apparatus of FIG. 1 taken
substantially along the line 4--4 in the direction of the
arrows;
FIG. 5 is a sectional view of an interchangeable
wavelength-selecting light filter usable with the apparatus of FIG.
1; and
FIG. 6 is a graph showing the light absorbance of certain
components of the light filter.
GENERAL STRUCTURE AND OPERATION
In FIG. 1, there is shown, in a plan view, a dual beam optical
system 10 having as its principal parts a dual beam light source
12, first and second light absorbance cells 14 and 16, and first
and second light measuring cells 18 and 20.
The dual beam light source 12 is mounted by a base 22 in a central
location within a parallelepiped-shaped cabinet 24 and provides two
oppositely directed beams of light, with the first light absorbance
cell 14 being mounted between a first side of the dual beam light
source 12 and the first light measuring cell 18 and with the second
light absorbance cell 16 being mounted between a second side of the
dual beam light source 12 and the second light measuring cell 20.
The first side of the dual beam light source 12, the first light
absorbance cell 14 and the first light measuring cell 18 are
aligned in a first beam of light, with the first light measuring
cell 18 being mounted to a first side of the cabinet 24; and the
second side of the dual beam light source 12, the second light
absorbance cell 16, and the second light measuring cell 20 are
aligned in a second beam of light, with the second light measuring
cell 20 being mounted to a second side of the cabinet 24. To
provide access to the interior of the cabinet 24, its sides are
hinged at 26 and 28, permitting it to be easily opened for
assembly, repair and the replacement of parts when needed.
The dual beam optical system 10 is part of photometry apparatus of
the type requiring two matched beams of light. One such type of
photometry apparatus, for example, locates organic solutes such as
different proteins and amino acids and the like within a
chromatographic column during fractionating of the column.
In this type of apparatus, the different organic solutes are
located within the column by their different light absorbances,
which are determined by transmitting a first beam of light from a
dual beam source of light through the column containing the solute
and a second beam of light from the dual beam light source through
a sample of the solvent and comparing the intensities of the light
in the two beams after they have been passed through the solute and
pure solvent. However, it is understood that there are other
specific uses for the dual beam optical system 10 known to persons
skilled in the art.
In the operation of the dual beam optical system 10, the first beam
of light from the dual beam light source 12 impinges on the first
light measuring cell 18 after passing through the first light
absorbance cell 14 containing a solute to be located in a
chromatographic column or to have its concentration determined and
the second beam of light from the dual beam light source 12
impinges on the second light measuring cell 20 after passing
through the second light absorbance cell 16 containing only the
solvent. The first and second light measuring cells generate first
and second electrical signals respectively in response to the light
that impinges upon them and these signals are compared to provide a
comparison between the light absorbance characteristics of the
substances in the first and second light absorbance cells. This
comparison may be made by a circuit of the general type disclosed
in U.S. Pat. No. 3,463,927 to Robert W. Allington for "Apparatus
for Measuring Absorbance Differences."
DETAILED STRUCTURE
The dual beam light source 12 includes a lamp 30, a light intensity
balancer 32, and a two-sector ellipsoidal reflector 34, with the
two-sector ellipsoidal reflector 34 having a first sector 36 and a
second sector 38.
To provide light for the first and second uniform beams of light,
the lamp 30 is mounted to the base 22, which services as a socket
for electrical connection and is centrally located within the dual
beam light source 12. The lamp 30 serves as a primary light source
and may be any of several different types, the particular type
generally being selected for its abaility to provide light of the
desired frequency.
In the preferred embodiment, the lamp 30 is a low pressure mercury
vapor lamp that emits ultraviolet light which is particularly
useful in some photometric apparatuses such as those that measure
or compare the optical density or light absorbance of certain
solutions containing organic materials such as protein, amino acid
or the like. However, other types of lamps may be used as a primary
light source for other purposes. This invention has particular
utilty in photometric apparatuses in which the light emitted from
some locations in the primary light source fluctuates in intensity
with respect to light emitted from other locations or in which
light emitted in some directions fluctuates in intensity with
respect to light emitted in other directions.
To focus light from the lamp 30 into two oppositely directed beams,
the ellipsoidal reflector 34 has the general shape of a prolate
spheriod with each of the two sectors 36 and 38 being a section of
the spheroid, spaced from the other sector at the center of the
reflector 34 and having its concave side facing the concave side of
the other. As best shown in FIG. 4, the bright spot of the lamp 30
is located in a first focus of the ellipsoidal reflector 34 to
focus light on the second focus and the light intensity balancer 32
is located in the second focus, with each of the two sectors 36 and
38 having a different one of two light-beam holes aligned with each
other and with the second focus to permit the first and second
proportional-intensity oppositely directed beams of light to leave
the ellipsoidal reflector 34, one of the light-beam holes being
shown at 40 in FIG. 4.
Because the light-beam holes are aligned with the second focus of
the ellipsoidal reflector 34 and with each other, light is not
directly reflected in a straight line from one sector through the
light intensity balancer 32 and the hole in the other sector into a
light absorbance cell without being adequately diffused since there
is no such light path, all straight paths of light from one
reflector through the hole of the other reflector being at an angle
with the first and second beams of light. Moreover, in one
embodiment, the light-beam holes are each closed by a different
lens that focuses on the light-intensity balancer 32 so as to
increase the intensity of light transmitted to the light absorbance
cells and to reduce the differences in intensity between the first
and second beam by preferentially transmitting light from the
screen, which is at the foci of the two lenses.
Generally the ellipsoidal reflector performs two functions, which
are: (1) to focus light from the lamp 30 onto the light intensity
balancer 32; and (2) to pass two oppositely directed beams of light
from the light intensity balancer 32 to the light absorbance cells
14 and 15, which beams do not include light reflected directly from
one reflector through the light intensity balancer and along the
beam in a straight path, light along the latter direct path
creating time-varying inequalities in the light intensity of the
two oppositely directed beams of light under some circumstances
because the light reflected in this straight path may not be
adequately diffused by the light intensity balancer. While
ellipsoidal reflectors are well suited for these purposes, other
types of reflectors and lens are available which other types can be
used for the same purposes when properly constructed.
To cause the two oppositely directed light beams to have
intensities that are in a constant ratio to each other even when
the intensity of the light emitted by the lamp 30 varies over a
period of time from location to location in the lamp or from
direction to direction, the light intensity balancer 32 includes a
transparent or translucent base with a flat light radiating portion
42 (FIG. 3) mounted in one of the foci of the ellipsoidal reflector
34, the bright spot of the lamp 30 being mounted in the other of
the foci. The flat light radiating portion is aligned with both
light-beam holes in the sections 36 and 38 of the ellipsoidal
reflector 34 in such a manner that a straight line through both
light-beam holes is perpendicular to the flat light radiating
portion.
To cause the intensities of the light in the light beams to be
always in the same proportion, the light radiating portion 42 of
the light intensity balancer 32 may include, in general, any
surface or combination of surfaces that radiates light
proportionally into a plurality of beams. In the preferred
embodiment of the inventin, two beams of light are radiated in
opposite directions through light-beam holes, and in this
embodiment, no lens is necessary to focus the light into beams from
the light radiating member since the beams are permitted to pass
through the light-beam holes in opposite directions, thus removing
the possibility of noise in the light caused by a poorly focused
lens that applies light from too large an area into the beams.
Because the light is directed into two opposite directions, the
light radiating member should have its smallest dimension parallel
to the light beams and this dimension should be sufficiently small
to avoid any significant attenuation of the light passing through
the light radiating member. Generally, it is less than one
millimeter thick. Usually, the performance improves if it is
translucent enough so that it radiates equally in both directions
regardless of which section of the ellipsoidal reflector supplies
the light that impinges upon it.
In one embodiment, the light radiating portion 42 includes for this
purpose a translucent light diffusing surface having a passive
light radiating means such as in a layer sufficiently thin to be
translucent or having other light scattering deformations. Herein,
a passive light radiating means does not emit light by the changes
in the state of excitation of its atoms or molecules such as
happens in incandescent or fluorescent radiators but only
re-radiates light.
The light diffusing surface scatters light incident upon it in a
random manner, causing the light to be radiated in accordance with
Lambert's cosine law, with the intensity being proportional to the
cosine of the angle with respect to a normal to the light diffusing
surface regardless of its location of origin in the lamp 30.
Accordingly, the ratio intensity of the light in the beams is
constant because the beams are all at a constant angle to the
emitting surface. Moreover, because the light equalizing portion of
the light intensity balancer is translucent and does not absorb
much light, light from each one of the sectors 36 and 38 is
re-radiated from both sides of the light intensity balancer 32 to
contribute to both the first and the second beams of light and
thereby further equalize the beams of light.
In another embodiment, the light equalizing portion 42 includes for
this purpose fluorescent particles in a layer sufficiently thin to
be translucent or a transparent sheet of fluorescent material
mounted to the transparent or translucent base plate of the light
intensity balancer 32. The fluorescent particles or sheet emit
light in all directions so that each point contributes
proportionately to the first and the second beams of light. The
fluorescent particles, when used, also create a diffusing surface,
causing diffused light of the frequency emitted by the lamp 30 as
well as light emitted by fluorescense of the particles to be
directed into the first and second beams of light. The light
absorbed by the fluorescent particles reduce the constant-ratio
effect some, but the performance is still adequate for most
purposes.
The frequencies to be passed through the light absorbance cells 14
and 16 and to photocells within the light measuring cells 18 and 20
are selected by including filters in the path of the beams of light
to selectively absorb those frequencies of light that are not to be
passed to the photocells. Since the filters are easily changed, the
presence of two different ranges of frequencies of light, one from
fluorescence of the particles and the other from diffusion of
light, each of which is useful in a different application of the
dual beam optical system, enables the dual beam optical system to
be easily adapted to different applications.
Another manner of constructing the dual beam optical system so that
it can be easily adapted to different applications is to provide
for easy selection of different frequencies for the light beams. To
accomplish this in one embodiment (not shown) the light intensity
balancers are readily replaceable so that any of several light
intensity balancers, each having different fluorescent materials
that emit light at different frequencies, may be selected for use
in the dual beam optical system. In another embodiment (not shown)
the light intensity balancers are readily adjustable in position
within the ellipsoidal reflector and include a plurality of
different fluorescent materials at different locations that emit
light at different frequencies. The light intensity balancers are
adjusted to position a selected one of the different fluorescent
materials into the focus of the ellipsoidal reflector to select the
frequency of light to be emitted into the beams. Of course, in both
of these embodiments, the light filters are selected in accordance
with the frequencies that are to be used.
In the preferred embodiment, the substrate of the light intensity
balancer 32 is quartz because quartz is transparent to ultraviolet
light which is especially useful in the preferred embodiment.
However, other materials can obviously be used as the
substrate.
There are many known methods for fastening particles to the surface
of a substrate or for deforming a substrate to cause it to diffuse
light. For example, particles may be mounted by precipitation of an
adhesive binder or between two sections of a substrate. The
substrate may be deformed by scratching or roughening its surfaces
to cause it to diffuse light when particles are not fastened to
it.
Particularly useful fluorescent materials for the light intensity
balancer 32 are microcrystalline lanthanum fluoride with cerium
activation as described in U.S. Pat. No. 2,450,548 to Gishoff or
calcium lithium silicate, lead activated phosphor.
As best shown in FIG. 2, the light absorbance cells 14 and 16 each
include a different respective one of the two rectangular housings
44 and 46 enclosing respective ones of two, transparent, tubular,
generally Z-shaped passageways, with each passageway including: (1)
a respective one of the vertical entrance channels 48 and 50
extending from a point below the dual beam light source 12 in a
direction parallel to the light intensity balancer 32 to a point
opposite to respective ones of the light-beam holes in the sectors
36 and 38; (2) a respective one of the two light absorbing channels
52 and 54 extending in a direction aligned with the light-beam
holes and with the first and second beams of light; and (3) a
respective one of the two outlet channels 56 and 58 extending
vertically from points opposite to the light-beam holes parallel to
the light intensity balancer 32 to points above the dual beam light
source.
To permit the first and second beams of light from the dual beam
light source 12 to pass from the light-beam holes through the light
absorbing channels 52 and 54, the light absorbing channel 52 has a
transparent window 60 on one side and a transparent window 62 on
the other side aligned with the light-beam holes to permit light to
pass through the housing 44, and the light absorbing channel 54 has
a transparent window 64 on one side and a transparent window 66 on
the other side aligned with the light-beam holes to permit light to
pass through the housing 46, with one end of each of the channels
52 and 54 and each of the transparent windows 62 and 64 being
adjacent to different ones of the two light-beam holes.
To measure the light absorbance or transmittance of the fluid in
the light absorbance cells 52 and 58, the first and second light
measuring cells 18 and 20 receive the first and second beams of
light respectively after they have passed through the light
absorbance channels 52 and 54 of the first and second light
absorbance cells 14 and 16. Each of the first and second light
measuring cells 18 and 20 includes a different one of the filters
68 and 70 and a different one of the two photocells 72 and 74,
mounted in positions aligned with the first and second beams of
light so that the first and second beams of light each pass through
one of the filters 68 and 70 before exciting a respective one of
the two photocells 72 and 74.
The photocells 72 and 74 are part of a circuit for comparing the
light impinging upon them and providing an indication of the
relative optical density of the fluid in the light absorbance cells
14 and 16 for the purpose of locating or identifying a solute in
the fluid flowing through one of the light absorbance cells as
described in greater detail in the aforementioned U.S. Pat. No.
3,463,927. The filters are similar in some respects to those
described in U.S. Reissue Pat. No. 26,638.
In FIG. 5, there is shown, in a sectional view, the filter 68,
which will be described in greater detail hereinafter, the filter
70 being substantially identical to the filter 68 and not requiring
a separate description. Generally the filters include a combination
of filter elements, a light filtering liquid, and a fluorescent
element, with: (1) one filter element and the light filtering
liquid transmitting one wavelength of light that has been used for
measuring the absorbance of the substance in a light absorbing cell
to the fluorescent element and blocking other wavelengths including
the wavelength emitted by the fluorescent element; (2) the
fluorescent element emitting light of another wavelength in
response to this one wavelength, which other wavelength is one to
which the photocell is sensitive; and (3) a third filter element
blocking the undesired wavelengths passed by the one filter element
and the light filtering liquid, and passing the wavelength emitted
by the fluorescent element. Superior selection of the one
wavelength is provided by this combination.
More specifically, the filter 68 includes a generally cylindrical
tubular casing 76 having at one end a disc-shaped front face 78
with a centrally located disc-shaped opening in it and having the
opposite and open to receive filter and fluorescent elements, the
internal walls of the casing 76 being threaded. To enable the
tubular casing 76 to be readily attached to the first light
measuring cell 18, its cylindrical surface is provided with a
cylindrical shoulder at one end adjoining the front face 78 and is
provided with an annular notch 80 near its other end so that the
casing 76 is received within a cylindrical opening in the first
light measuring cell 18 and held thereto by a detent within the
annular notch 80 with the shoulder supporting the face 78 outside
of the cylindrical opening.
Within the tubular casing 76, are two filter elements 82 and 84 and
a fluorescent element 86, each having a portion aligned with the
opening in the front face 78 to receive light from the first beam
of light. Moreover, a light-filtering liquid is contained at 88
within the filter 68 so that the light-beam passes through it
before reaching the photocell 72 (FIG. 2).
To hold the filter elements 82 and 84, the fluorescent element 86
and the light-filtering liquid at 88 in place, the filter 68
includes a transparent quartz window 90 closing the disc-shaped
central opening in the front face 78, an O-ring 92 pressing against
the transparent glass window 90 to form a liquid tight seal
therewith, a cylindrical spacer 94 pressing the filter element 82
against the other side of the 0-ring 92 to form a liquid tight
compartment for the light-filtering liquid at 88, and a retaining
ring 96 threadedly engaging the internal threads of the tubular
housing 76 to hold the spacer against the filter element 82 and to
support the filter element 84 and the fluorescent element 86.
The filter elements 82 and 84, the fluorescent element 86 and the
light-filtering liquid at 88 are selected to eliminate response to
frequencies of light from the first light beam except light of a
predetermined spectral line that is useful as a measure of the
light absorbance of transmittance characteristic of a solute in the
light absorbance cell and to provide light having a wavelength to
which the photocell is especially sensitive which light has an
intensity proportional to the intensity of the light in the
selected spectral line. The selection may be made from a wide range
of filter elements, liquids and fluorescent elements depending on
the spectral line that is to be used in a particular application
and the choice of photosensitive devices to measure the light
emitted by the fluorescent element.
In one embodiment of filter 68, particularly useful in locating or
identifying some organic materials, the filter element 84 transmits
green visible light produced by the fluorescent element 86, with:
(1) the filter element 82 being red purple silica which transmits
light in the ultraviolet region to as short a wavelength as 240
nanometers, and absorbs green visible light: (2) the filter element
84 being a filter which absorbs ultraviolet light and transmits
only green light; and (3) the element 86 being a fluorescent
phosphor which produces green fluorescent light when radiated with
ultraviolet light having a wavelength shorter than some wavelength
slightly longer than 280 millimicrons such as a wvelength shorter
than 285 or 290 millimicrons. Together the filter elements 82 and
84 and the fluorescent element 86 produce green visible light, in
response to light in the wavelength range of 240-290
nonometers.
To obtain light having a wavelength of substantially 280 nanometers
from the light produced by a light equalizing portion of the light
intensity balancer 32 that includes microcrystalline lanthanum
fluoride with cerium activation or calcium lithium silicate lead
activated phosphor, a light-filtering liquid is included at 88 that
transmits light having a wavelength longer than 280 nanometers and
absorbs light having a wavelength of 254 nanometers. On the other
hand, to obtain light having a wavelength of 254 nanometers from
the same source of light, a light-filtering liquid is included at
88 which transmits light of 254 nanometers and absorbs fluorescent
light over the wavelength region of 270 to 300 nanometers.
Although solid materials having the filtering characteristics
needed to produce the frequency response required for the above two
embodiments are rare, light-filtering liquids are readily
available. In FIG. 6 there is shown a graph including a first curve
98 and a second curve 100 having ordinates of the absorption of
light and abscissae of the wavelength of the light absorbed for two
liquids, with the first curve 98 representing a light-filtering
liquid that selectively transmits light having a wavelength of 254
nanometers and blocks light having wavelengths between 270 and 290
nanometers and with the curve 100 representing a light-filtering
liquid that selectively transmits light having a wavelength between
270 and 290 nanometers and blocks light having a wavelength of 254
nanometers. A dilute solution of carbon disulfide has a absorbance
spectrum resembling that of curve 98 and a solution of benzene in a
transparent solvent has a characteristic resembling that of curve
100 although it also has several other features in its
characteristic curve, not shown in curve 100, that are significant
to this invention. There are also other suitable liquids.
DETAILED OPERATION
Before operating the dual beam optical system 10, the filters 68
and 70 are prepared and inserted into the first and second light
measuring cells 18 and 20 (FIG. 2). Generally, the filters are
prepared for use in accordance with the type or types of organic
solutes that are to be located in a chromatographic column that is
flowing through the first light absorbance cell 44, but, of course,
the filters are chosen according to other criteria for other
applications of the dual beam optical system.
To detect a solute that absorbs light having a wavelength of 254
nanometers, the filter 68 is assembled as shown in FIG. 5 with a
liquid such as a dilute solution of carbon disulfide included at
88. To detect a solute that absorbs light having a wavelength of
between 270 and 290 nanometers, the filter is assembled in the same
manner but with a liquid such as a solution of benezene in a
transparent solvent at 88.
In the operation of the dual beam optical system 10, a solvent
containing a solute is pumped through the light absorbance cell 14
and pure solvent is pumped through the second light absorbance cell
16. While the solute is flowing through the light absorbing channel
52 of the first light absorbance cell 14 and the pure solvent is
flowing through the light absorbing channel 58 of the second light
absorbance cell 16, the first beam of light is transmitted through
the light absorbing channel 52 to the first light measuring cell 18
and the second beam of light is transmitted through the light
absorbing channel 58 to the second light measuring cell 20, with
the first and second beams of light having proportional light
intensities. The first light measuring cell 18 and the second light
measuring cell 20 compare the intensity of the light in the first
and second beams of light to obtain information about the solute
flowing through the first light absorbing channel 52.
To generate the first and second beams of light, the lamp 30
radiates light, which in the preferred embodiment is ultraviolet
light, onto the light intensity balancer 32. Since the bright spot
of the lamp 30 is in one focus and the light radiating portion 42
of the light intensity balancer 32 is in the other focus of the
ellipsoidal reflector 34, light from a solid angle that is the
major portion of a sphere is radiated from the lamp 30 to the light
radiating portion 42 of the light intensity balancer 32.
In a first embodiment of the ellipsoidal reflector 34, the light
radiating portion 42 of the light balancer 32 is a translucent
diffusing surface that diffuses the light radiated to it and
re-radiates it as two oppositely directed beams through the two
light-beam holes in the first and second reflector sections 36 and
38. The light is radiated from the light radiating portion 42 in
accordance with Lambert's cosine law with light impinging upon each
spot causing proportional radiation into both the first and second
beams of light so that both beams have proportional light
intensities. Because the two light-beam holes are in line with the
first and second beams of light, no light can be directly reflected
from one reflector section through the light radiating portion and
into the light beam opposite from the reflector section without
being diffused.
In a second embodiment, the light radiating portion 42 of the light
balancer 32 includes a thin transparent or translucent layer of
fluorescent particles; which defuses light and fluoresces, with the
diffused light making proportional contributions to each of the
first and second beams of light as in the first embodiment and with
the fluorescent light making proportional contributions to each of
the first and second beam of light of another frequency because the
radiation of the particles from fluorescense is independent of the
direction of the light causing the fluorescence.
After the light from the first and second beams of light pass
through the first and second light absorbance cells 14 and 16, they
impinge on the first and second light measuring cells 18 and 20,
where they pass through filters that select a single spectral line
to transmit to photocells which develop signals related to the
amount of light absorbed by the solute and solvent. The filters are
selected in accordance with the particular application of the dual
beam optical system as explained above.
From the above description, it can be understood that the dual beam
optical system of this invention has several advantages, such as:
(1) it provides closely matched beams of light even if the lamp
that is the primary source of the light has spatial time-varying
discrepancies or directional discrepancies in the intensity of the
light; and (2) the two beams of light are bright, making use of a
high percentage of the light from the primary source of light.
Although a specific embodiment of the invention has been described
with some particularity, many modifications and variations in the
embodiment are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described without departing from the invention.
* * * * *