DE2016529C - Method of measuring the unevenness of the surface of an object - Google Patents

Description

A point image 8 is focused in the focal plane 4 of the objective 3 with the aid of the light beam 7 reflected on the mirror H. The point image 8 can be spaced sufficiently from the point image group 6 by tilting the reflecting mirror 9 accordingly.

A dry plate 10 (hologram) is placed in an area where the light beam 5 and 7 overlay spatially, and is exposed. After the development, the hologram is put back into the brought the same position and now illuminated by the light beam7 alone. Then it will be known the light beam 5 recovered according to the principle of holography, so that the point image group 6 can get. '

If the air wedge is rotated as a whole by an angle Φ , the point spread group 6 of the light beam 5 is shifted by 2 / Φ. By suitable selection of the angle Φ , the / n-th point spread can be brought completely into agreement with the recovered η-th point spread. Here, m and η are positive integers and mean the number of reflections between objects 1 and 2. That is, if the hologram is illuminated with the lens information changed by the rotation Φ as, the reconstruction results in the difference information, which means that the imperfections of the entire measuring system fall out. Other images other than these two, consisting of the / η-th point image and the recovered n-point image, are shielded by the slit 11 at the focal plane. When the wedge is observed, the interference fringes can be seen. The image of the interference tires indicates the contours of the unevenness between the flat surfaces 1 and 2, the difference between the raised and the depressed part of the surfaces, which is given by adjacent strips, through

where λ is the wavelength of the light used.

In the embodiment according to F1 g. 1 it is impossible to increase the visibility of the interference fringes by increasing the intensity of both light rays, that interfere with each other is made equal.

This is done with the embodiment according to FIG. 2 reached. In one of the two optical paths a half-wave plate 12 is inserted when the image is retrieved so that the plane of vibration of the light rotated 90 'relative to the plane of the other light will. A polarizer 13 is used in the optical system to observe the interference fringes. It is rotated so that the interference fringes are observed with a high degree of visibility be able. If the surface 1 has a completely flat reference surface, it can be replaced by a Object to be replaced, the surface of which is to be measured, so that the objects with the reference surface can be compared without the objects in contact with the Reference surface come.

1 sheet of drawings

Claims (1)

2016 52S 1 2 I960 S 304 and 305 interferometers shown Claim: according to Fabry-Perot. It uses a reference and a test beam whose path over the Method for measuring the roughness of the fender object is in progress. When overlaying The surface of an object using 5 reference * md test beam creates an interference image. tion of the Fizeau interferometer, in which the methods described for testing a between the surface to be tested and the surface have the disadvantage that a completely flat an opposing reference surface requires a reference plane that cannot be produced. weak air wedge is and the interference The invention is therefore based on the object Stripes are measured, which are applied to the io a method of the type mentioned above to the sheep test area and the reference surface reflected fen, by which the accuracy of the measurement of Light rays are formed, thereby surface unevenness compared to the herkornmk e η η ζ e i c h η e t that is significantly improved by direct lighting borrowed interferometers th of the two opposite surfaces. This is achieved according to the invention in that a group of point images (6) of the multiple υ by directly illuminating the two opposite reflection of the light beam (5) on the two lying surfaces a group of radio images <i Wedge surfaces (1, 2) on the focal plane (4) of one of the multiple reflections of the light beam to the Objective (3) is focused that through one of two wedge surfaces on the focal plane of an object optical path (7, 9) traversing tivs is focused that through a second Light beam (7) a point image (8) on the ao optical path traversing light beam Focal plane of the lens is focused, which point image on the focal plane of the lens focus ches of a selected point spread that is sated, which of a selected point spreadsheet group (6) a certain spatial image of the point spread group a certain spatial Has a distance that then in the beam path has the distance that then in the beam path of two superimposed light beam bundles (5, 7) one »5 two superimposed light beam bundles a HoIo hologram plate (10) inserted, exposed and gram plate inserted, exposed and developed is developed and then in the same position and then in the same position from Location of the light beam (7) illuminated alone light beam is illuminated altein, so that is, so that the point image group (6) again the point image group is obtained, and that is obtained, and that by slight twisting by slight twisting of the two upper turning the wedge enclosed by both surfaces (1, 2) excludes the two Keiles brought the two selected point spreadsheets into agreement Point spreads are matched. will. By the measures according to the invention 35 achieved the advantage that as a result of the use of Holography the sensitivity of the measurement process is improved many times over the conventional interferometric method, so that also very precisely polished surfaces with very little The invention relates to a method for measuring 40 ger unevenness can be measured. Besides that the unevenness of the surface of an object can cause errors in the optical system of the measuring using the Fizeau interferometer, do not adversely affect the measurement result, in which there is between the surface to be tested. and an opposite reference surface, an example of a management described on the basis of the drawing, weak air wedge is located and the interference 45 It shows strips are measured, which by the at the F i g. 1 is a schematic view of a first Test surface and the reference surface reflected light embodiment of the invention and rays are formed. F i g. Figure 2 is a schematic view of a second As in "Optik in der Längenmeßtechnik", 1966, execution designed to improve visibility P. 253 ff. Is shown, when 5 ° is present, the interference fringe is used. Light interference fringes, if a completely plane It should be the opposite planes Glass plate and a completely flat object to one- surfaces of objects 1 and 2 measured others are arranged in such a way that one becomes one between them. They have mirror-like character, being a narrow air wedge is created. If the object is completely the object 2 through which the light passes, just like that, the interference fringes are linear and partially semipermeable. The opposite upper allele to each other. Curved interference fringe areas of 1 and 2 are at an angle ψ indicate surfaces that are not completely flat. If you incline, you close an air wedge between you the glass plate as a completely flat reference surface. The opposing surfaces can used, can also be curved from the interference image on the plane. unevenness or unevenness of the surface of the counter 60 The measuring device is similar to the Michelson inter- stand to be closed. ferometer. A group of point spreads 6 is shown in In the Michelson interference microscope or the focal plane 4 of an objective 3 as a result of an am Linnik will evaluate this phenomenon. Refe- air wedge between 1 and 2 occurring multiple The reference and test levels are spatially separated, but the reflection of the light beam 5 is shown. The however, show the same effect as two one 65 light beam 5 is that of a half-through Contacting surfaces that form air wedges, components let through if the mirror is allowed to pass through. the they are not exactly at right angles to each other. Distance between the point spread groups is It works similarly in "Optics for Constructors", 2 t / "/, where / is the focal length of the lens 3.