JP2601278B2 - hologram - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a hologram (also referred to as a hologram screen) used in a grazing incidence interferometer using a holographic technique and recording and reproducing interference fringes.

(Prior Art) A hologram used in a conventional oblique incidence interferometer or the like is a fifth hologram.
As shown in the figure, a transparent glass substrate 50 is composed of a glass dry plate in which a photosensitive material 52 such as an emulsion is coated on one surface 50b, or as shown in FIG. A protective glass 56, which is a transparent protective member for protecting 52, is bonded and adhered with an adhesive 54.

When recording on this hologram, for example, as shown in FIG. 7, an opaque paint 54 is applied to the surface 50a of the glass substrate 50 opposite to the surface on which the photosensitive material is applied, or blackened. A so-called backing process is performed. This backing process is performed by the recording light R ₁ and R ₂ being incident on the photosensitive material 52 and then refracted and transmitted and reflected on the surface 50 a of the glass substrate 50, and on the boundary surface 50 a between the glass substrate 50 and the photosensitive material 52. This is to prevent the occurrence of interference fringes due to interference with the light reflected by the boundary surface 50b caused by the difference in the refractive index, thereby erasing coarse interference fringes that are visible to the naked eye and cause noise during hologram reproduction. It is possible to do.

Next, when reproducing the hologram, the backing-treated paint or the like is dropped, and the transparent substrate shown in FIG.
Return to 50. When reproduction light beams L ₁ and L ₂ conjugate to the parallel light beam at the time of recording enter the transparent glass substrate 50 of the hologram, the hologram converges this light beam to a point P on the optical axis. In the grazing incidence interferometer, the reproduction lights L ₁ and L ₂ carry interference fringes representing irregularities on the surface of the test object.
If a camera or the like is installed, the interference fringes can be observed.

(Problems to be solved by the invention) By the way, at the time of reproducing the hologram, FIG.
In the hologram shown in the figure, the surfaces 50a and 5
0b are formed in parallel with each other or the surfaces 56a and 56b of the protective glass 56 are formed in parallel, the hologram reproduction lights L ₁ and L ₂ incident on the glass substrate 50 50b and by reflecting at 50a, or a hologram reproducing light L _10, L ₁₁ is the surface 56a of the protective glass 56, 5
By reflecting at 6b, unnecessary and harmful interference fringes are generated between the internally reflected light and the normally refracted transmitted light. The interference fringe based on the internal reflection is difficult to distinguish from the normal interference fringe based on the test surface of the subject, and there has been a problem that the test surface cannot be inspected correctly.

The present invention is to provide a hologram that can solve such a problem.

(Means for Solving the Problems) In view of the above, the present invention provides
In a hologram recorded on a photosensitive material applied to one surface of a transparent substrate, internally reflected refracted transmitted light that is refracted and transmitted after being internally reflected between the incident surface side of the transparent substrate and the photosensitive material coated surface side The incident surface of the substrate is made non-parallel with a wedge-shaped cross section with respect to the photosensitive material application surface so that the interference fringe noise generated by the light and the normal refracted transmitted light is higher than the spatial frequency at which the visible light cannot be visually recognized.

(Operation) According to the hologram, when a transparent substrate and a photosensitive material, for example, glass are used as the transparent substrate, the presence of an interface caused by a difference in refractive index between the photosensitive material and the refractive index of glass is 1.54 to 1.54. It is possible to make harmful interference fringes generated by the internally reflected light of the substrate and the normally refracted transmitted light generated less noticeable.

Therefore, when used in an interferometer, it is possible to differentiate interference fringes based on the test surface of the test object from harmful interference fringes generated by internal reflection in the transparent substrate, and accurately measure the surface accuracy of the test surface. It can be inspected.

(Example) Hereinafter, the hologram of the present invention will be described in detail based on an example shown in the accompanying drawings.

Figure 1 shows a first embodiment of a hologram according to the present invention, structure and hologram reproducing light A of the hologram H ₁ according to the invention. FIG Ru explaining interferences caused by B. In FIG. 1, and a hologram H ₁ Emulsion 20. is a photosensitive material mainly composed of transparent glass substrate 10 and the transparent gelatin applied to a surface of the one. The surface 10b on the emulsion side of the glass substrate 10 is a flat surface, and the surface 10a on the opposite side is inclined at an angle θ with respect to the surface 10b.
Is formed in a wedge-shaped cross section having a wedge angle θ, and the emulsion 20 is applied to the flat surface 10b of the glass substrate.

The laser beam A coherent to the hologram H _1, when the incident as a hologram reproducing light B, light rays A glass substrate
After being internally reflected on the surfaces 10b and 10a of FIG. 10, the light is refracted and transmitted to become a light beam A ', and the light beam B is refracted and transmitted without being internally reflected in the hologram to become a light beam B'. Will do.

This interference effect will be described in more detail with reference to FIG. 4 which is an enlargement of FIG. 1. In FIG.
The light beam A incident on the surface 10a of FIG. 10 at an incident angle i becomes a light beam A 'refracted at a refraction angle i' at 10a, and the angle (i'-
θ), the ray A ″ is reflected at the surface 10a at an angle (i′−2θ), and the ray A is reflected.
Ray B incident on the intersection C between the surface 10a and the ray A "at an incident angle i
Becomes a light beam B 'refracted at the refraction angle i'.

The light ray A and the light ray B 'interfere with each other to generate an interference fringe. The spatial frequency d of the interference fringe on the surface 10b is d = {sin (i'-. Theta.)-Sin (i'-3.theta.)} /. Lamda. ... (1)

For example, the refractive index n = 1.5 and the incident angle i = 80 of the glass substrate 10
Assuming that ゜, i ′ = 41.04 °, and if the wavelength λ = 632.28 nm, the relationship between the wedge angle θ and the spatial frequency d is as follows.

Therefore, for example, when the wedge angle θ is 0.3 °, assuming that the surfaces 10a and 10b are good planes, 1
2.6 interference fringes / mm are generated. When a hologram formed on the photosensitive material coated on the surface 10b is illuminated by such a plane wave on which the interference fringes are superimposed, 12.6 lines / mm of interference fringes appear to be superimposed on the hologram surface. So that it is virtually invisible to the naked eye.

FIG. 2 is a diagram showing a second embodiment of the hologram according to the present invention. In the figure, the hologram H ₂ is obtained by adding a protective glass 30 is further transparent protective member on the hologram H ₁ shown in Figure 1. The protective glass 30 has a plane 30a on the emulsion 20 side and a plane 30b on the opposite side.
It is formed in the same manner sectional wedge shape and the glass substrate 10 an angle theta ₂ inclined with respect to a. The flat surface 30a is bonded to the emulsion 20 with an adhesive 22. As the refractive index of the adhesive 22, one having a value close to the refractive index of each of the glass substrate 10 and the protective glass 30 is selected and used. By thus configuring the hologram H _2, is prevented from dust or scratches on the emulsion 20 is attached. Even further bonding the protective glass 30 to the emulsion 20, harmful interference fringes well as occurs in the substrate glass 10, for example by a wedge angle theta ₂ of the protective glass 30 to 0.3 °, the protective glass 30 An internal reflection transmitted light (not shown) based on internal reflection by reflection at an interface with the emulsion 20 (formed by a refractive index difference between the refractive index of glass: 1.5 and the refractive index of emulsion: 1.54); The interference fringes between the transmitted light C 'internally reflected in the substrate 10 and the interference fringes are 25.2 times, twice as large as 12.6 lines / mm.
12.6 lines / mm interference fringes with normal transmitted light D '
And cannot be seen with the naked eye, and can be differentiated from regular interference fringes.

Figure 3 is shows a third embodiment of a hologram of the present invention, the hologram H ₃ is the conventional hologram structure comprising a transparent glass substrate 14 and the emulsion 20 of the substantially parallel planes, further wedge angle is constructed by laminating the adhesive, respectively a transparent protective glass 30 having a transparent glass substrate 12 and the wedge angle theta ₄ with theta ₃ adhesives 24 and 22. Transparent glass substrate 12, a glass substrate 14-side surface 12b is a surface 12a on the opposite side in plan has an angle theta ₃ inclined with respect to surface 12b.
Protective glass 30, the surface 30a of the emulsion 20 side in the plane, the plane 30b of the opposite side is the angle theta ₄ inclined with respect to the surface 30a. adhesive
The refractive indices of 24 and 22 are based on the glass substrates 12, 14 and the protective glass 3.
Those having refractive indexes substantially close to 0 are selected and used.

By configuring the hologram H ₃ as described above,
The hologram H ₃ laser beam incident refracted and transmitted to the hologram reproducing light E ', F' harmful interference fringes due to not be macroscopic, for the reason similar to the above embodiment. In addition, an antireflection film cannot be directly provided on the surface 14a of the glass substrate 14 from the viewpoint of the heat resistance of the hologram.
It is possible to form an anti-reflection film on the surface 12a of the glass substrate 12 by bonding the anti-reflection film to the emulsion surface, as in the previous embodiment. And light loss due to reflection can be reduced as much as possible.

(Effect of the Invention) As described above, according to the hologram according to the present invention, when a transparent substrate and a photosensitive material, for example, glass is used as the transparent substrate, the photosensitive material has a refractive index of 1.5 and a refractive index of 1.54. Harmful interference fringes generated by the internally reflected light of the substrate and the normally refracted transmitted light caused by the presence of the interface caused by the difference in the refractive index can be made inconspicuous. Also,
When glass is used similarly as the transparent protective member by configuring as in the second and third embodiments, harmful interference fringes generated by the internally reflected light and the normally refracted transmitted light in the transparent protective member are not noticeable. Is what you can do.

Therefore, when used in an interferometer, it is possible to differentiate interference fringes based on the surface to be inspected of a subject from harmful interference fringes caused by internal reflection of the transparent substrate and the transparent protective member, and to improve the surface accuracy of the surface to be inspected. Can be measured and inspected correctly.

[Brief description of the drawings]

FIG. 1 is an explanatory view of one embodiment of a hologram according to the present invention, FIG. 2 is a plan view showing a second embodiment of the hologram of the present invention, and FIG. FIG. 4 is an enlarged view of FIG. 1, FIGS. 5 and 6 are explanatory diagrams showing a conventional hologram, and FIG. 7 is an explanatory diagram showing a conventional hologram formation. It is. H1, H2, H3 hologram, 10, 12, 14 transparent glass substrate 20 emulsion (photosensitive material), 30 protective glass (transparent protective member) θ, θ1, θ2, θ3, θ4 wedge Corner

Claims (1)

(57) [Claims] In a hologram recorded on a photosensitive material applied to one surface of a transparent substrate, the hologram is refracted and transmitted after being internally reflected between the incident surface side and the photosensitive material applied surface side of the transparent substrate. The incident surface of the substrate was made non-parallel to have a wedge-shaped cross section with respect to the photosensitive material application surface so that interference fringe noise generated by the internal reflection / refraction / transmission light and the normal refraction / transmission light becomes invisible spatial frequency or higher. A hologram, characterized in that: