JPS6091301A - Total reflection prism - Google Patents

Abstract

PURPOSE:To obtain a total reflection prism with a 100% reflection factor by making the reflection direction of 45 deg. incident light on an incidence surface coincident with the light beam direction in which the incident light is reflected totally by reflection surface and then projected through the incidence surface. CONSTITUTION:The total reflection prism is sectioned in an isosceles trapezoid shape, and has the base as the incidence surface and other flanks and the top as total reflection surfaces. The respective surfaces are so formed that when the incident light is at 45 deg. to the base, the light beam projected from the base after total reflection on both sides and the base is at 90 deg. to the incident light as well as the light beam reflected directly by the base. Then, gamma=45 deg.+sin<-1>(2<1/2>/2n) where gamma is the angle of the base to both side reflecting surfaces and (n) is the refractive index of the prism, and the ratio b/a of the length (a) of the base and the distance (b) to the height of the trapezoid is b/a=2singamma/(singamma+cosgamma).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a total reflection prism that reflectively bends an incident light beam by 90 degrees.

Conventionally, in order to deflect the incident light beam in the direction of 80° from the incident direction, it is conventionally necessary to deflect the incident light beam at 45° with respect to the incident optical path, so-called 45°.
Mirrors are commonly used. This 45° mirror is often used in optical devices that use single-wavelength light sources such as lasers, but in many cases, these optical devices are used to eliminate energy loss during reflection, that is, to eliminate energy loss during reflection. It is desired that the reflectance be 100%. However, it is extremely difficult to realize a mirror with a reflectance of 10 oz. A commonly used 456 mirror consists of a surface mirror in which a metal or dielectric multilayer mirror film 12 is formed on the surface of a substrate 11, as shown in FIG. In the case of typically used AI, the reflectance is 85z, and in the case of Ag, the reflectance is 95z.
% reflectance can only be obtained. On the other hand, in the case of dielectric multilayer films, theoretically, if the number of films is increased, the reflectance can be increased to 119
．． Although it is possible to get close to 100% at 9% or more,
As the number of membranes increases, problems arise in terms of manufacturing technology or manufacturing costs. In addition, a light deflecting prism 13 with a triangular cross section that utilizes total reflection of the prism as shown in Fig. Even if a reflectance of % is obtained, it is not possible to completely reduce the reflection at the entrance plane P and exit plane R, which are perpendicular to the optical path, so the total incident energy IO is deflected in the 100X, 906 direction. It is not possible.

The present invention was made for the purpose of a total reflection prism that can achieve a reflectance of 100%, and basically has a reflectance of 45
The direction of the incident light ray that enters in the direction of ° is reflected by the incident surface, and the direction of the light ray that enters from the incident surface, is totally reflected by the reflective surface, and then exits through the incident surface. This was done based on the idea of obtaining a total reflection prism with a reflectance of substantially 1001.

The total reflection prism of the present invention, which was completed based on the idea mentioned above, basically has a bottom surface, a top surface parallel to this bottom surface, and an acute angle to the bottom surface [an obtuse angle to the two surfaces]. It has an isosceles trapezoid cross section with symmetrical reflecting surfaces on both sides, with the bottom surface forming an incident surface and the other both side surfaces and the top surface forming total reflection surfaces. and each of these faces is 45
The direction of the ray of light that enters at an angle of 90 degrees and exits from the bottom surface after being totally reflected on both reflective surfaces and the top surface is 90 degrees to the incident light, which is the same as the direction of the ray that is directly reflected on the bottom surface.
The position and the angle between each surface are set so as to form an angle of .

Furthermore, such a total reflection prism has at least the following equation: 7 = 45" + sin→
(# / 21+), and the ratio b/a of the length a of the bottom surface to the distance #b from the bottom surface to the top surface is b/a=2s in y / (s in y +co
It can be obtained by creating it so as to satisfy the relationship s y ).

The invention will now be described with reference to the illustrated embodiments. FIG. 3 shows the first embodiment of the present invention, in which the refractive index n of the prism is
shows a specific example of the shape when n=1.50 and an example of the optical path at that time. This total reflection prism has a bottom surface 2
0, a surface 21 parallel to this bottom surface 20, and the bottom surface 20
It consists of both symmetrical side surfaces 22 and 22 connecting the upper surface 21 and the upper surface 21, and the both side surfaces 22 form an acute angle γ with the bottom surface 20, and extend beyond the surface and form an obtuse angle with the 1-surface 21. The cross section as a whole is trapezoidal with each leg.

If the length of the bottom surface 20 is a, and the height of the trapezoid, that is, the distance between the bottom surface 20 and the top surface 21 is b, then a, b, and the above-mentioned γ satisfy each of the above conditions. That is, y
=73.13', b=1.535a.

In the total reflection prism with the above configuration, when a light beam is incident on point A at the center of the bottom surface 20 at an incident angle of 45°, the bottom surface 20
Depending on the reflectance at , a part of the light is reflected by the surface of the bottom surface 20 in a direction 90@ with respect to the incident direction. If the energy of the incident light is IQ, and the reflectance at the bottom surface 20 is R, then the energy of the light deflected by this surface reflection in a direction 80" from the incident direction is IOR. The value of H is, if this bottom surface 20 If there is no coating applied to the The present invention can be applied as long as it is a coating.

The remainder of the light energy reflected by the other surface of the bottom surface 20;
That is, I o (1-R) enters the present prism. This light travels through the prism at the bottom surface 20 at an angle α (α-28,13' in this example) according to the law of refraction, is reflected at point B on the side surface 22 with a 90° deflection, and then is reflected at the top surface 21. The angle of incidence β (in this example, n = 81.8°
) is incident. The light incident on the 0 point is reflected here, and is reflected again at the 0 point on the next side surface 22 with a deflection of 90'' and returns to the A point.B.

The reflectance at point, 0 point, and 0 point is determined by the fact that the angle of incidence at each point is the critical angle of the prism (in this example, 41
．． 81°), so it becomes 100% (total reflection), and the energy of the light incident on the prism ends up being I o (1
-R) will return to point A as it is. Here, the energy of the light is again divided into what passes through the bottom surface 2o and what is reflected by the bottom surface 20, but I o (1-R) (
1-R) exits the prism and is emitted in a direction 90' to the direction of use of the IO, similar to the light initially reflected at the bottom surface 20.

On the other hand, the energy I (1
-R) 2 R light is emitted in a direction that is 80" from the incident direction of beam 0.

As a result of such repeated reflections occurring within this prism, the total energy of the light that is deflected in the 90' direction relative to the incident light is obtained by adding up the repeated reflections infinitely, and is given by: I=IoR+Io(1- R)2+ Io(1-R)2
R+l0(1-R)zR2+l0(1-R)2R'+
-i = I O(R÷(1-R)2(++R+R2+
R3##e)).

Since R<1, this infinite series ends up being I = I o
(R+(1-R)2/(1-R)) = I.

Therefore, all of the incident light energy is deflected in a direction that is 90 degrees to the incident direction. In other words, the reflectance of this prism is 100%.

In this example, the size of the effective beam of light that can be incident on the bottom surface 2o is within the range shown by the broken line in FIG. .

FIG. 4 shows a second embodiment of the present invention, in which the monthly refraction index n of the prism is n=2.0. At this time, the acute angle γ between the bottom surface 20 and the side surface 22 is calculated from the above equation as γ-85.71°, and the ratio of the length a of the bottom surface 2o to the height b of the trapezoid is b=1.38? It becomes a. In this embodiment, the incident angle is 45° to the bottom surface 2o, and the refraction angle α
(α-20,70”), the incident angles at points B and D are both 45°, and the angle of incidence β at point C is β=f19.30°. Since the critical angle 30' of this prism is exceeded, 100% of the incident light energy can be deflected by 90'', just like in the first embodiment.

Furthermore, in this example, the effective diameter of the incident light beam is the fifth
In the part surrounded by the broken line IN, the length a of the bottom surface 20 can be used to manipulate the diameter as 0.101a. As can be seen from the range of the light beam indicated by this broken line, only this range of the prism is used, and the other parts are not used. Therefore, as shown in FIG. 4, even if the portions of the side surfaces 22 and 22 through which the light rays do not pass are cut, the function of the 100% total reflection prism is not lost at all. The same applies to the first embodiment.

As described above, the total reflection prism of the present invention has a total reflection rate of 100
Since it is possible to deflect a light beam by 90 degrees with a 04% ratio, it can be used as a reference reflective object when measuring the reflectance of a general reflective object.

That is, conventionally, in order to measure the reflectance of a 45° mirror, for example, as shown in FIG.
and the energy I of the light after reflection is measured, and the reflectance R is determined by R
= I/Io, but this measurement method requires the light receiving element 30 to be moved, which complicates the apparatus. However, according to the total reflection prism of the present invention, using this as a reference object and using a commercially available double beam spectrometer, the light energy after being reflected on the subject and the energy of the light reflected by the water-metal reflecting prism can be determined. By calculating the ratio, the reflectance of the subject can be easily measured.

The effects of the total reflection prism of this thin ice invention are listed below.

(1) The energy of the incident light can be deflected by 100 degrees and 90 inches without applying any reflection-enhancing film or anti-reflection film to the polished surfaces of the bottom, top, and both side surfaces.
It is possible to manufacture inexpensive high-reflection prisms.

(2) Conversely, as long as there is a transparent film that does not absorb light on the bottom surface where light enters, it is possible to deflect the light energy in the 90° direction no matter what kind of material is attached to it. This effect is not lost, so if the total reflection surfaces on the top and both sides are sufficiently protected, a highly reflective prism that is resistant to dirt on the bottom and can be used and stored for a long time can be obtained.

(3) Since the effects of 100% reflection and 90° deflection do not change regardless of the polarization state of the incident light, a stable high-reflection prism that is not affected by changes in the polarization state caused by the optical system can be obtained.

(4) As mentioned above, it can be used as a reference mirror when measuring the reflectance of objects such as other reflective mirrors and reflective prisms, and the reflectance at an incident angle of 45° (absolute reflectance)
Measurement becomes easier.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an example of a conventional 45° mirror. Fig. 2 is a conceptual diagram of a conventional light deflection prism using a total reflection surface, Figs. 3 and 4 are cross-sectional views showing examples of the total reflection prism of the present invention, and Fig. 5 is a conventional reflection object. The principle diagram when measuring the reflectance of 20... bottom surface, 21...
・Top surface, 221. ,side. Same agent 3 Ml) Kuni Otsutsu Hat Figure 2 Figure 5” = 30 Figure 3 Figure 4 ■

Claims (1)

[Claims] (1) A prism having a bottom surface, a top surface parallel to the bottom surface, and symmetrical reflecting surfaces on both sides forming an acute angle with the bottom surface and an obtuse angle with the top surface, the prism having a 45° angle with respect to the bottom surface.
The direction of the ray of light that enters at an angle of A total reflection prism characterized in that the positions of the above-mentioned surfaces and the angles between the respective surfaces are set. (2. In claim 1, the acute angle γ between the bottom surface and the reflective surfaces on both sides is γ=45° + sin-' (J/2n), where n is the refractive index of the prism, and Ratio of length a to distance from bottom to top surface b/a
is a total reflection prism that satisfies the relationship b/a=2siny/(siny+cosγ).