JPH0254921B2 - - Google Patents

Description

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

Conventionally, a so-called 45° mirror, which is tilted at 45° with respect to the incident optical path, is generally used to polarize the incident light beam in a direction 90° from the direction of incidence. 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. reflectance 100
% is desirable. However, the reflectance is 100%
It is extremely difficult to realize a mirror like this. A commonly used 45° mirror, as shown in FIG. When forming a film, a reflectance of 85% can be obtained with Al, which is typically used, and a reflectance of only about 95% with Ag. On the other hand, in the case of dielectric multilayer films, it is theoretically possible to increase the reflectance to over 99.9%, approaching 100%, by increasing the number of films, but as the number of film layers increases, manufacturing technology and manufacturing Cost problems arise.
Also known is a light deflecting prism 13 with a triangular cross section that utilizes total reflection of the prism as shown in Figure 2, but in this prism 13, 100% reflection is achieved at the reflecting surface Q that forms an angle of 45° with the optical path. Even if the rate is obtained,
Since it is impossible to completely reduce the reflection at the entrance plane P and the exit plane R that are perpendicular to the optical path, it is impossible to deflect 100% of the total incident energy I ₀ in the 90° direction.

The present invention was made for the purpose of a total reflection prism that can achieve a reflectance of 100%.Basically, an incident light beam that enters in a direction of 45 degrees with respect to an incident surface is reflected by the incident surface. The idea is to obtain a total reflection prism with substantially 100% reflectance by matching the direction of the light beam that enters from the incident surface, is totally reflected on the reflective surface, and then exits through the incident surface. This was done based on.

The total reflection prism of the present invention, which was completed based on this idea, basically consists of a bottom surface, a top surface parallel to the bottom surface, and a left-right symmetrical prism that makes an acute angle to the bottom surface and an obtuse angle to the top surface. It has an isosceles trapezoidal cross section with reflecting surfaces on both sides, and the bottom surface forms an entrance surface, and the other both side surfaces and the top surface form total reflection surfaces. Each of these surfaces is incident on the bottom surface at an angle of 45 degrees, and after being totally reflected on both reflective surfaces and the top surface, the direction of the light ray exiting from the same position as the above incident position on the bottom surface is the same as the direction of the light beam on the bottom surface. Its position and the angle between each surface are set so that it forms an angle of 90° with respect to the incident light, which is the same direction as the direction of the light ray directly reflected at the surface.

Furthermore, for such a total reflection prism, specifically, at least, where γ is the acute angle formed by the bottom surface and the reflecting surfaces on both sides, and n is the refractive index of the prism, γ=45°+sin ^-1 (√2/2n) It can be obtained by creating the ratio b/a of the length a of the bottom surface and the distance b from the bottom surface to the top surface to satisfy the relationship b/a=2sinγ/(sinγ+cosγ).

The invention will now be described with reference to illustrated embodiments. FIG. 3 shows a first embodiment of the present invention, and shows a specific example of the shape and an example of the optical path when the refractive index n of the prism is n=1.50. This total reflection prism consists of a bottom surface 20, a top surface 21 parallel to the bottom surface 20, and left-right symmetrical side surfaces 22, 22 connecting the bottom surface 20 and the top surface 21. Both side surfaces 22 make an acute angle γ with respect to the bottom surface 20. Therefore, it forms an obtuse angle with respect to the upper surface 21, and has an isosceles trapezoidal cross section as a whole.

The length of the bottom surface 20 is a, and the height of the trapezoid is
That is, if the distance between the bottom surface 20 and the top surface 21 is b, then a, b and the above γ satisfy each of the above conditions. That is, γ=73.13° and b=1.535a.

In the total reflection prism having the above configuration, the bottom surface 20
When a light beam is incident on point A at the center of the plane at an incident angle of 45 degrees, a portion of the light beam is reflected by the surface of the bottom surface 20 in a direction that is 90 degrees with respect to the incident direction, depending on the reflectance at the bottom surface 20. Assuming that the energy of the incident light is I ₀ and the reflectance at the bottom surface 20 is R, the energy of the light that is deflected by this surface reflection in a direction that is 90° with respect to the direction of incidence is I ₀ R. If the bottom surface 20 is not coated with any coating, the value of R is R=
Although the value of R is 0.04 (4%), even if an appropriate coating is applied so that the value of R takes on any value other than this, the present invention will still work as long as the coating does not absorb light.

On the other hand, the remainder of the optical energy reflected by the surface of the bottom surface 20, ie, I ₀ (IR), 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 point B on the top surface 21. The light is incident on the point at an incident angle β (in this example, β = 61.87°). The light incident on point C is reflected here and reflected again at point D on the next side 22.
It returns to point A after being reflected by a 90° deflection. Point B,
The reflectance at points C and D is 100% (total reflection) because the angle of incidence at each of these points is greater than the critical angle of the prism (41.81° in this example), and the light ultimately enters the prism. light energy I ₀
(IR) will return to point A as it is.
Here, the light energy is again divided into what passes through the bottom surface 20 and what is reflected by the bottom surface 20, but the energy of Io (1-R) (1-R) goes out of the prism and is first Like the light reflected from the bottom surface 20, it is emitted in a direction that is 90 degrees to the direction of incidence of Io.

On the other hand, the energy of Io(1-R)R is reflected back into the prism and returns to point B, the same as the first incident light.
It undergoes total reflection at points C and D and returns to point A, where the light Io(1-R) ² R is emitted in a direction that is 90° with respect to the direction of incidence of Io.

As a result of such repeated reflections occurring within this prism, the total energy I of the light that is deflected in the direction of 90 degrees with respect to the incident light is obtained by adding up the repeated reflections infinitely, and is calculated as I = IoR + Io (1 -R) ² +Io(1-R) ² R+ Io(1-R) ² R ² +Io(1-R) ² R ³ +... =Io(R+(1-R) ² (1+R+R ² +R ³ ...) ) becomes.

Since R<1, this infinite series ends up being I=Io(R+(1-R) ² /(1-R))=Io, and all the incident light energy is in the direction of incidence and 90
It will be deflected in the direction of the angle. In other words, the reflectance of this prism is 100%.

This infinite series is established in the range where the position of the light incident on the bottom surface 20 and the position of the light beam reflected within the present prism and emitted from the bottom surface 20 match. That is, in the above example, the size of the effective beam of light that can be incident on the bottom surface 20 is within the range shown by the broken line in FIG. 3, and using the length a of the bottom surface 20,
It can be expressed as a diameter of 0.202a.

FIG. 4 shows a second embodiment of the present invention,
An example is shown in which the refractive 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 γ=65.71° from the above equation, and the ratio of the length a of the bottom surface 20 to the height b of the trapezoid is b=1.387a.
In this embodiment, the incident light is incident on the bottom surface 20.
A ray that is incident at 45 degrees and enters the prism at a refraction angle α (α = 20.70 degrees) has an incident angle of 45 degrees at points B and D, and an incidence angle β at point C of β = 69.30. Since both of these prisms exceed the critical angle of 30°, 100% of the incident light energy can be deflected by 90°, just like the first embodiment.

Further, in this embodiment, the effective diameter of the incident light beam can be expressed as a diameter of 0.101a in the portion surrounded by the broken line in FIG. 4 using the length a of the bottom surface 20. As can be seen from the range of the beam of light 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, 22 through which the light rays do not pass are cut off, the function of the total reflection prism with 100% reflection is not lost at all. The same applies to the first embodiment.

As described above, the total reflection prism of the present invention can deflect a light beam by 90° with 100% reflectance, so it can be used as a reference reflective object when measuring the reflectance of a general reflective object. can.
That is, conventionally, in order to measure the reflectance of a 45° mirror, for example, as shown in FIG. The energy I of the light is measured and the reflectance R is measured as R=I/Io, but this measurement method requires the light receiving element 30 to be moved, making the apparatus complicated. 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 reflectance of the subject can be easily measured by determining the ratio between the light energy reflected by the subject and the energy of the light reflected by the total internal reflection prism.

Other effects of the total reflection prism of the present invention are listed below.

(1) Even if no reflection-enhancing film or anti-reflection film is applied to the polished surfaces of the bottom, top and both sides,
Since it is possible to deflect 100% of the energy of the incident light by 90 degrees, it becomes possible to manufacture inexpensive high-reflection prisms.

(2) Conversely, if there is a transparent film that does not absorb light on the bottom surface where light enters, no matter what kind of material is attached to it, it will be possible to deflect 100% of the light energy in the 90° direction. Therefore, if the total reflection surfaces on the top and both sides are sufficiently protected, you can obtain a highly reflective prism that is resistant to dirt on the bottom and can withstand long-term use and storage.

(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 or reflective prisms, and can be used to measure the reflectance (absolute reflectance) at an angle of incidence of 45°. It becomes easier.

[Brief explanation of the drawing]

Figure 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. FIG. 3 is a diagram of the principle when measuring the reflectance of 20...Bottom surface, 21...Top surface, 22...Side surface.

Claims (1)

[Scope of Claims] 1. A prism having a bottom surface, a top surface parallel to the bottom surface, and symmetrical reflecting surfaces on both sides making an acute angle with the bottom surface and an obtuse angle with the top surface, the prism having a diameter of 45 mm with respect to the bottom surface. The direction of the ray of light that enters at an angle of °, is totally reflected by the reflective surfaces on both sides and the top surface, and then exits from the same position as the above incident position of the bottom surface is the same as the direction of the ray of light that is directly reflected by the bottom surface. A total reflection prism characterized in that the positions of each of the surfaces and the angles between the surfaces are set so as to form an angle of 90° with respect to light.