Circular-dichroism measurement system characterized by noise cancellation

Claim 2

In a circular-dichroism measurement system, the combination comprising means including a light source to effect simultaneous passage of two predominantly circularly polarized light beams of opposite sense through a sample whose circular-dichroism is to be measured, light-sensitive means operable in response to simultaneous interception of the respective beams to produce corresponding electrical currents each of which is characterized by signal and noise components, certain noise components being generated by operation of said light-sensitive means, and other means responsive to said electrical currents to produce logarithmic versions thereof and to combine said versions for substantially reducing said noise components and for producing a resultant signal corresponding to the circulardichroism of the sample.

Claim 3

The combination of claim 1 wherein said light-sensitive means comprises the respective photocathodes of two photomultipliers located to intercept the respective beams and said electrical currents consist of electrons emitted from said photocathodes.

Claim 4

The combination of claim 2, wherein said other means comprises, in association with each said photomultiplier: feedback circuitry, connected between an output electrode and a dynode voltage input of that photomultiplier, and characterized as operating to maintain substantially constant an amplified output appearing at said output electrode, whereby dynode voltage at said dynode voltage input varies as a substantially logarithmic function of the corresponding one of said electrical currents.

Claim 5

The combination of claim 3 wherein said other means includes first and second channels respectively connected to said dynode voltage inputs, said logarithmic versions being transmitted on said channels.

Claim 6

The combination of claim 4 wherein one of said channels includes an inverter for inverting the phase of the logarithmic version associated therewith.

Claim 7

The combination of claim 5 wherein said other means includes a combiner connected with said channels for combining said logarithmic versions.

Claim 8

Apparatus comprising: means defining a zone adapted to receive a sample; illuminating means for simultaneously passing through said zone two predominantly circularly polarized light beams of opposite sense; detector means disposed to receive said beams after passage through said zone, and for producing two electrical currents corresponding respectively to the intensities of said beams after said passage; electrical means for receiving said electrical currents and producing electrical signals respectively substantially linearly related to the logarithms of said intensities; and display means, responsive to said signals, for indicating a measured value of circular-dichroism of a sample which may be placed in said zone.

Claim 9

Apparatus comprising: means defining a zone adapted to receive a sample; illuminating means for simultaneously passing through said zone two predominantly circularly polarized light beams of opposite sense; detector means disposed to receive said beams after passage through said zone, and for producing two electrical currents corresponding respectively to the intensities of said beams after said passage; electrical means for receiving said electrical currents and producing electrical signals respectively substantially linearly related to the logarithms of said intensities; and display means, responsive to said signals, for indicating a measured value of circular-dichroism of a sample which may be placed in said zone.

Claim 10

The apparatus of claim 7, wherein said illuminating means cyclically reverses the sense of each of said beams, substantially simultaNeously; and also comprising signal-coupling means for receiving said electrical signals and isolating a time-varying part thereof for transmission to said display means.

Claim 11

The apparatus of claim 7, wherein said illuminating means comprises: a light source; polarizer means for receiving light from said source and producing from said light two orthogonally linearly polarized beams; and optical retarder means characterized by variably linear birefringence, receiving said linearly polarized beams and converting the same into said two predominantly circularly polarized beams of opposite sense. 10. The apparatus of claim 7, wherein: said detector means comprises a pair of photosensitive surfaces; and said electrical means comprises: a pair of amplifier means, each connected to receive a corresponding one of said electrical currents from one of said photosensitive surfaces, and each said amplifier means producing an amplified output related by a respective amplification factor to the respective electrical current; a pair of means for establishing each of said amplification factors independently; and means for independently producing two control signals to control said amplification-factor-establishing means; each said amplification-factor-establishing means being characterized by an approximately logarithmic relation between said control signal and said electrical signal, within a range of operation; each said control-signal-producing means being responsive to a corresponding one of said amplified outputs, and varying said control signal to maintain said amplification factor at a time-varying level characterized in that said amplified signal maintains a substantially constant predetermined value; and said electrical signals being derived from said control signals.

Claim 12

The apparatus of claim 10, wherein; each said amplifier means comprises a photomultiplier having a photocathode, dynodes and an anode; each said photosensitive surface is a photocathode in the corresponding photomultiplier; each said electrical current is an electron stream ejected from the corresponding photocathode; each said amplified output appears at an electrode selected from the group consisting of said dynodes and said anode; each said amplification-factor-establishing means comprises said dynodes, and apparatus for making electrical connection thereto; each said control-signal-producing means comprises a source of voltage for establishing voltage difference between at least one dynode in the corresponding photomultiplier and at least one other such dynode in the same photomultiplier; each said voltage difference is the corresponding said control signal to which said display means is responsive; and each said control-signal-producing means comprises an amplifier responsive to the corresponding said amplified output at the corresponding said electrode, to regulate the corresponding said source of voltage to maintain said amplified output substantially constant.

Claim 13

Apparatus for the measurement of circular-dichroism in a sample, comprising: means including a source of light for producing two beams of light having intensities respectively proportional to characteristic transmission values of such sample for predominantly right- and predominantly left-circularly polarized light; detector means, disposed to simultaneously receive said beams and to produce electrical currents respectively proportional to said intensities; said currents being characterized in part by the presence of noise components unrelated to said dichroism, some of said noise components arising in said source of light, and others of said noise components arising through operation of said detector means; electrical means for receiving said electrical currents and producing electrical signals respectively substantially linearly related to the logarithms of said electrical currents, and for combining said electrical signals after a relative polarity inversion, of one of said signals whereby said noise components are substantially reduced; and means responsive to said electrical signals for indicating measured values of such dichroism.

Claim 14

Apparatus for the measurement of circular-dichroism in a sample, comprising: means including a source of light for producing two beams of light having intensities respectively proportional to characteristic transmission values of such sample for predominantly right- and predominantly left-circularly polarized light; detector means, disposed to simultaneously receive said beams and to produce electrical currents respectively proportional to said intensities; said currents being characterized in part by the presence of noise components unrelated to said dichroism, some of said noise components arising in said source of light, and others of said noise components arising through operation of said detector means; electrical means for receiving said electrical currents and producing electrical signals respectively substantially linearly related to the logarithms of said electrical currents, and for combining said electrical signals after a relative polarity inversion, of one of said signals whereby said noise components are substantially reduced; and means responsive to said electrical signals for indicating measured values of such dichroism.

Claim 15

The apparatus of claim 7, wherein a circularly dichroic sample may be placed in said zone so that said beams passing through said zone pass simultaneously through said sample, said beams being unequally reduced in intensity by such passage.

Claim 16

The apparatus of claim 8, wherein: a circularly dichroic sample is placed in said zone so that said beams passing through said zone pass simultaneously through such sample, beams having opposite circular polarization sense being unequally reduced in intensity by such passage; and said time-varying part arises from coaction of said cyclically reversing with said unequal reducing.

Claim 17

The apparatus of claim 7, wherein: said illuminating means comprises a light source for producing two beams, each comprising predominantly circularly polarized constituents of opposite sense in equal magnitude for passage through said zone; and comprising: optical retarder means characterized by variable linear birefringence, disposed to receive said beams after passage through said zone, and to derive from at least some of said circularly polarized constituents two elliptically polarized beams; and polarizing means disposed to receive said elliptically polarized beams and derive therefrom at least one plane-polarized beam for transmission to said detector means.

Claim 18

Apparatus comprising: a source of substantially randomly polarized light of a relatively wide band of wavelengths; a monochromator disposed to receive said light and select therefrom selected light of a relatively narrow band of wavelengths, said band having a nominal wavelength; a polarizer, disposed to receive said selected light and to derive therefrom two substantially linearly polarized beams polarized mutually orthogonally; an element having cyclically varying linear birefringence, disposed to receive said polarized beams from said polarizer and to form therefrom two elliptically polarized beams of opposite sense, whose ellipticity varies cyclically in correspondence with said cyclically varying birefringence, elliptically polarized light being understood to be composed of unequal amounts of circularly polarized light of opposite sense; means defining a sample zone for simultaneous passage therethrough of both said elliptically polarized beams of light, whereby any circular-dichroic characteristic of a sample which may be positioned in said zone is manifested as unequal reduction of the intensities of both said elliptically polarized beams of opposite sense in the course of simultaneous passage through said zone, and in turn whereby the intensities of said unequally reduced beams vary cyclically in accordance with said varying ellipticity and said dichroic characteristic; two photomultiplier each disposed to receive one of said elliptically polarized beams, and to produce in response thereto an electrical signal whose magnitude is substantially proportional to the intensity of said elliptically polarized beam, whereby said magnitude varies cyclically in correspondence with said cyclically varying ellipticity and said dichroic characteristic; dynode voltage supply means for independently activating and controlling the amplification of each of said photomultipliers, said activating and said controlling of each said photomultiplier proceeding substantially independently of said activating and said controlling of the other said photomultiplier, and said activating and controlling being characterized by application to each said photomultiplier of a dynode voltage; a pair of electrical amplifier means each connected to receive one of said electrical signals, and to regulate the corresponding one of said dynode voltage supply means so as to maintain the corresponding said electrical signal substantiAlly constant and at a predetermined level; whereby a time-varying part of each said dynode voltage represents the circular-dichroism of a sample placed in said zone, except for the inclusion in said time-varying part of unwanted noise components unrelated to said dichroism; and means for combining additively said two time-varying parts with a polarity inversion of one of said parts relative to the other, to produce an improved representation of said circular-dichroism characterized by substantially reduced relative magnitudes of said unwanted noise components.

Claim 19

Apparatus comprising: a source of substantially randomly polarized light of a relatively wide band of wavelengths; a monochromator disposed to receive said light and select therefrom selected light of a relatively narrow band of wavelengths, said band having a nominal wavelength; a polarizer, disposed to receive said selected light and to derive therefrom two substantially linearly polarized beams polarized mutually orthogonally; an element having cyclically varying linear birefringence, disposed to receive said polarized beams from said polarizer and to form therefrom two elliptically polarized beams of opposite sense, whose ellipticity varies cyclically in correspondence with said cyclically varying birefringence, elliptically polarized light being understood to be composed of unequal amounts of circularly polarized light of opposite sense; means defining a sample zone for simultaneous passage therethrough of both said elliptically polarized beams of light, whereby any circular-dichroic characteristic of a sample which may be positioned in said zone is manifested as unequal reduction of the intensities of both said elliptically polarized beams of opposite sense in the course of simultaneous passage through said zone, and in turn whereby the intensities of said unequally reduced beams vary cyclically in accordance with said varying ellipticity and said dichroic characteristic; two photomultiplier each disposed to receive one of said elliptically polarized beams, and to produce in response thereto an electrical signal whose magnitude is substantially proportional to the intensity of said elliptically polarized beam, whereby said magnitude varies cyclically in correspondence with said cyclically varying ellipticity and said dichroic characteristic; dynode voltage supply means for independently activating and controlling the amplification of each of said photomultipliers, said activating and said controlling of each said photomultiplier proceeding substantially independently of said activating and said controlling of the other said photomultiplier, and said activating and controlling being characterized by application to each said photomultiplier of a dynode voltage; a pair of electrical amplifier means each connected to receive one of said electrical signals, and to regulate the corresponding one of said dynode voltage supply means so as to maintain the corresponding said electrical signal substantiAlly constant and at a predetermined level; whereby a time-varying part of each said dynode voltage represents the circular-dichroism of a sample placed in said zone, except for the inclusion in said time-varying part of unwanted noise components unrelated to said dichroism; and means for combining additively said two time-varying parts with a polarity inversion of one of said parts relative to the other, to produce an improved representation of said circular-dichroism characterized by substantially reduced relative magnitudes of said unwanted noise components.

Claim 20

Apparatus for the measurement of circular-dichroism, comprising: means defining a zone to receive a sample; illuminating means, including a source of light, for concurrently passing through said zone two predominantly circularly polarized light beams of opposite sense; detection and display means disposed to receive said beams after concurrent passage through said zone, and to respond thereto by indicating a measured value of circular-dichroism for said zone, and in such a manner that fluctuations in light intensity which are common to said two beams mutually cancel at least in part in operation of said detection and display means and have reduced effect on said measured value; whereby fluctuations in operation of said light source affect said measured value to a lesser extent than they affect each of said two beams individually.

Claim 21

Apparatus for the measurement of circular-dichroism, comprising: means defining a zone to receive a sample; illuminating means, including a source of light, for concurrently passing through said zone two predominantly circularly polarized light beams of opposite sense; detection and display means disposed to receive said beams after concurrent passage through said zone, and to respond thereto by indicating a measured value of circular-dichroism for said zone, and in such a manner that fluctuations in light intensity which are common to said two beams mutually cancel at least in part in operation of said detection and display means and have reduced effect on said measured value; whereby fluctuations in operation of said light source affect said measured value to a lesser extent than they affect each of said two beams individually.

Claim 22

Apparatus for the measurement of circular-dichroism, comprising: means defining a sample zone; illuminating means, including a source of light, for concurrently passing through said zone two predominantly circularly polarized light beams of opposite sense; detector means disposed to receive said beams after passage through said zone, and to produce two electrical currents corresponding respectively to the intensities of said beams after said passage; and electrical processing means and display means for receiving and combining said electrical currents to indicate a measured value of circular-dichroism for said zone, and characterized in that fluctuations in current magnitude which are common to said two electrical currents mutually cancel at least in part and have a reduced effect on said measured value; whereby fluctuations in operation of said light source affect said measured value to a lesser extent that they affect each of said two electrical currents individually.

Claim 23

Apparatus for the measurement of circular-dichroism, comprising: means defining a sample zone; illuminating means, including a source of light, for concurrently passing through said zone two predominantly circularly polarized light beams of opposite sense; detector means disposed to receive said beams after passage through said zone, and to produce two electrical currents corresponding respectively to the intensities of said beams after said passage; and electrical processing means and display means for receiving and combining said electrical currents to indicate a measured value of circular-dichroism for said zone, and characterized in that fluctuations in current magnitude which are common to said two electrical currents mutually cancel at least in part and have a reduced effect on said measured value; whereby fluctuations in operation of said light source affect said measured value to a lesser extent that they affect each of said two electrical currents individually.

Claim 24

The apparatus of claim 17, wherein said illuminating means cyclically reverses the sense of each of said beams, substantially simultaneously; and said processing means comprises signal-coupling means for receiving said electrical signals and isolating a time-varying part thereof for transmission to said display means.

Claim 25

The apparatus of claim 17, wherein said illuminating means also comprises: polarizer means for receiving a single, substantially randomly polarized, beam of light from said source and producing therefrom two orthogonally linearly polarized beams; optical retarder means characterized by variable linear birefringence, receiving said linearly polarized beams and converting the same into said two predominantly circularly polarized beams of opposite sense.

Claim 26

An improved method of measuring circular-dichroism, comprising the steps of: simultaneously passing through a sample zone two predominantly circularly polarized light beams of opposite sense; detecting both said beams after passage through said zone and producing first electrical signals in response to said beams; combining and processing said signals to produce a final electrical signal, said combining being carried out to subject any fluctuations of said first electrical signals due to intensity fluctuations which are common to both said beams to at least partial mutual cancellation in the course of said combining; whereby said final signal is substantially freer of effects due to such common intensity fluctuations than are either of saId first signals.

Claim 27

An improved method of measuring circular-dichroism, comprising the steps of: simultaneously passing through a sample zone two predominantly circularly polarized light beams of opposite sense; detecting both said beams after passage through said zone and producing first electrical signals in response to said beams; combining and processing said signals to produce a final electrical signal, said combining being carried out to subject any fluctuations of said first electrical signals due to intensity fluctuations which are common to both said beams to at least partial mutual cancellation in the course of said combining; whereby said final signal is substantially freer of effects due to such common intensity fluctuations than are either of saId first signals.

Claim 28

The method of claim 21, wherein said processing is carried out to cause said final signal to be indicative of the circular-dichroism of any material in said zone.

Claim 29

Apparatus as defined in claim 17 wherein said illuminating means comprises, in sequence, a monochromator to receive light from said source, a polarizer to receive light from the monochromator and to produce two linearly polarized beams polarized mutually orthogonally, and an optical retarder to receive said beams and to convert them into said two predominantly circularly polarized light beams of opposite sense.

Claim 30

Apparatus as defined in claim 17 wherein said illuminating means comprises, in sequence, a monochromator to receive light from said source, and a polarizer to receive light from the monochromator and to produce said two predominantly circularly polarized light beams of opposite sense; said detection and display means including in sequence after said sample zone an optical retarder to receive said light beams after passage through said zone and to produce two elliptically polarized beams, and another polarizer to receive said elliptically polarized beams and produce two plane-polarized beams.

Claim 31

Apparatus as defined in claim 18 wherein said detector means comprises a single phototube to receive said beams in alternating sequence and to produce said two currents in response to said reception.

Claim 32

Apparatus as defined in claim 18 wherein said detector means comprises two phototubes respectively to receive said beams and to produce said two currents.

Claim 33

Apparatus as defined in claim 18, also comprising means for periodically interrupting said beams independently at two different frequencies respectively, wherein said detector means comprises: a single phototube to receive said interrupted beams and to generate a composite electrical signal in response thereto, and frequency-sensitive means for deriving from said composite signal two component signals at said two frequencies, said component signals being said two electrical currents.