JPS60242304A - Hologram interferometer for measuring surface shape of large-aperture plane mirror - Google Patents

Abstract

PURPOSE:To enable measurement of the surface shape of a large-aperture plane mirror by providing a hologram interference system having an optical system for reference light and an optical system for illuminating light and observing the interference fringe between the reconstructed object light reconstructed by a hologram and the illuminating light. CONSTITUTION:A hologram interferometer 1 is constituted of a laser light source 3, the optical system 4 for reference light provided with a reflection mirror M1, a microscopic objective lens MO1 and a pinhole P1 and a hologram HP and the optical system 6 for illuminating light provided with reflection mirror M3, a microscopic objective lens MO3 and a pinhole P3. The set position of the plane mirror MM to be inspected is set as specified. The parallel light from the laser light source 3 is split by a beam splitter BS1. One of the luminous fluxes is made incident on the hologram HP via the system 4 and the object light is reconstructed. The other luminous flux is passed through the system 6 to form the illuminating light which is reflected by the mirror surface MM and is then made incident on the hologram HP then the interference fringe is generated by the reconstructed object light and the reference light and therefore the measurement of the surface shape is made possible.

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 usually have a diameter of 20 cm or less and an accuracy of about 0.5 μm. However, with the recent development of diamond lathes, it has become relatively easy to manufacture metal mirrors with a diameter of about 1 meter, and the precision of these mirrors is approaching that of glass mirrors, although they are still far behind. However, no technology has been developed to easily measure these large-diameter mirror shapes with high precision.

By the way, the shape of a mirror with a diameter of about 10 cm has traditionally been determined using a Michelson interferometer, a Fizeau interferometer, etc.
It can be easily measured with an accuracy of about ,025μ.

[Problems to be solved by the invention] However, if this measurement principle is applied to the measurement of a plane mirror with an aperture of 1 m or more, then a lens with a diameter of 1 m or more and a
A semi-transparent mirror with a diameter of 1 m or more is required, and a standard mirror surface with a diameter of 1 m or more is required, and manufacturing these large measuring optical parts requires a lot of rotation technically and is extremely expensive. It is expensive and difficult to put into practical use. In addition, to measure such large-diameter mirror surfaces, we applied the previously established hacksaw measurement technique for small-diameter mirror surfaces, and measured the large-diameter plane mirror by dividing it into small-diameter interferometers. However, when measuring surface roughness, it is sufficient to sample only a portion of the mirror surface to be inspected. A relative error between a point at one end and a point at the opposite end is not detected, and therefore the method of measuring in this division 1) is likely to be accompanied by measurement errors.

This invention has been made in view of the above circumstances, and provides a measurement technique that can easily, reliably, and inexpensively measure the surface shape of a large-diameter plane mirror, and can also measure the surface shape at once 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 generates a laser light source and a reference light of a diverging spherical wave. a hologram in which a divergent spherical wave object light is recorded by the reference destination; 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. Preparation 2: The object light and the illumination light are arranged at a position where the object light and the illumination light are 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, there is a 11.1 hologram interference frame.

Hologram interference a) 1 comprises a hologram HP.

Therefore, regarding the production of 4゛ hologram 1-IP [Explanation J
Ru.

In Figure 2, 2 is 1 gura 1. , is an optical system for producing l-IP. The optical system 2 includes, for example, a sea 11 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 semitransparent mirrors) BS1 and BS2.

The reference light optical system 4 includes a reflecting mirror M1 and a microscope objective lens 40.
1. The object light optical system 5 is equipped with a pinhole P1. 9. The object light optical system 5 includes a reflecting mirror M2, a microscope objective lens MO2, and a pinhole P2.
It is equipped with

When producing a bologram I-IP, the laser beam from the laser light source 3 is split into two beams by the beam splitter BS1, one beam is input into the reference beam optical system 4, and the laser beam is split into two beams by the beam splitter BS1. l) 15 microscope with optical path changed by I mirror M1 = iJ object lens Mo1
, a reference beam of a diverging spherical wave is generated by the pinhole P1. The other beam is further split by a beam splitter BS2 and input into an 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. This object light is exposed and recorded on a photographic plate at the position of the bologram I-IP using the reference light, and is photographically processed to produce a hologram 1-I.
P is completed and soldered to the original position.

The interferometer 1 shown in FIG. 1 is shown in FIG. This is the setting.

Illumination light optical system 6, reflecting mirror M3, microscope objective lens N4o
3. It consists of a bottle ball P3, has the same structure as the object light optical system 5, and generates a diverging spherical wave illumination light. and,
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,
Therefore, the optical path of the object light reaching the hologram l\HP when it is assumed that the flat mirror surface MM to be tested does not exist matches the optical path of the illumination light reaching 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 object light optical system 5 and the illumination light optical system 6, so that the object light and the illumination light both enter the hologram 1-(P, and the object light and the illumination light enter the hologram HP). What is necessary is to search for a position where the object light and the illumination light coincide and no interference fringes occur.

[Operation] In order to measure the surface shape of the flat mirror surface MM to be measured in the hologram interferometer 1 as shown in FIG. 1, parallel light from the laser light source 3 is split by the beam splitter BS1, and one beam is guided to the reference beam optical system 4 to generate a reference beam in the form of a divergent spherical wave, which is incident on the hologram HP.
Record the object beam and reproduce it. Then, the other light beam is guided to the illumination light optical system 6 to generate a diverging spherical wave illumination light, and after being mixed with the flat mirror surface MM to be tested, a hologram HP is generated.
incident on .

Sai: Since the illumination light is influenced by the unevenness of the mirror surface of the flat mirror surface MM to be tested and deviates from the standard object light, interference fringes as shown in FIG. 3 are generated between the reproduced object light and the illumination light.

The interference fringe pitch D deviation (fld) in this interference fringe.

The shape error △h of the surface to be inspected is Δh−, where λ is the wavelength.
Since the relationship is (d/D)·(λ/2), the surface shape of the flat mirror surface MM to be tested can be measured by determining the shape error Δ1) from the interference fringe pitch D and the deviation ff1d.

(c) Effects of the invention As described above, according to the hologram interferometer of the present invention, it is necessary to prepare a hologram HP that is approximately the same size as the flat mirror surface to be tested. The conventional small 1] diameter lenses and semi-transparent mirrors can be used as they are, and there is no need for a standard mirror surface.
It is easy to manufacture and can be manufactured at low cost. Moreover,
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 interference training body.

In addition, without dividing and covering the entire mirror surface to be inspected, it is possible to 'M3B32 BSI

Claims (1)

[Claims] A laser light source, a reference beam optical system that generates a reference beam of a diverging spherical wave, a hologram in which an object beam of a diverging spherical wave is recorded by the reference destination, and a divergent spherical surface equivalent to the object beam optical system that generates the object beam. an illumination light optical system that avoids generating wave illumination light; a test plane mirror surface is arranged at a position where the object light and the illumination light are symmetrical; and the illumination light is reflected by the test plane mirror. After that, the hologram is illuminated, and the reference light is illuminated on the hologram to observe interference fringes between the reproduced object light and the illumination light illuminated on the hologram. Hologram interferometer for measuring the surface shape of large-diameter plane mirrors