JPH0223802B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Purpose of the Invention [Field of Industrial Application] This invention relates to a hologram interferometer for measuring the surface shape of a large-diameter plane mirror.

[Prior Art] Conventionally, plane mirrors have been made by polishing glass and depositing metal such as aluminum on its surface, and their size is usually within 20 cm in diameter.
The accuracy is about 0.5μ. However, with the recent development of diamond lathes, the diameter of the diamond lathe has increased to 1 m.
It has become relatively easy to manufacture metal mirrors of about 100 degrees, and although their precision is not as high as that of glass mirrors, it is approaching that level. Not developed.

By the way, the shape of a mirror with a diameter of about 10 cm can be easily measured with an accuracy of about 0.025 μ using a Michelson interferometer, Fizeau interferometer, etc.

[Problems to be Solved by the Invention] However, if this measurement principle is applied to the measurement of a plane mirror with a diameter of 1 m or more, it will be necessary to use a lens with a diameter of 1 m or more, a semi-transparent mirror with a diameter of 1 m or more, and a mirror with a diameter of 1 m or more. Standard mirror surfaces are required, and manufacturing such large measurement optical components is technically difficult and extremely expensive, making it difficult to put them into practical use. It is also conceivable to apply the established measurement technique for small-diameter mirror surfaces mentioned above to the measurement of such large-diameter mirror surfaces, and to measure the large-diameter plane mirror by dividing it with a small-diameter interferometer. However, when measuring surface roughness, it is sufficient to sample a portion of the mirror surface to be inspected, whereas in the case of the surface shape of a mirror surface, it is necessary to measure the entire surface at once. A relative error between it and the point at the other end is not detected, and therefore, this method of dividing and measuring tends to be accompanied by measurement errors.

The present invention was made in view of the above circumstances, and provides a measurement technique that allows the surface shape of a large-diameter plane mirror to be easily, reliably, and inexpensively measured at one time without dividing the mirror surface. is intended to provide.

(B) Structure of the invention [Means for solving the problem] In response to this purpose, the hologram interferometer for measuring the surface shape of a large-diameter plane mirror of the present invention includes a laser light source and a reference light of a diverging spherical wave. a hologram in which a diverging spherical wave object light is recorded using the reference light; and an illumination light optical system that is equivalent to the object light optical system that generates the object light and generates a divergent spherical wave illumination light. the object light and the illumination light are arranged in a position where the object light and the illumination light are line-symmetrical, and the hologram is illuminated after the illumination light is reflected by the test plane mirror; The hologram is illuminated with the reference light to observe interference fringes between the reproduced object light and the illumination light that illuminates the hologram.

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

In FIG. 1, 1 is a hologram interferometer. The hologram interferometer 1 is equipped with a hologram HP. First, we will explain the production of the hologram HP.

In FIG. 2, 2 is an optical system for producing the hologram HP. The optical system 2 includes, for example, a laser light source 3 that generates an argon ion laser, a reference light optical system 4, an object light optical system 5, and beam splitters (or semi-transparent mirrors) BS1 and BS2.

The reference light optical system 4 includes a reflecting mirror M1, a microscope objective lens Mo1, and a pinhole P1. The object light optical system 5 includes a reflecting mirror M2 and a microscope objective lens M0.
2. Equipped with pinhole P2.

When creating a hologram HP, the laser light from laser light source 3 is split into 2 parts by beam splitter BS1.
The light beam is divided into light beams, one of the light beams is input into the reference light optical system 4, and after the optical path is changed by the reflecting mirror M1, a reference light of a diverging spherical wave is generated by the microscope objective lens Mo1 and the pinhole P1. The other beam is further divided by a beam splitter BS2 and input into the object beam optical system 5, and after changing the optical path by a reflecting mirror M2, a diverging spherical wave object beam is generated by a microscope objective lens Mo2 and a pinhole P2. let This object light is exposed and recorded on a photographic plate at the position of the hologram HP using the reference light mentioned above, and is photographically processed to form a hologram.
The HP is completed and set in its original position.

The interferometer 1 shown in FIG. 1 is connected to the optical system 2 shown in FIG.
The beam splitter BS2 is removed from the previous model, an illumination light optical system 6 is added, and the set position of the flat mirror surface MM to be tested is set.

The illumination light optical system 6 includes a reflecting mirror M3, a microscope objective lens Mo3, and a pinhole P3, and has the same structure as the object light optical system 5, and generates a diverging spherical wave of illumination light. In addition, the illumination light optical system 6 is arranged so that the illumination light generated therefrom has line symmetry with respect to the object light with respect to the plane mirror surface MM to be inspected, and therefore the object light when it is assumed that the plane mirror surface MM to be inspected does not exist. The optical path in which the illumination light reaches the hologram HP coincides with the optical path in which the illumination light reaches the hologram HP after being reflected by the flat mirror surface MM to be tested. In order to determine the set position of the flat mirror surface MM to be tested, as shown in FIG.
A beam splitter BS3 is inserted between the hologram HP and the object light and the illumination light are configured so that they both enter the hologram HP. All you have to do is find a position where no stripes occur.

[Function] In the hologram interferometer 1 as shown in FIG. 1, in order to measure the surface shape of the plane mirror surface MM to be tested, parallel light from the laser light source 3 is split by the beam splitter BS1, and one beam is split into two parts. Reference light optical system 4
A diverging spherical wave reference beam is generated, which enters the hologram HP, and reproduces the object beam recorded in the hologram HP. The other light beam is guided to the illumination light optical system 6 to generate a diverging spherical wave illumination light, which is reflected by the flat mirror surface MM to be tested and then incident on the hologram HP.

The illumination light deviates from the standard object light due to the influence of the unevenness of the mirror surface of the flat mirror surface MM to be tested.
Interference fringes as shown in FIG. 3 are generated between the reproduced object light and the illumination light.

The relationship between the interference fringe pitch D in this interference fringe, the amount of deviation d, and the shape error △h of the surface to be measured is △h=(d/D)・(λ/2), where λ is the wavelength. The shape error Δh is obtained from the interference fringe pitch D and the amount of deviation d, and the surface shape of the flat mirror surface MM to be tested can be measured.

(C) Effects of the Invention As described above, according to the hologram interferometer of the present invention, only the hologram HP needs to be prepared with approximately the same size as the flat mirror surface to be tested, but other lenses and half-sized holograms need to be prepared. The conventional small-diameter transparent mirror can be used as is, and
It does not require a standard mirror surface, making it easy to manufacture and inexpensive. Furthermore, since a hologram that is approximately the same size as the plane mirror surface to be tested is not very expensive, its use will not significantly increase the price of the entire interferometer.

Furthermore, since the entire mirror surface to be inspected can be measured at once without dividing it, there is no room for measurement errors, and highly accurate surface shape measurement is possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a hologram interferometer for measuring the surface shape of a large-diameter plane mirror according to the present invention, FIG. 2 is a block diagram showing an optical system for producing a hologram, and FIG.
The figure is a diagram showing an example of interference fringes. 1...Hologram interferometer, 2...Optical system, 3...
...Laser light source, 4...Reference light optical system, 5...Object light optical system, 6...Illumination light optical system, HP...Hologram, M1...Reflector, Mo1...Microscope objective lens, P1...Pin Hall, BS1...beam splitter (or semi-transparent mirror), MM...plane mirror surface to be tested.

Claims (1)

[Claims] 1 A laser light source, a reference light optical system that generates a divergent spherical wave reference beam, a hologram that records a divergent spherical wave object beam using the reference beam, and a divergent object beam that is equivalent to the object beam optical system that generates the object beam. An illumination light optical system that generates spherical wave illumination light is provided, and a test plane mirror surface is arranged at a position where the object light and the illumination light are line-symmetrical, and the illumination light is transmitted to the test plane mirror. The hologram is configured to be illuminated after being reflected, and interference fringes between the reproduced object light reproduced by illuminating the hologram with the reference light and the illumination light illuminating the hologram are observed. A hologram interferometer for measuring the surface shape of large-diameter plane mirrors.