DE1472095C - Interferometric method and associated interferometer - Google Patents

Description

The invention relates to an interferometric method for examining objects using a point light source and a a beam splitter assigned to a condenser and a beam-combining beam assigned to the objective Element as well as an interferometer to carry out this procedure. The one suggested here Compared to the known devices, interferometer offers the following advantages: Simplicity of construction and the settings, stability of those supplied by the device Interferograms and a wider scope.

Interferometer, the two beam splitters (wave duplicators) are well known - they can be used as an interferometer due to their operation denote by defocusing, such as, for example, the devices from Philpott ("Revue dOptique", 1952, P. 42), Smith (British Patent 639 014) and Dyson ("Revue d'Optique", 1952, p. 35); with these known devices, a light source is used to illuminate the object to be examined, whose interference pattern is observed, the reference wave crossing the object and thereby necessarily causes a disturbance, this brings about a blurred image due to the remaining structure of the reference wave, which can be traced back to it is that defocusing is practically never enough. On the other hand, the image becomes the light source through a bundle of light with large angular oiling, which softens the coherence and the contrast of the contours diminished, depicted on the object. In practice, the use of the interferometer is with defocusing limited to the inspection of objects with a small surface compared to the object field, which show only slight changes in the optical path.

The idea was then that these disadvantages could be eliminated by taking advantage of other advantages on the condition that the reference wave traverses an almost point-like area of the object. This led to the following considerations, which form the basis of the invention and which, with reference to FIG. I of the drawings. Let there be a white light source S with a small diameter but good brightness, a condenser C, which is coupled to a first wave multiplier (which is not shown here for the sake of simplicity), a transparent object A, an observation lens O, which is connected to a second wave duplicator is coupled (which is also not shown here for the sake of simplicity). The object Λ is characterized by the distribution of its optical thickness, namely by the function W (ο, Θ), in polar coordinates ρ and Θ based on its center point. Under these conditions, the condenser C forms an orderly image S ₁ of S, while the wave multiplier, by splitting the wave .T, simultaneously creates an extraordinary image - S _{2 of the} same source.!? gives that z. B. in front of 5Ί and at a distance / from S ₁ is located.

The device which is formed by the condenser and the first duplicator or beam splitter is selected so that the two images S ₁ and S _{2 are formed} by light beams with the same angular aperture u . The object A is brought into coincidence with the secondary source, which is formed by the image. In this case, the wave ₁ , starting from S ₁ , continues its path beyond the object without any deformation: Σ _ι is thus the reference wave here. The wave Σ _2, on the other hand, starting from S ₂ , reaches the object within a circular zone of radius ο = / · tg u = S ₁ Zl ₁ . The observation lens, which is shown in the form of a lens O , forms two new images S ₁ 'and S ₂ ' of S, while the wave duplicator coupled with lens O _{brings the image S 1} 'into the image plane of S ₂ ': the Image S ₂ 'is therefore an orderly image of S ₂ by means of lens O and image S ₁ ' is an extraordinary image that was obtained by interposing the second wave duplicator. In reality, these two coherent, secondary sources are not identical; Image ₁ 'is probably a geometric image of S and S ₁ , but image S ₂ ' is surrounded by a halo, which is the diffraction image of the object and which contains all information about its phase structure. The emerging wave Σι bears the imprint of the object and is characterized by a distribution of the optical path; this distribution W (ο, Θ) is almost the same as that of the object. So you have:

IV (ρ, Θ) = IV (ρ, Θ) cos u _n ,

where cos u _{n is} the slope factor close to / ■, and U _n is linked to 1 / by the equation η sin u _n = sin u, where / ι is the refractive index of the object.

The waves -T ₁ 'and -T ₂ ', _{emitted by S 1} 'and S ₂ ', can interfere in the interior of the space shown on FIG. 1 is shown hatched. The interference image or interferogram of the object z1 can be captured in plane A ' , which represents the normal image of plane A through objective O.

In particular, the image of a point A ₁ on the edge of the field in / I ₁ 'is formed.

The brightness distribution / (ο, Θ) in level A ' is through

2 ?!

I (ο, Θ) = I ± cos - ^ [W (ο, Θ) - / F (0,0)] cosw "

given, where λ is the wavelength, W (ο, Θ) and cos U _{n have} already been defined above and IV (O, 0) is the optical thickness of the object in the center (ß == 0, Q = 0). The sign depends on the type of interference, which can be either white or black in the center.

The formula defines the so-called interferences with a horizontal section that are observed when the images S ₁ 'and S ₂ ' coincide exactly. In the case shown in FIG. 1, the images S ₁ 'and S ₂ ' are slightly shifted laterally, and in this case the interferogram is traversed by parallel stripes.

If you want to visually observe the interference, you will bring the pupil of the eye to the position of the images S ₁ 'and S ₂ '.

Fig. 1 illustrates the interesting fact that the proposed system has the following remarkable properties: On the one hand, the condenser C forms an orderly image of the point source S without a wave duplicator in the object plane A, on the other hand, the image A 'of the object A is formed by the objective O. formed without an associated wave duplicator coming into function.

The invention is based on the object of the interferometric 'method of the aforementioned To improve the manner in such a way that it

guide an interferometer can be used at the assigned point (n, (-)) and the second, in his

which is simpler in its construction, the one-point of which passes through (0,0); these two rays

Positions are easier to make and these are parallel, inclined to the axis around the same

Application area is larger, where the angle »and in the same azimuth plane Θ

Interferograms delivered by such a device hold a higher 5. This clearly shows that the principle of the device

Have stability. according to the invention is essentially different from the known

With such an inter- principle of the interferometer with defocusing, this task is

ferometric method solved in that separates through; at the same time one sees that the physical

the condenser and beam splitter principle of the invention is cleaner, d. H. more clearly defined,

optical system a decent picture of the light source ¹⁰ which brings a better operation with it,

at the location of the object to be examined and in front of The wave duplicators or beam splitters, which with

Extraordinary features of the observation optics or with the condenser, which lie in the orderly image

Image of the light source designed and that are coupled by are, according to the invention, one another

that consisting of objective and beam combiner is identical and must be the same in each case

optical system have a decent picture of the first »5 properties. According to the invention, everyone must

Extraordinary light source image and an additional one of these Duplicators offer the possibility of a

neat image to form the first neat light source additional focus, the one above

image designed in the exit pupil of the lens was called extraordinary focal point and

while the interference image of the object in the from the ordinary. focal point of the lens in a

the image plane of the lens is created. . ²⁰ sufficient distance / separate. Besides that

A device for carrying out this method, the duplicator, must be designed in such a way that an extraordinary beam of rays with the same angle can be designated as an interferometer with a pin-shaped reference. ^; opening like the neat bundle passing through that

It may be of interest in this regard to produce b.eob lens alone. Such beam splitters must ensure that, if one uses optical devices in the arrangement according to FIG they are coupled, or strongly replaced by these lens sources, whose image through the condenser is the blind one. One can, among other things, cover the object to be examined and, if one envisages that either the combination of mirrors takes any point P of the said source, 30 contained in the Sognac interferometers, which can then be his images P ₁ and P ₁ in the object, so-called parallel wave interferometers, in front of or in the plane of the image S ₁ , or devices with double breakers but the two secondary sources then have the prisms as a beam splitter. It is expedient to notice the reverse function of that according to the invention that in certain cases one has been entered, and the wave emanating from P ₁ numerous duplicators or an equivalent. Element then serves as a reference shaft for the starting from P ₁ -can use, which then successively the role of the shaft. The reference wave thus traverses the object of the first and second above-mentioned duplicators and is wildly disturbed, which, thanks to the invention, takes over.

can be avoided. In the case of the extended source the dividers independent of the lenses are in the

one can also observe an interference image that is generally set in the object space, i.e. H. between

the plane of the exit pupil S ₁ , S ₁ 'of the device the condenser and the object or between the

of the invention is formed; this interference pattern is the object and the lens. The dividers fall with theirs

From a geometrical point of view, even the extraordinary image focusses apart and are optically

of the object A in the objective O, which is formed by the sub-elements with flat surfaces. Self-

This type of divider can also be used in the

the foregoing shows that the. Image space can be set on the condition that

According to the invention, interferometry does not depend on whether the device which assigns the object to the image

projects with small variations of the optical path, from a system of lenses with different

is limited, with the exception of what the small reference point, which is the focal point, is made up of.

area S ₁ in the center of the object concerns where the 50 In the drawing are duplicates according to the

optical thickness must remain constant. "Invention chosen in various examples

You can see, by the way, that the distance /, the embodiments and applications are schematic

neat image separates from extraordinary, illustrated at. Show it

the invention does not play the role of a defocusing F i g. 2 to 5 different embodiments with

plays; this distance /. is a parameter of 55 mirror duplicators,

Device, which one depends on the opening u of the F i g. 6 and 7 doubles from birefringent

Illumination beam path and the radius ο of the material,

Object field selects :. F i g. 8 an example of an afocal optical

Element with spherical semi-reflective upper

/ ₌ - _.ϊ— _ 6o areas,

^: 'g "F i g. 9' to 12 different applications below

Use of reflective surfaces,

The operation of the interferometer with point F i g. 13 shows a structure with a birefringent

shaped reference according to the invention can incidentally prism as a beam splitter and '

can also be explained by noting that the 65 F i g. 14 the application of an afocal system

Intensity E (ρ, θ) at any point (ρ, Θ) between the object and the afocal duplicator.

Interference pattern from the interference of the two. In the case of FIG. 2, the first duplicator is D ₁

Rays originates from which the first .the object of two plane mirrors / H ₁ and wi _a and the second

Duplicator D _{2 formed} by mirrors m ₃ and / M ₄ ; the distances between the two pairs of spicels are the same. A first image S _{1 of} the source S is thereby obtained through the bundle of rays which directly penetrates the duplicator D ₁ (/? /, And; / ;,) and which supplies the reference waves. The second image S _{2 of} the source S is formed at a distance / - S ₁ S ₂ , which corresponds to twice the space / M ₁ , / H ₂ calculated in air. It can be seen that the axial distance / does not depend either on the lens C or on the position of the mirrors / M ₁ and / M ₂ with respect to the object.

The second splitter D ₂ (mirror / M ₃ , / M ₄ ) allows the two beams shown to be combined again, one of which passes the center point and the other the point A ₁ at the edge of the field of view. The two bundles then form a common focal point in S ₁ ', S _t', where the Austritlspupillc of the interferometer is located, and it is observed in the A ₁ lnterfercn / image of the object point _A1.

The two pairs of spicels are preferably formed from two identical glass plates, which are semicircular Layers \ are seen.

In order to adjust the number of strips, one of the plates can advantageously be tilted slightly, which results in a slight shifting of the image S ₁ and thus a lateral shift of the images S ₁ and S ₂ . ■

The thickness of each plate is determined as follows as a function of the object field and the angular opening w _{r of the bundle of collars.} One goes from

"* i /
the formulas η - S ₁ A ₁ ■ - / -te η and " - η ,

where μ is the index of refraction of the plate under consideration.

It is of interest to get to know the value of the translucent wedge of the arrangement. To do this, one determines the reflection coefficient R of the mirrors »; ,, / M ₂ . / M ₃ and / M ₄ . which ensures the greatest brightness for this device. The amplitudes U ₁ and C _{2 of} the two waves of the interferometer are accordingly:

I ₁ T ₂

where / and τ are the torn and reflected amplitudes of the mirrors Hi ₁ to / M ₄ , which are assumed to be identical in the present case. As is well known, the permeability of an interferometer is defined by the intensity /. «. Of the white interference stripes:

T =) - = - 4T ¹ R- = 4 T * (IT) "-,

where 7 '- / -' and R --- r ^{2 are} the reflection coefficients of the mirrors used> ind.

The derived function '. *' Of the above

U /

Intensity I'm equal to zero for the maximum value of the permeability T, which corresponds to the best value of R:

UT

(Im) = 4 Γ »- 10 Γ« - 6 Γ ⁵ = 0,

This results in a maximum intensity In or [ the maximum permeability of the interferometer according to the invention to: I.

- 9

what T - ^; , ₃ and therefore R = ¹ Z ₃ results.

This shows the importance of the selection of the reflection coefficient R of the mirrors; if instead of R = ¹ J ₃ z. B. R ~ ¹ J _{2 is} used

ίο you get a maximum permeability /.!/ ~ 6%.

. The quality of the transmission of an interferometer of the Tv ps described here can be improved considerably and in a simple manner. For this purpose (FIG. 3) the pair of mirrors Di ₁ Di _{2 is positioned in} such a way that the image S _{2 of} the source S is formed on the mirror Di ₁ : the partially transparent surface is replaced by an opaque, reflective coating from a reflection R ₁ - 1, and the extent of the covering is restricted to that of image S ₂ of source 5

ao occupied area. The correction coefficients of the mirrors made of dielectric material zm ₂ , zm ₃ and Hi ₄ are then calculated with the help of a calculation such as those used for the example in FIGS. 2, determine and provide the maximum intensity of the white stripes of the interferometer. This calculation shows that the maximum permeability wedge / .u with the reflection coefficient R ₁ = 1, R ₁ = 0.19 and

R ₃ = A ' ₄ - 0.43 reaches the amount of 19% ".

The structure of Fi g. 2 can be changed to allow examination of reflective surfaces. Starting from the device of FIG. 2. If the straight line S ₁ A _{1 is} folded around the object, it has been possible to develop a device which is shown schematically in FIG. 4 and which allows the examination of reflective surfaces.

The mirrors; m, and Dl ₁ are separated by the distance /, and the incident ray ν is introduced into the device by a semi-transparent mirror M

.40 steers. To eliminate the stray light due to the direct reflection (indicated by arrows 1 and 2) of the beam falling _{on the mirrors / M 1} and / M _2. were crossed polarizers .I ₁ andrr ₂

cinccsctzt while a _; '-Ticker between ob-

■ ~ 4

jckt A and the mirror Di ₂ switched the way for the light that is involved in the interference.

However, this very simple apparatus offers up

Due to the additional optical elements, only a brightness that is approximately eight times weaker than that of an interferometer according to the Lligation and that works in transmitted light. If the illuminating mirror M is omitted and the source S itself is placed in the center. _{-I 0} 'of the image plane', one can obtain a brightness factor which is only four times weaker . ■. ■

Despite their relatively weak brightness, they are suitable the devices described here for microscopy with medium and high magnifications, where there is little space for the optical elements in between remains in front of the object and the condenser. The method of the invention can also be practiced be'with duplicators or dividers with inclined reflective surfaces that increase the number of Minimize the passage of the semi-transparent mirrors. This variant that the possibility offers a higher maximum permeability, is particularly beneficial for microscopes with weak

Magnification, or more generally speaking, when it is used to visualize objects; you will

so-called macroscopic object: goes. note, however, that in this case the above

A first device suitable for this purpose, which does not occur in said disturbing wave a _{t and that the} Fig. 5a is shown is limited to the radio additional polarization devices, not necessary

tion in incident light. This device contains two semi-5 manoeuvrable ones. ·

transmissive mirrors / M ₁ and / M ₂ as well as a deflection in general can be any structure with inclined

mirror with the: lighting lens C projects a mirror, at least one of which is partially transparent

Image Si of the almost punctiform source 5 is in the middle and the unfolded the scheme of Fig.l

point of the ^: reflective object A, while an equals, for applications according to the invention

second image S _{2 of the} same source S is formed in S ₂ , io can be used.

at a distance / = / M ₁ ZMm ₂ - Tn ₁ Tn ₂ . The ob- Figures 6 and 7 show wave duplicators that

jektivO, whose object-side focal point are independent of that of the lenses and the double

Object collapses, allows observation to use refractive material,

of interferences under the condition that the duplicator in Fig.6 consists of a plan-

Pupil on the coincident images S ₁ ', S ₂ 15 parallel late platelets D, which are parallel to the object ^

from S ₁ andIS ₄ . The process is the same as that of,. that is assumed to be reflective. the

which was described with reference to FIG. optical axis of the crystal is perpendicular to the op-

The amplitudes of the two waves are: table axis of the interferometer .; The neat one

_s bundle (a single ray that is fully extended

^fl i ^{= r} i ^r 2 ^r « ^r i ^{= r} * ' ao is set) forms the center of the object Λ that

ej = T ₁ r _s / ₂ Z ₁ "= ^: r < ^a . ■ Bi'd ^ i of the ⁿ ^ ¹ shown point source S.

The extraordinary bundle (shown in dashed lines)

The maximum intensity is: (a _t + ^ ₁ ) * = r ^t t ^l - RT. forms a virtual image S ₂ . The refractive index / 1

The optimal value in the size of 0.25 is obtained from the surrounding medium being equal to the orderly

with R = T = 0.5; ■ it is to be noted that the as borrowed refractive index / I _{0 of} the Spat is assumed,

two reflections of the first ray two over- The usable area of radius ρ is determined by the

corresponding to the second ray. Known - already mentioned formula '; / ■.: [■■ ,'

borrowed, the phase difference of the two waves is then η == SA = I'tau >ί;>;'· ■ (

equal to π on condition that the divisors / M ₁ and m, * ^x

have no absorbent properties. The Inter 30 determines, where / is the distance that 'according to the

reference strip, which gives a difference in the optical path axis the ordinary picture of the extraordinary,

equals zero, so it is black and achro- picture separates:

automatically, which is beneficial. . _ Δη. ^,

In Fig. 5a one can see two crossed polar _o n _e

sators ^ and ^ as well as a - * - plate between ³⁵ _{where Πο the ordinary and} : ", the extraordinary

the mirror / w, and m _{t is} set. These polarizers are the refractive index of the spate. The device

and the _ -plate allow interfering waves also holds the ^ -plate, which is between the object

to switch off the amplitude a ₄ , which is the only 40 and late platelets and below 45 ° compared to the

can be disturbing. Except for the rays, the image plane is aligned, as well as two not shown

interfere, polarizers. The - plate guarantees the

_and ■. · ■ ■■ _ ^r ~ ^x * * ^x . ■. Compensation of the optical paths by reducing the polar

"_,"., 45 sation level for the rays that pass through it twice

a ₂ -I ₁ ^ Uh, traverse, turns 90 ^.

There are two other undesirable rays: Such a device for investigation

_ 'of transparent objects contains two identical

ft-'i'i'i'i, · late platelets between which the examined object

^a * = hr _t r ₂ r _± . ⁵ ° and a ^ plate are arranged.

The beam is not dangerous as it always has the. The transmission factor of all interferometers The center of the image happens, while the second according to the invention will in principle be at 25%, Ray a ₄ gives a blurred image, which occurs when it contains birefringent elements,

superimposed on the interference pattern. This disturbing wave 55 In addition, the device could be designed so

with the amplitude σ «is crossed through that one has a focusing effect on a part

Polarizers π, and π ₂ and, for example, that of the bundle that contains the duplicators according to the

~ Tokens switched off. Finding traversed, you practice a first case, like

^z he in Fig. 7a, 7b and 7c is shown, there are

Fig. 5b shows a particularly advantageous 60 different ways of realizing a

management form of this device, in this case such device. In the case of Fi g. 7 a

the dividers / M ₁ and m _t by the two on top of each other holds the interferometer according to the invention one

perpendicular faces of an isosceles birefringent lens L, which is the illuminating or

90 "prism is formed, which is assigned to the observation lens O with another identical.

like prism is glued together and that with 65 The lens L consists of a plano-convex lens L ₁

Total reflection works. The interferometer, which according to FIG. 5b is made up of spar and a plano-concave lens L ₁ made of glass, can by means of an interferometer with an identical refractive index n, which is the ordinary

Duplicators for the investigation of the refractive index m | j of the spate is equal. The neat

■ ..- '»009i45 / 48

9. 10

lent focal length of the lens L is infinite, and its In Fig. 8 a you can see a glass plate M ₂ and a

extraordinary focal length is equal to f _B glass meniscus M ₁ , which is partially transparent or partially reflective

. animal (Ot ₁ and W ₂ ). In the present

f _B - , the device corresponds to a divergent case

At 5 lens with a focal length half the radius

the spherical, reflective surface Hi ₁ with B the radius of curvature and Λ η the double-speaking,
refraction is: This element has the same task as the

birefringent lens described above.

An = / J ₀ - n _e = 0.17 for Spat. io This device has a strong focus

Effect, but it has the disadvantage of being weak

c-. Jo · u .. * ■ in ··., U ·. · Brightness. The permeability of an interferometer

A, plate aligned at 45 is between .. ", _cc ^{,, 6} .... ,. ..,,

.4 according to the invention that with such bifocal

see the lens L and which is equipped here as reflective elements, is incidentally with that of the

taken object A arranged. »5 interferometers with four planar, partially transparent

The light coming from the source S becomes identical by mirroring, which has already been described above

TT _{1 is} polarized and with the help of the semi-transparent (Fig. 2). The best value of its reflection coefficient

Mirror M sent to the object A. That of the zient is also equal to ¹ J ₃ . Object A reflected beam passes through the mirror M, the embodiment of Fig. 8b relates to a

and after passing through the polarizer π., analyzes 2 ° bifocal element that allows the focusing

it reaches the image plane A ', which effects the object A to localize outside the two mirrors,

through the objective O considered here alone. As used in the case of a birefringent lens

is ordered. we have two concentric surfaces W ₁ and w ₂ ,

The mode of action of the birefringent lens L, its effect on the twice reflected beam

which is assigned to the objective O is shown in FIG. 7b 25 is the same as that of a lens which in common

of course. This lens is located in the image center of curvature C of the mirrors Ot ₁ and Ot ₃

side η focal plane of the lens mount ?; in this case is arranged. .. ·. ·. ·; · '. ^:

the refractive power of the two lenses O and L is not

changed. The ordinary beam gives picture ₁ special for the investigation of reflective

the source S and the extraordinary ray the 3 ° surfaces, except for the device of Fig. 1, which

Picture ₂ ; both rays have the same opening u _c . with its four partially transparent mirrors rather for them

The marginal ray of the extraordinary wave is suitable for examining transparent objects

illuminates point A ₁ , which is at a distance ρ. The reason for this is that the two wave

from the center S ₁ is located. duplicators that work with the condenser or the

.35 lens are coupled by a single element

ρ = h J-- , are formed when there is reflected light

/ b acts, and that auto-compensation through auto-

collimation is present, while the two wave

where / is the focal length of the lens 0 and h is the duplicator for transparent objects material

The pupil height is: 4 ° separated and this is a fraction of the wave

h = f sinu length must be made exactly optically identical.

To study transparent objects

what results: to simplify, there is another property of the

__ / ² . 'Interferometer according to the invention in that a

^ ~ ~ r ~ " ^e '45 auto-compensated duplicator is used as

it is shown in Fig. 9a as an example. In this

In the _{1 case of} fig. 7c is the optical figure, you can find all the important components

Center of the birefringent lens outside. an interferometer with a point reference with

Such a lens can therefore rather be fitted with a micro-afocal wave duplicator, which is in the space that

scope lens, the focal plane of which is 5 ' the illuminating lens from the observation lens'

is not accessible. separates, are set.

The lens /, consists of a meniscus M from S is a point light source from which the

Glass, the spherical surfaces of which are both concentric condenser C an image S ₁ in the center of the through-

are opposite the center point C ; on this thick visual object A, which immediately after the half-

Meniscus are two lenses made up of spatulas L ' and L " - a transmissive mirror m is located; forms a second

sticks; the whole forms a plate with plane-parallel image S _{2 of} the source S arises on the axis of through

Surfaces. The image of the center C in the plane w reflected bundle. The two bundles of light

The surface of the plano-convex lens is located in C ₁ , are in the opposite sense by two un-.

and everything is just as if the lens were at C ₁ . translucent mirror M ₁ and Af ₂ reflected so that

The devices with birefringent lenses 60 the light reflected by the mirror m on the right

are easy to use in microscopes that are turned around and the light allowed through is turned around the left

Autocollimation work; They are somewhat more difficult to steer inside the triangle ot, Λ / _{1 (} Λ / ₂ (see arrows)

is in microscopes, for objects transparent to comparable ■. The two coherent waves produced by the

turn as it is difficult to start from the two separate secondary sources S ₁ and S ₂

To make lenses identical. 65 the same mirror ot combined again and can

In the case of FIGS. 8a and 8b, a bifocal will escape in the direction of the objective O , its

optical element used what with the help of spherical. object-side focal point with the object plane ".zu- ■

Rischen, semi-reflective surfaces is achieved. collapses. The merging images JfJ *

11 12

and S ₂ 'of the sources S ₁ and S ₂ determine the exit direction can easily be carried out, whereby one

pupil of the interferometer. Fig. 9b arises by choosing the best direction. The real permeability

Unfold the picture of FIG. 9a. The efficiency of this interferometer is therefore equal to 50% with one

wise this device is in detail on hand crystal polarizer.

Fig. 9b explains. The two light beams are represented by 5. For the study of reflective surfaces of a single beam of the angular aperture u _c , it is advantageous to use the structure of FIG. 11 which is doubled by the mirror m. For those who * deviate from the structure of Fig. 9 in the transmitted beam (solid line), the position of the reflection mirrors AZ ₁ and A / ₂ , the object is in A, while for the reflected one, the one here is so arranged, are that the object A almost ray (dashed line) the object cannot be observed perpendicularly in A, io. 'but in (A) symmetrical to A with respect to the It is clear that the devices of Figs. 8, 10 is point M ₀ , which is in the middle of the line and 11 is not for microscopic examinations in, M ₁ , M ₂ , m . The processes are the same, suitable because the objective O is separated from the object by an inclined mirror m as if the two rays were taking the same path, which means that it crossed the same object at its center or that of a microscope with a weak power in a lateral point A ₁ . The radius ρ of the object magnification decreases.

Field is approximately of The invention can be used with the last described

"_ / * ■ *", "" 1, -:; _ ο e 1 /: _ct embodiments with a microscope with strong

ρ-itguc, where / - ^ ₁ Af ₀ ISt, enlargement can be realized.

given. * ° Fig. 12 shows such an example schematically. In

The structure of the mirrors m, M ₁ , M ₂ corresponds to one in this case, the mirrors m, M ₁ and M _{2 are} as in FIG

Arrangement of S ο g η ac, but here it becomes completely F i g. 9a arranged, but the lenses O and C are

applied differently than with him. The object A must be switched into the circle here instead of outside

as far as possible from M ₀ to be located. Assuming that

or very close to im; on the other hand is a lens C, 25 the refractive power of lenses O and C is identical, so

the real image S _{1 of} a point source S is arranged symmetrically to the center M ₀ ,

projected, indispensable. Under these conditions to "observe the interference. If S: a

If the objective O, which is a magnifying glass, is the point source of light, then the objective O forms

Observation of a completely defined interference - of which a picture _x , and the condenser C - enters

image and not an image, 'that of the over- 3 ° Image S ₂ again, where S ₁ and S ₂ by a distance /

Storage of the two shifted or inverted are separate. The radius ο of the (field of view from

Images originate, as is the case with interferometers, from the object located at the point of image S ₁ ,

Type Sognac is the case. is then so

In the context of the present invention, the ρ - ltgu _c , ". '■.' ■

Any number of deflecting mirrors, such as M ₁ and M _2, 35. ■

and in no way changes the mode of operation of an inter- whereby u _{c represents} the opening of the light beam.

ferometers according to the invention. The device can put on. '

different ways are realized, for what in practice the absolute identity of the lenses is O

Figures 10, 10a, 10b and 10c show some examples and C is not absolutely necessary. It is enough if

given are. 40 the composite system produced by the lenses O

The device of Fig. 10 includes a divider and C is formed, with the center M ₀ in

group £ and a reflecting prism M. The semi-coincidence is brought about.

translucent mirror in is on an inner putty surface With the same goal you can also create a double

of the splitter ". The object A is very close to m Use the refractive prism as a beam splitter,

arranged. The setting of the number of strips 45 in such a case is the angular split

and their orientation is generally very weak in the well-known manner of the rays, which

with a diasparometer K. requires special measures, which in turn require a

In the embodiment of FIGS. 10a, this entails a great structural length. The device

Reflection prism M ₁ , a triad with three on top of each other from F i g. 13 contains a birefringent prism Q,

perpendicular faces the roof of the Inter- 50 X _{p "hn rechtwink} i _{ig gekre} polarity uzte

makes ierometer unadjustable with regard to the angle. 4 '

In Fig. 10b, the prism M _{1 is} replaced by a lens O ₁ sätoren Jt ₁ and π ₂ and the semitransparent mirror M, which is combined with a plane mirror M, which lies in the focal point of the prism with reference to the objective point of the lens O ₁ is. system O ₁ , O _{2 is} assigned, which is afocal and a

In Fig. 10c the divider group E ₁ consists of a 55 magnification g = .- 1 has; the object A is in

Pair of prisms / j and P ₁ with angles of 30 and 60 °; touch with the objective O ₂ . That of a point

The prisms are light emitted through a partially transparent surface m- shaped light source

separated. a semi-transparent mirror M on a double

The brightness of the interferometer with point-shaped refractive prism Q is directed; the middle ray will

Reference for which an arrangement is used that is ⁶ ° in two by an angle. 2 «separate beams

to the Sognac interferometer or a wall. Due to the properties that the

ment, remembered, is most strongly compared to the overall device given, go through the

with those given by the invention. two mutually perpendicular polarized waves which theoretically equals 1; In practice, it is an arrangement in the opposite direction, but similarly advantageous, to use a polarizer (π of FIG. 10) 65 to what is preset in the one shown in FIG. 9, the plane of vibration of which happens perpendicular to the direction. The intersection of the bundle image plane lies. The coherent division of the wave on is avoided by doubling 2x the mirror in can only for a single vibration and the focal length of the objectives O ₁ and O ₂ below

Consideration of the object field selects. For example, in the illustrated case, the source S is arranged at a distance which is twice as great as the focal length of the objective O ₁ . This objective reproduces an image S ₁ from the source S which is at a distance from the objective O ₁ which is twice as long as the focal length / of the objective O ₁ and which coincides with the objective O ₂ ; it images in the center of the object A and covers only the left part (in the drawing) of the objective O ₂ ; this is achieved by giving 2x (the deflection given by the prism Q ) a value resulting from the formula Q ₁ - χ /; »Is the radius of the object field. A second image S _{2 of} the source is formed on the symmetrical part of O ₂ ■ that is not obscured by the object.

The images S _{1 of} the image S ₁ and S ₂ 'of the image S ₂ overlap in the image space, and the real image of the object interferences is then at the point A' which is symmetrical to the source S with respect to the mirror · Λ /

pictured. The, plate that is placed under the prism Q

is set, is necessary in the case under consideration, where the prism Q is imaged on itself with a magnification equal to -rl.

In Fig. 13a and 13b, where the (dotted) line represents the ray divisions, two can be seen Possibilities of birefringent prisms which are suitable for the application which is shown in FIG are; it does not come into consideration here, the prism of Wo 11 as t ο η despite its simplicity to use because the area on which the strips are located and on which the light beam is also located is split, is inclined.

This disadvantage is avoided with the structure of FIG. 13a. which contains two crystal prisms Q ' and Q " with crossed axes, which are completed by two prisms Q ₁ and Q ₂ made of glass having a refractive index π equal to the average refractive index of the crystal used. The crystal prisms used have an angle y and the Glass-

prisms an angle; .

The structure shown in FIG. 13b with three crystal prisms Q ₃ . Q ₁ . Q $ with crossed axes \ expire; the outer prisms (λ, and (J ₅ have an angle y and the middle prism Q _t an angle 2; ·. The angle split χ is given by the formula .x ^. I / 1 tg y in the case of FIG. 13a and by χ ~ 2 I / 1 te y in the case of Fig. 13b.

If it is an optical device such as B. a microscope, where the space between the object and lens is too small. In order to be able to arrange an afocal duplicator there, one can see the structure of FIG. 14, which is such a wave duplicator of the afocal type according to the invention. In this case there are four inclined mirrors Λ / ,; Λ /., (Deflection mirror) and / H ₁ . / H ₂ (semi-transparent mirror) again, between the objective O ₁ and the real image.! ' of the object.- !, which is assumed to be reflective, are switched and which is observed through the eyepiece o _c; The objective O of the microscope forms an afocal system with the additional objective O ₁ . The light source S is point-shaped and is projected symmetrically into the center of the image _{by the mirror / H 1.} L liter these conditions the real 'image ^ 4' of the object A is formed in the image-side focal point of the objective O ₁ , and the space that is (in the drawing) to the right of O ₁ has the same properties as the space that is in front of the object A itself, except for the ray aperture u that passes through. .

sin lh =

sin U g

with g =

/1.

is given, where / is the focal length of the lens O ₁ and / is the focal length of the lens O. The point source S thus allows the interference pattern of the surface A to be observed in A '. The radius ρ »5 of the area of the interference image is given by η = / tg« _c ', where / is determined by / ' --- 2 w ,, Λ / _ο - / h " m, and where the angle u _c ' from the n-umeric aperture μ, · of the objective by the equation

. Sin ur

sin Uc

/1

^ ZZ £ 7

is dependent.

In the construction of FIG. 14 you have a practical means of using an interference microscope for reflective objects, in which the internal structure is on the side of the eyepiece is arranged and in which the lenses can be easily exchanged. Of course the wave duplicator given here as an example can be replaced by any afocal model be replaced. .

Claims (8)

Patent claims: 1. Interferometric method for examining objects using a point light source as well as a beam splitter assigned to a condenser and a Radiation-cleaning element assigned to the objective, characterized in that that the optical system consisting of a condenser and a beam splitter creates a neat picture the light source at the location of the object to be examined and an image lying in front of the orderly image extraordinary image of the light source and that through the lens and beam combiner · existing optical system a decent picture of the first extraordinary light source picture and an extraordinary picture of the first orderly light source image in the exit pupil of the lens are designed, while the interference image of the object arises in the image plane 'of the lens. 2. Interferometer for performing the method according to claim 1, characterized in that that the beam splitters are identical or at least identical to one another in a manner known per se Possess properties. 3. Interferometer according to claim 2, characterized in that the beam splitter with their Mode of action of the properties of the lenses assigned to them are independent. 4. Interferometer according to claim 2 or 3, _as: characterized by that the, beam splitters are closely related in their mode of action with the ■ associated lenses. ., · /,; ..., 5. Interferometer after one; of claims 2 to 4, characterized in that the beam splitter combined mirrors as in interferometers with anti-parallel waves are. . 6. Interferometer according to one of claims 2 to 5, characterized in that the beam splitter consist in a manner known per se from a structure of birefringent prisms. 7. Interferometer according to one of claims 2 to 6, characterized in that a single one The beam splitter successively takes over the function of the element assigned to the capacitor. 8. Interferometer according to one of claims 2 to 7, characterized in that each beam splitter contains a number of partially transparent mirrors. For this purpose 4 sheets of drawings 009 645/48