DE2324502A1 - POLARIZATION INTERFEROMETER WITH BEAM POLARIZATION AND DECELERATION DEVICE - Google Patents

Description

PATENT LAWYERS. y-> j p ^ - <j Jj

DR. CLAUS REINLÄNDER
DiPL-ING. KLAUS BERNHARDT

D-8MONCHEN60 O O O / r Λ ο

THEODOR-STORM-STRASSÜ 1 «? Z 0 Z 4 U U £

YARIAN Associates »Palo AItO ₉ CaI _es USA

Polarization interferometer ait Strafelpolarisieru ^ gs- and delay device

Priority: May 15, 1972 - USA - Serial Ho, 253 303

The invention relates generally to a device for measuring polarization-dependent optical properties of samples and particularly affects the application of interferometric techniques with associated sampling with such measurements.

Measuring circular dichroism (a very useful optical property of substances and defined as the difference in absorption of an optically active sample when determined using left-hand circularly polarized light and then right-hand circularly polarized light) has included in the past * and as ZeB _{11 is described} in US Pat. No. 3,257,894 "the step of obtaining the ratio of alternating and direct current" components of an electrical signal "obtained as the output signal of a detector" such as a photocell ". The light _p that falls on the detector

309848/0948 _{eso / 2}

the generation of this signal is caused ₉ typically comes from the emission of a beam from a source with a · monochromator and a polarizer by two counter-rotating "circularly polarized components," whereby the relative sizes of the two components change cyclically over time - with a modulation frequency of ⁸⁸ - so that the basic component is alternately right and left = circularly polarized). Before a sample is sent »The latter absorbs, if it is circular dichroic _9, the circularly polarized components of opposite sense and unevenly. periodically changing polarization ^ s © that the total amount of light hitting the photocopies is subject to a corresponding periodic change, CLh ₀₉ wlrd _s i-jeno, the predominant circularly polarized component of the light passing through the sample has the same meaning that is absorbed to a lesser extent by the sample, and less is ₉ when the predominant circularly polarized component has the sense ₉ that is absorbed by the sample to a greater extent o The fluctuating component "of the output signal of the photocell .. izat a © equal to the modulation frequency NND a. AaplJtai proportional to the difference between the BurehlaSpegeXn for the circularly polarized components of opposite sense · _β the Gleichstromkoiaponeate other hand, corresponds to the average or the average transmittance of the sample for light of interest VeilenlSnge.

The above and similar systems require the provision of expensive facilities including Mbziochromators vsaä an electro-optic see Modialators · ■ Although one sieve viel® thoughts made ^a mi the Weglasses, this

sinii the above

309848 / 0-948

Used in existing equipment to measure dichroism in samples, i.e. it is not a viable substitute found

A device for measuring circular dichroism can usually also easily be used for measuring linear dichroism, which is defined as the difference in absorption of a sample for linearly polarized light with the direction of polarization corresponding to the maximum absorption by the sample and a direction perpendicular to that Direction of maximum absorption. Linear dichroism is another useful optical property of substances and is the property on which, for example, the useful properties of thin polarizers such as "" Polaroid "depend. It can be measured with the device described above by introducing a 1/4 wavelength bias voltage ¹¹ into the polarization properties of the light beam by superimposing a sufficient unidirectional potential in the electro-optical modulator in addition to the alternating potential, or by introducing a 1 The light beam passing through the sample then changes cyclically between two orthogonally linearly polarized components of the photocell. impinging light _o

y as should be apparent from the description above the known systems are also limited by the fact that the measurements of a dichroic spectrum are only

3 0 9848/0948

must be performed for a wavelength band and the bands are changed successively by a scanning mechanism in the monochromator = This -is especially in the infrared region of the spectrum troublesome ₉ where due to the very small values of dichroism ₉ that are found usually mentioned _s and because of the downward Property of "constant noise" of conventional photometric display systems _9, a very long time is required for the measurement in each wavelength _{band 9 in} order to collect enough information to enable precise determinations of such small differences in absorption o

At ordinary absorption measurements, it is known for some time _t that are obtained by using the process commonly referred to as "Fourier spectroscopy", and use an interferometer measurements could be carried out simultaneously at many wavelengths "where the wavelength is characterized by a different signal frequency _f which is imposed on the radiation falling on the detector. The signals are then "sorted out" according to the frequency by a mathematical process that is characterized in that the inverse Fourier transform of those signals is taken * which are collected by the detector and By taking measurements at many wavelengths at the same time, it is possible to obtain so accurate or more accurate measurements at each wavelength, ei in the same time with a single wavelength band using a monochromator for wavelength band separation h ätten * can be achieved under the assumption that the detector noise, the same optical bandwidth or resolution s same transmission efficiency and the same "light detection" or like "throughput""

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Another advantage interf erometrischer modulation liagt in the fact ₉ that for a given Ä ^ the means flösungsirsrmögen possible is "melir radiation through an interferometer as through a monochromator to ski & s * This is true for two reasons: The first isG ₈ that the" light detection "d" h _e the geometric factor which determines the ability of the apparatus for transmission of radiation, it was found larger for an interferometer than a monochromator "the second is that the monochromator usually much more optical elements enthältgVon each having a certain loss in The system brings about that the transmission efficiency of the monochromator can be slightly lower, even for a given single wavelength, than for an interferometer, despite the fact that a typical beam splitter in an interferometer reduces the light intensity sent through the interferometer by a factor 2 at the beam re-merging point, since the Half of the radiation returns to the source "

Before the DOS 2 130 974

was no V / eg known, the above interfsrometric Apply cadulation technology to the measurement of circular dichroism. This DOS describes an interference polarization modulator with relative movable reflectors for producing source light and is characterized by negligible production amplitude modulation in the absence of Dichroism in the optical chain that follows the modulator and detector. Both linear and circular dichroism in one area of the instrument

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however converts the polarization modulation into an amplitude modulation _o The polarization modulation is characterized by a different frequency for o ^e & e wavelength of the radiation! characterized the signals ₉ which are caused by the interaction of radiation with the dichroic sample ,, all of which are simultaneously recorded and subsequently separated nztrennung by a simple electronic Freqxe or _S, preferably, by the use of a computer for deriving the inverse Fourier transform * · forming totality of frequencies that form the complete signal »and thereby a transmission spectrum corresponding to the. Dichroism will be preserved *. In the case of circular dichroism, the transmission spectrum, in turn, can be converted into dichroism by dividing it by the ordinary transmission spectrum (corresponding to ordinary absorption), which can be obtained by ordinary Fourier spectroscopy »

Although the DOS _. special polarization interferometer device described has certain unusual advantages, it results in connection with the interferometer device described here additional extraordinary advantages _{or the like}

Summary of the “Invention

It is a primary object of the invention _s for a dichroism measuring device of the type mentioned above one interferometer "arrangement improved design" Generally speaking, includes the arrangement:

a) a source of linearly polarized electromagnetic radiation of different wavelengths Λ ₉

309848/0948 , "

O O O I? l

b) the improved Interferometerancrdnuag for influencing the radiation from the wellspring to provide a beam _s is marked for 3ede wavelength by else ESiptizität which varies between left- and right-circular polarization and between which the beam polarization is linear in a direction If the eu & pticity changes from a left to a right-circular polarization, and becomes linear in another direction if the ehipticity changes from a right to a left-circular polarization ₉ where the characteristic frequency N _a of such a change varies as a function of wavelength ₉

c) for providing a passage for an elliptically polarized beam by a dichroic "sample in the space ₆ in which the sample in different ways absorbs a sample chamber which is provided alternately polarized radiation of a CHARACTERI" stischen group of wavelengths Ä »and

d) arranged a detector for detecting the Strahliiitensität "in the outgoing of the sample space beam path and ₉ characterized in that it provides an output signal which varies in intensity with the frequency N_ _s

al

when the sample is located in said space, wherein the output signal of the processing is angepaBt to produce a dichroic ^ s spectrum wslches with wavelength changes Jl "

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Will be seen ¥ ie ₉ the improved Interferemeteranordnung includes a beam splitter for transmitting and reflecting the light coming from the source light into two beams, beam reflecting and -polarisierende devices in the respective paths of the two beams, wherein at least the reflective means are movable relative to each other, and an actuating device for causing such a relative movement of the devices for controlling del? N. frequencies; · In particular, each of the polarizing means comprise a reflective polarizer or a mirror with a pass polarizer, which is provided to both the _s pass therethrough to the mirror fallenden'als also the reflecting mirror of the beam, or a group of Retroreflective, (reflectors) ·. ^v . · " * . . , "^ , Gates to separate the ray entering the group from the ray leaving the group together with a transit polarizer in the path of this ray, as will be seen"

Optionally, the improved interferometer arrangement may include a beam splitter, as mentioned, beam reflecting devices in the respective paths of the two beams, these devices being movable relative to one another, a beam retarding device in the path of at least one of the two beams and an actuator for effecting such a relative movement of the two mentioned Facilities to control the frequencies N ₀ »The facilities mentioned

CL

may contain mirrors or retroreflectors, and the The beam retarder can consist of a length retarder consist in the path of the beam which is sent twice through the delay device, or from a 1 / & wavelength retarder in the path

309848/0948 _./q

of the beam of _s wirdg only once through the delay means further another 1/2.-wave retarder may be provided and be used as a compensating device in the path of that beam "which is passed through the beam splitter.

These and other features and advantages of the invention as well Details of the illustrated exemplary embodiments can be better understood from the following description and the drawings in which:

Fig. 1 is a representation of the overall system _s

Id perpendicular views are set to those shown in Figure 1 _e beam,

Figo 2 is a diagram for two wavelengths represents the change in polarization as a function of time »

Figure 3 is a waveform * depicting dichroism as a function of wavelength _s .

FIG _o 4 showed a polarization sequence that is characteristic for the invention ,;

Figs 5 shows a polarization sequence, as it is for is characteristic of a conventional electro-optic modulator, and

Figo 6 = 9 representations of parts of the 'system are _? showing other modified forms of the invention "

'309848/0948 «» ../10

«= ■ ru <=»

Detailed description

A light source and a collimator lens are shown in Fig. 1 _S the hatj to do with the measurement of zirkulärem dichroism 10 and 11 is shown, wherein the shaft is provided a broad-band electromagnetic radiation such as _e B _o light under · = schiedlicher wavelengths Z A Aperturblen & e is at 110 »Between the light source and the sample space 12 there is an arrangement that is generally referred to as a polarization interferometer Kaxm _s with beam reflection and polarization controls for influencing the light coming from the source in such a way that a beam is generated at 13» which is characterized for each wavelength by Qine EMpticity which changes between a left and a right circular polarization and between which the beam polarization becomes linear with a direction which is called "parallel" or ^M p ^l! Position changes to a position marked "perpendicular ¹¹ or ⁿ s ^tr " Bisse designation is common and d The frequency N · of this change is a function of the light wave position ₉

where a «is associated with certain wavelengths

standing numbers

N s assigned to certain wavelengths

The frequency of changes in the EQipticity are ",

Figure 2 shows these things _o changes in polarization as a function of time t is for certain. Wavelengths Z «j and Z ₀ tmä. can be generalized for other wavelengths * wea-a is other lines inclination adds the other shaft

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lengths are representative and, of course, are more nulled in the point Ordnimg through the zero axis of the ortic phase goes "Han note that the lines appear to extend indefinitely in both directions and that their range is τοη of velocity and depends on the distance in front of the one to be described moving carriage is traversed, in the interferometer of Fig. 1, the inclination of a line is reversed proportional to the corresponding wavelength »

The sample space 12 is provided to allow the passage through of the beam 13 through e.g. a circular dichroic ^ Effecting sample 14 in the space, wherein, the sample in typically the left * and right idrkular polarized Light of a characteristic wavelength differently absorbed. A detector 15 for determining the beam intensity is located in the path of the beam 13a, which has passed through the sample space 12 »and a condenser or some other optical arrangement 16 may be more known ¥ can also be inserted into the beam path to reduce the size of the beam on the detector, line lens or another optical device 16a can focus the beam 13 onto the sample in the space 12. Another sample space is indicated at 12a, but other places can also be used »The intensity of the output signal of the detector at point 17 is characterized in that it is at frequencies N_ changes when a sample 14 is in the space 12.

The output signal of the detector, an interferogram function F (N _a ), is subsequently further processed by a device, which is generally designated by 18 *, in order to generate a dichroic spectrum which changes with the wavelength Z , as shown in FIG see is ο

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In the absence of a sample, the detector ideally delivers a constant (or direct current) output signal, apart from interfering signals or random fluctuations, The term "ideally" is used because a Detector that is completely free from response linear polarization is very unusual. In practice, benefit is taken from the fact that the circular © dichroism to the signal which from linear. Effects results, out of phase by 90 ° and can therefore in principle be completely separated from the linear behavior in the calculation. In in practice, of course, this separation is never complete, but with careful adjustment and care Structure this can be very useful »

The device 18 shown may include an amplifier, the input of which is connected to receive the detector output signal 17; a digitizing device 20 (such as an analog-to-digital converter) is connected in order to receive the analog output signal 21 of the amplifier and to supply a corresponding digital output signal 22; A digital computer 23 is connected to the digitization unit to generate, as mentioned, a Fourier ⁸ dichroic DurclilaSspektrum Δ ^ j ^ r {X) or Δ T_ _ ( X ), and in conjunction with the equation

p-S µ

A τη nA & v * A fP «■» / 5 T? / ΚΓ \ ν Wf f ji

N
1

derive the demodulation function defined below. A useful computing technique is described on page 1667 of the article "What is the Fast Fourier Transform?", Proceedings of the IEEE, Volume 55, No. 10.

309848/094 8, ._

υ ο ο / I J

A Fourier spectroscopy transmission spectrum T (J2) is derived in the usual way for the usual irradiation of the same sample, and the computer module 23a then divides _{Δτ μβ} {^) or ΔΤ (2 ) by T (by the negative value at the starting point 90 of the approximated absorption spectrum & A _{1 Ώ} (Z) or _Λ , t "" to, received, _t _.,., ^, _. Z \ A _s ( Ji } y which corresponds to the circular bw »linear dichroism, as in Fig Line indicator for linear or circular dichroism is indicated in Fig. 1 at 91. If desired, the output 21a from the digitizer can be recorded by recorder 24 for later computer processing to derive the spectrum T ( X ) would only involve rotating the original polarizer 26 so that its polarization effect is at 45 ° to the direction shown, followed by running the system again and a Calculation of the integral defined above follows. On the other hand, the spectrum T (X) can also be obtained by removing the polarizer alone, which would be preferable when measuring linear dichroism. The interferometer device for generating the beam 13 came to have an associated scanning speed V, which is characterized in that for a selected wavelength λ _ of the light supplied by the source 10 there is an associated frequency N _{a of} the change in the beam hipicity _s as above is described and, for example, _{s can be represented} by the following equation

N ₀ - (

30S848 / Q948 .-. / 14

This equation represents a form _? which may take the equation (1), and the '' work to be described devices generally so _s to satisfy "Dia equation (2), the equation (2) can be regarded as representing the condition ₉ that each wavelength Z ^ the polarization cycle traverses at a characteristic speed. Thus, in FIG. 2, the wavelength Z _{1 runs} through the polarization cycle with a period T ₁ in connection with a frequency M 1, whereas the wavelength X 1 runs through the polarization cycle with a period T ₂ in connection with a frequency H ₂ , wobsi T ₂ iffi generally differs from T 1. Note ₉ that these occur for the same scanning speed V of the reflecting devices which are movable relative to one another in the interferometer arrangement described.,

In FIG. 1, the linear polarizer 26 acts on the light 2 coming from the source. a ₉ to polarize it linearly, e.g. is shown in FIG _o 1a by the vector 28 * A beam splitter is provided to a part of the light beam to reflect 29 and thereby to form the reflected beam and a portion of the beam to allow 29 passing · =, and thus to generate the beam 32 "

A Reflesclons polarizer designated 38 is relative to the reflective polarizer 35 and to the beam splitter JO and also in the positive or negative Y direction and at one speed

309848 / 09.48

V movable, as has been described, for this purpose the reflective polarizer 38 can be on a through an actuator 37 movable carriage are attached. The reflection polarizer (a An example of this is model 186-0240 sold by Polaroid Corporation and used as a reflector) generates a beam 48 which is directed to the beam splitter 30 returns with a characteristic polarization vector, which is oriented in the X direction, as indicated in FIG. 1b by the vector 49. For the sake of clarity, ray 48 is shown as being removed from ray 31; normally however, these rays coincide.

The reflection polarizer 35 acts on the beam 32 a _{9 to} produce a backward course ea · ^ m ΛΖζη with a polarization in the direction d3s vector 43 in the direction of the Z-axis, as shown in Fig «1c» In this relation the polarisais ¹ 35 may be of the same type as the polarizer 38 ₀ The beams 14 and 48 are combined again in the beam splitter 30 in order to generate a beam 13 with an associated polarization modulation ₉ as will be described below in connection with FIG. In this regard, the time coordinate T, as shown in FIG. 2, can be regarded as determining the phase difference <Δ Ρ between the vector 43 and the vector 49 or as corresponding to the movement distance of the actuating device 37. The beams 14 and 48 are separate but coherently linearly polarized beams of approximately equal intensity and have directions of polarization perpendicular to one another; besides, one of these rays is continually delayed in phase with respect to the other,

309848/0948

where the delay rate is different for different wavelengths within the band "

The basic requirement here is not that certain directions exist, but that they are related to one another again combined polarization directions are perpendicular to each other. To be more precise, the separate Rays that are recombined by the interferometer »when viewed independently must be coaxial and their polarization vectors must be in mutually perpendicular directions lie. Although Fig. 1b shows these directions as X and Z, it is not at all necessary that a of these directions is the Z direction and the other is the Y or X direction; however, it is important that the two beams of linearly polarized radiation reunited by the interferometer and which have the polarization vectors described above do not have a resulting component have, which varies significantly in their intensity or amplitude. Otherwise the instrument would respond to ordinary absorption, and this much larger effect would tend to be some to cover up circular dichroism as well as the apparent size of a linear dichroism change. The interferometer described can be adjusted so that there are essentially none Amplitude modulation of the combined beams at 13 is generated.

It should be noted that a carriage 36a for the reflection polarizer 35 in the X direction can be moved at a speed V,

309848/0948 "../17

while the carriage 36 is not moved in the Y = direction. The basic requirement is only a relative movement between the reflection polarizers ₀

The demodulation function K (Jl) mentioned above can be derived by operating the means for determining the position of the moving carriage 36 with regard to the position where the two beam paths are equal, which increases the movement between the beam splitter and the reflector groups 35 and 36 and back ( ie the so-called "zero order" position). Such a device can include two auxiliary light beams, ZoBo contained in the visible range of the spectrum _s . A beam is a broadband beam 80 which emanates from a source 81, is polarized by a polarizer 98 and is inversely related to the above-mentioned beams 31s by the interferometer . 48, 32, 42 and 13 runs, but with the same total optical path length between the split and reunion. After reunification, the resulting beam passes through a polarizer 75 or other strictly linear dichroic device at 82 and is examined at 83, and the resulting signal passes to the computer unit 23b at 84. The interferogram produced by this beam has a single strong peak or an intensity maximum which occurs approximately at the position of the zero order and thus characterizes it and which determines the position of the zero phase of the demodulation function M (x?)

718

309 848/0948

A second beam 85 is a laser beam which is generated at 86 and - preferably rarely has one or several types of axial visual oscillation and is strictly linearly polarized. After passing through the interferometer in the opposite direction to the above-mentioned beams _9, however, with the same optical path length ₉ the recombined resulting beam 87 passes through a polarizer _P labeled 76, although the same dichroic element can be used if so desired ₉ and is examined at 88 and then passes at 89 to the computer unit 23b _s in which a strip counting and measuring system is provided, which enables the determination of the distance traveled by the carriage by counting the strips from the zero order position to be absolutely and precisely determined the computer unit 23b evaluated to determine the demodulation cosine or sine = function M ( Z ), ie to supply cos (N_tj or sin (lTt), which are required for generating the inverse Fourier transform, where cosine or sine in corresponding®! ¥ either a linear or a circular one. Dichroism corresponds to _{9 t} depending on what is to be measured

There are _a Profcen which simultaneously both linear. · 8. "Ch zirkulfiren dichroism show., B'ür would have a complete investigation, the interferogram of such a sample to be processed in the computer zwejnal ₉ once with geder demodulation function _s and one would then the two separate (linear and circular) dichroism spectra of such a sample.The circular dichroism spectrum would show absorption bands that always correspond to some of the wavelength positions for ordinary absorption, whereas the linear dichroism spectrum would not necessarily

309848/0948 BADORlGiNAl.

would correspond to the ordinary absorption spectrum ₈ although it would ordinarily do so. For repetition, the one interferogram carries the information for both the linear and the circular dichroism spectrum.

Figure 4 shows the mode of modulation of the recombined beams at 13 and how they form the repeated cyclic sequence runs through, of which the following list is a complete cycle with an arbitrary starting point

101 - left circularly polarized

102 - elliptically polarized (left)

103 - linearly polarized in the ⁿ p ⁿ direction

104 - elliptically polarized (right)

105 - right circularly polarized

106 - elliptically polarized (right)

107 - linearly polarized in the ^fl s ⁿ direction

108 - elliptically polarized (left) 101 - left circularly polarized etc.

This sequence represents only discrete points in a continuous progression of an elliptical polarization results when two coherent rays of polarized radiation are coaxial and with their polarization vectors oriented perpendicular to each other and the phase of one ray with respect to the other progressively increases.

As is the case with Fourier's absorption spectroscopy As is common, the mirror movement can be either gradual or continuous. Likewise, either

.., / 20 309848/0948

the absolute value of the intensity © of you. Differential can be measured with respect to the path length. The device in Fig 1 _c can werdenβ regarded as an example of a means for generating the polarization sequence described above

An important difference between the polarization sequence of Fig. 4 and those _? by conventional electro-optical modulators (such ZeB ₀ the process described in U.S. Patent 3,257,894) are generated, is ₉ that in the sequence of Figure "4, the linear phases are different at 103 and 107, whereas in the sequence, the is generated by the electro-optic modulator "the linear phases have the same vector direction _o See ζ _β Β- _β the linear phases 103 in the sequence of FIG. 5" How it is generated by a conventional electro-optic modulator ", The latter sequence proceeds cyclically through five of the states shown in FIG. 4 * beginning with the first state 101 or the third state 103 "depending on whether a circular or a linear dichroism is to be measured * It then returns in the opposite direction through the same sequence _p instead to proceed through the states 106 * 107 and 108 as in FIG. 4. The Fourier ⁸ see modulator proceeds through the complete cycle and continuously repeats the Cycle in the original sequence

* It is important that a clear distinction is made between an operation in which: - infrared and operating in the ultraviolet or the visible region of the spectrum <= _t It is known that where the measurements are not random in the infrared range by the

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2324562

Occurrence of photons are limited, but rather by noise that occurs in the detector or the amplifier used with the detector or is caused by the radiation field to which the detector is exposed on all sides, so that the noise per unit of frequency band is essentially independent of the light intensity, the advantage that can be achieved by photographic spectroscopy in the signal-to-noise ratio is much greater than when measurements are carried out with a good photo amplifier. In the latter, the noise is caused by the statistical distribution of the occurrence of photons and thus increases with the total light intensity falling on the detector. In this way, increases with SOtoverstärkem ^ ach additional wavelength band noise is proportional to the square root of the total PhotonenflusseSi, the increase in noise affected the level dersndeieifalls in the signal-to-noise ratio would occur "In other words, although Fourier ⁵ See Dichroismusmessungen benefits in the ultraviolet or the visible range of the spectrum, these advantages do not include the so-called "Fellgett advantage", namely that the time for simultaneously measuring a large number of bands by Fourier spectroscopy is approximately the same as that for measuring one single band is required by conventional spectroscopy, using a monochromator to weed out the desired wavelength band and exclude the other bands e

The modified form of the invention shown in Fig. 6 again comprises elements 10, 26, 11, 30, 16a and 12, as described above; the beam reflecting and polarizing devices but here include mirrors 140 and 141 and, as can be seen, transmission polarizers 142 and 143 »

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22 -. 23245Θ2

The latter are oriented in a corresponding manner by 45 ° raid -> 45 ° to the direction of the linear polarization of the entering beam 29. The polarizer 142 is provided around the beams 31a and 4Sa ₅ which hit the mirror 140 or ₀ from this be reflected ^ hindurclm £ h ssen? the polarizer 143 is provided ^ laundri the rays pass therethrough 32a and 42a, are reflected from the mirror 141 or meet dea * ",. An example ©! one such polarizer is the model labeled HR, a product of Polaroid Corporation. The elements © 35 » 36 and 37 are also the same as in Figo 1 and the beam 13 is the same as described above *,

A preferred ^'R Hach-Zender ⁿ version d @ r Invention ₉ as seen in Figure 7 _e, urafaSt also 1O elements _5, 26, 11, 30, 16a, 12 _t 35' 36 and 37 wi © © b @a described! However, the beam reflectors "- uad" Polaris £ @? <§isn * gauges contain ^ © ^ eils © in® group νοώ retroreflectors, which are provided to tremend the beam entering a group from the beam leaving the group and a DurchlaßpSLarisator in the ¥ @ g of this beam, for example contains the retroreflector group 146 at an angle of 90 ° arranged mirror 146a * aad 146b, ale the beam 31b of the beam Taeb tr © at © n _$ and the retroreflector group 147 includes an angle Mirrors 147a and 147b arranged at 90 °, which separate beam 32b from beam 42b. A common 'Strahlentilur % md reunicator 30 will be wi @ obeastehead and linear pass polarizers 150 and 15' either preferably behind the retroP3fl © kto7gpi @ geln (as shown) or between or y @ v ilmea aageoröaet. The axis of the polarizer 150 is old 0 ° relative to the plane of FIG. 7 (ie _{9 of} the * X ^ RicIittisg) and di ©

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The axis of the polarizer 151 is ^{oriented at 90 v} zn to the plane of 7 (ie the Z direction) »

A principal advantage of the arrangement of FIG ₀ 7 over that of FIG _e 6 is _s that no radiation in the emerging beam which is reflected by the polarizer in Figo is reunited _9, so that the inclination for the generation of non-modulated or amplitude-modulated radiation reduced is.

In both Figures 6 and. 7 the beam 13 is thereby marked = shows that it has an orthogonal direction of polarization, as indicated at 43 and 49 in Fig. 1d »

_S are of the beam splitter Wiedervereiniger 30 exiting beam 155 may su a reference detector recycled οάΘτ in a manner equal to that used for which the beam 13 is used _s d.he for subsequent examination by a sample to be sent and so on ^ This beam is in Fig. 7 as shown extending in a horizontal direction

With regard to the passage of the beam through the sample, the sample for purely circular dichroism shows no difference in absorption for linearly polarized light ρ no matter how it is oriented in the beam. " In the case of linear dichroism exactly occurs Compared = part a = If the sample is oriented exactly in the beam _f shows a difference in absorption for linearly polarized radiation having a direction of linear polarization opposite to that with the fsenkrec to ^ th direction linear polarization. If the sample is purely linear dichroic, it does not show any

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./24

Difference in absorption for the circularly polarized Components «

If the signal for purely linear dichroism is a given wavelength is exactly 90 ° out of phase with the signal for purely circular dichroism these two signals are demodulated independently by the cosine or "sine demodulation function"

The modified forms of the invention shown in FIGS. 8 and 9 also comprise elements 10, 26, 11, 30, 16as 12, 35p 36 and 37, as mentioned above. The beam reflecting devices in FIG. 8 consist of mirrors 160 and 161 and in Fig. 9 of retroreflectors and 163 similar to those at 146 and 147 in Fig. 7o

In each of Figs. 8 and 9, a beam retarder is disposed in the path of at least one of the two beams transmitted through and reflected by beam splitter 30, respectively. The retardation device shown in FIG. 8 consists of a quarter-wave plate 166 in the path of that beam which "passes" the retardation device twice, ie, the beam paths 32c and 42c. The plate 166 is oriented + or -45 ° to the polarization direction of the beam 32ε. The delay device shown in FIG. 9 consists of a half-wave retarder 167 in the path of the beam 31d, which is reflected by the beam splitter 30. The retarder 167 is made as largely achromatic as possible, so that a large spectral range can be covered in Fig. 9 can its axis either at 0 ° or 90 ° to the plane of Fig have. and the axis of the retarder 167 is less than 45 ° to that plane _o A half-wave plate 168 in the path of the can by the

309848/0948

Beam splitter having passed beam are arranged 32d and used as a compensator, d "h _e to compensate for the path length caused by the half-wave plate for its dispersion" It is similar to the lamina 167 is formed, but its axis is parallel or perpendicular to the beam polarization orients ₉ so that it does not create a relative phase lag in the second beam. The adjustment plate 167 provides a phase delay of either the ordinary or the extraordinary beam in the half-wave plate 168 _O If desired, the layers of the retarder 167 and the! Compensators 168 can be interchanged "

The beam splitter in FIGS. 6 to 9 can be made of a thin metal film on a carrier glass plate _9, as is customary, “The retarders 166 to 168 are common devices. The purpose of the arrangements of FIGS. 6-9 is of course to produce a beam 13 with polarization modulation as described above in connection with FIG.

The following were determined from known elements which are useful for certain blocks shown in FIG. 1

Block 15 - Mullard TGS Pyroelectric Detector

(2 mm square), a product of the Mullard Company, Sathampton, England,

Block 19 "Pre-amplifierMoiell 225 t one product

Princeton Applied Research Labs, Princeton, New Jersey.,,

Block 20 - analog-digital computer model AN 271 Pf,

15 bit with "sample and hold ^w * choice _{9? R.} A product of analogy, Wakefield,

Hate.

309848/0948

Block 23 - Computer model 620 / L-105 with 24K memory

620-06 TTY control; TTT (Teletype) Model ASR35; 620 / L-116 priority interrupt module and 620 = 80 buffered input / output = control ₉ products from VARIAN Data Machines, 2722 Michelson Drive, Irvine, CaIo

Block 23a - computer for dividing <ΔΤ ( Jl) by T ( Jl ) |

see block 23, which is used when no data is collected ^ doiu for operated for this purpose in time-division multiplex -jr or a double machine with a smaller one Memory (4K) and without TTYe

Block 23b - Stripe Counter and "Peak Centers" Identi ficer ο See block 23aο

Block 24 * = recorder; see block 23a above _o

Block 91 - display device; Varian Data Machines

Model 620-72 digital chart recorder and control.

309848/0948

Claims (1)

Claims ί Λ J device for measuring dichroism _s characterized by a) a source of electromagnetic radiation with different wavelengths Z , b) an interferometer device for influencing the radiation from the source in order to generate a beam which, for each wavelength, is characterized by an ellipticity which changes between left and right circular polarization and between which the beam polarization becomes linear in one direction when the ellipticity changes from a left to a right circular polarization and becomes linear in the other direction when the ellipticity changes from a right to a left circular polarization, the characteristic frequency N _{& of} this change as a function of the wavelength varies, c) a sample space for creating a passage of the elliptically polarized beam through a dichroic sample in the space, the sample absorbing the alternately polarized radiation of a characteristic group of wavelengths I in different ways, and d) a detector for measuring the beam intensity which is arranged in the path of the beam which emanates from the sample space and is characterized in that it supplies an output signal which changes in its intensity with the frequency N _a , 309848/0948 ■. 23245Θ2 W. if si *, a sample is in the room, the output signal being adapted for subsequent processing to generate dichroic spectra which change with the wavelength Z , characterized in that e) the device contains a beam splitter ₉ to transmit and reflect the light of the source in two beams, that beam reflecting and polarizing devices are provided in the corresponding lying of the two beams, of which at least the reflecting devices are movable relative to one another, and that an actuating device is provided for effecting such a relative movement of the said devices in order to control the frequencies N_ a. ο device according to claim 1, characterized gekennz e ^ ic HNET that said means include a reflective polarizer contained 3ο Device according to claim 1, characterized in that each of the devices contains a mirror and that a transmission polarizer is provided to allow both the beam falling on the mirror and the beam reflected by the mirror to pass through. ο device according to claim 1, characterized in that each of the devices contains a group of retroreflectors for separating the beam entering the group from the beam leaving the group and a polarizer in the path of that beam » 309848/0948 ../A3 2324562 5. Device for measuring dichroism, characterized by a) having a source of electromagnetic radiation. different lengths A. _s b) an interferometer device for influencing the Radiation from the source to create a beam, which is characterized for each wavelength by an ellipticity that extends between left and right circular polarization changes and between which the beam polarization becomes linear in one direction »if the ellipticity of a left-to-right circular polarization changes and becomes linear in the other direction when it changes the ellipticity changes from a right to a left circular polarization, with the characteristic Frequency HL of this change as a function CL the wavelength varies, c) a sample space for creating a passage of the elliptically polarized beam through a dichroic sample in the space, the sample absorbing the alternately polarized radiation of a characteristic group of wavelengths X in different ways, and d) a detector for measuring the beam intensity placed in the path of the beam _? which emanates from the sample space and is characterized in that it supplies an output signal which changes in intensity with the frequency IT, el if there is a sample in the room, where ... / A4 309848/094 8 "2324562 the output signal is adapted for subsequent processing in order to generate the throic spectra / which change with the wavelength Z »characterized in that e) the device includes a beam splitter for transmitting and reflecting the light from the Source in two beams, a beam reflecting device in the corresponding paths of the two Beams, the devices being movable relative to one another, a beam retarding device in the path at least one of the two beams and an actuator for causing one such relative movement of the said devices to control the frequencies N_ » 6. Device according to claim 5, characterized. that each of the facilities contains a mirror 7. Device according to claim 5 » characterized iehnet marked. 3ede that the means comprise a Qruppe of R _e tro * reflektcren for separating the containing of the Qruppe a "passing beam group exiting beam. 8. Device according to claim 5, characterized in that «the beam retarder consists of a quarter-wave retarder in the path of the beam which runs twice through the retarder. 9. Device according to claim 5, characterized. that the beam retarder consists of a half-wave retarder in the path of the beam that once passes through the retarder «, 3 0 9848/094 8 1Oo device according to claim ?, thereby marked ichnet. that the beam reflecting device receiving the beam reflected by the beam splitter contains a reflection polarizer, 11. Device according to claim 8, characterized by a further half-wave delay _? which only works as a compensator in the path of the beam that has passed through the beam splitter » 309848/0948