JPH03186805A - Polarizing prism - Google Patents

Abstract

PURPOSE:To obtain a polarizing prism having a wide visual field angle from an ultraviolet range up to an infrared range by constituting the polarizing prism of one scalene triangle prism and two right-angled triangle prisms, and forming respective joint parts by air layers. CONSTITUTION:The polarizing prism is constituted of two right-angled triangle prisms 1, 2 having respectively different apex angles S1, S2 and one scalene triangle prism 3 and respective joint parts 4 are formed by air layers. Since the ultraviolet range is covered with the prism 2 and a long wavelength range is covered with the prism 1, the polarizing prism can secure a wide visual field angle over a wide wavelength range wider than the case of S1 = S2. Thus, the polarizing prism capable of simultaneously satisfying both the wide transmitting wavelength range and wide visual field angle can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polarizing prism for a wide wavelength range used in spectrophotometers and the like.

[Prior art]

In spectrophotometers that measure transmittance and reflectance by irradiating a monochromatic sample with a diffraction grating, the polarization state of the incident light becomes a problem, especially when measuring at oblique incidence. The light separated by the diffraction grating becomes elliptically polarized light, which varies depending on the wavelength. However, what is important as a measured quantity is often the transmittance 1 reflectance for S waves and P waves. Therefore, in order to keep the power constant, a polarizing prism is inserted after the diffraction grating, and the prism is rotated to generate S-wave incident light and P-wave incident light. On the other hand, since a spectrophotometer is used for pre-metal measurement in a wide wavelength range from ultraviolet to infrared, such a polarizing prism has a wide transmission wavelength V.
' and must also function as a polarizer. Furthermore, in order to efficiently use the light that has been weakened by being separated by a single diffraction grating without reducing its intensity, it is preferable to have a wide viewing angle.

The viewing angle of a polarizing prism whose optical axis is in a plane perpendicular to the cross section of the prism will be explained with reference to FIG. Create three-dimensional orthogonal coordinate axes as shown in the drawing.

Let β be the angle between the X axis and the optical axis. Prism gold structure The principal refractive index of the uniaxial crystal for ordinary and extraordinary rays is 19nε, respectively, and the apex angle of the prism is S.

Assuming that the refractive index of the adhesive is in, the critical incident angles 1° and 2, at which the ordinary ray and the extraordinary ray are totally reflected at the joint, are given by the following equations, respectively.

5inI. = cossi-n5in8 In the Glan-Thompson prism, which is a typical polarizing prism, β = 90,
In a Franck Ritter prism, β = 45°. When the refractive index n of the adhesive is 1.43 in a calcite Glanmmun prism, 10 at a wavelength of 589.23 nm.
=I. If we find the apex angle s+2 of the prism so that

5 = 23.53° 0 The viewing angle of this prism 1.
Figure 5 shows the +1° wavelength dependence. As is clear from this graph, the Glan-Thompson prism has a wavelength of 300 nm.
From 1,400 nm to 1,400 nm, a wide viewing angle of 20' or more can be ensured at all times. However, the adhesive commonly used has the disadvantage that it does not transmit light at wavelengths below 300 NFFL due to absorption by the adhesive.

Examples of prisms that allow wavelengths of aeonm or less to pass through the tip include a Grand-Foucault prism with an air layer at the junction. In Grand-Foucault prism, n = 3 is sufficient. Wavelength: 589.231mK If we find the apex angle of the prism so that = 1°, then 5 = 50.46°. FIG. 4 shows the wavelength dependence of the viewing angle of this prism. Since Glan-Foucault prisms do not absorb light through adhesive layers, they can be used at wavelengths of 30 Qnm or less, but on the other hand, the viewing angle is around 8°, which is narrower than that of Glan-Thompson prisms.

[Problem to be solved by the invention]

Polarizing prisms used in spectrophotometers etc. require two performances: a wide transmission wavelength range and a wide viewing angle.
No conventional polarizing prism satisfies these two requirements at the same time. The Glan-Thompson prism, which has the widest viewing angle, cannot be used in a wavelength range of 300 nm or less, and the Glan-Foucault prism, which has a wide transmission wavelength range, cannot have a wide viewing angle.

An object of the present invention is to provide a polarizing prism that satisfies both a wide M wavelength range and a wide viewing angle.

[Means to solve the problem]

A polarizing prism of the present invention is shown in FIG. This prism consists of two right triangular prisms with different apex angles 81, 82, 2 and 3. Each joint 4 is formed of an air layer.

In addition, ψ. ,ψ. are the critical angles of the ordinary and extraordinary rays of the prism], ψ0. Da@ represents the critical angle of the ordinary and extraordinary rays of the prism 2.

[Effect]

The Ahrens prism is well known as a prism with a wide viewing angle. This is a right triangular prism glued to the two hypotenuses of an isosceles triangular prism.
As shown in Figure 3, it looks like two Glan-Thompson prisms lined up.

The critical angle between the ordinary and extraordinary rays of the prism on one side is 10 and 1.
．． Then, the viewing angle of the entire Ahrens prism is 2I0
When the apex angle sl of one rhythm is set so that X,=O, the viewing angle of the Ahrens prism becomes maximum.

However, as long as the joints of each prism are made of adhesive, it is difficult for ultraviolet light to pass through.
The joint is made into an air layer by using a foam. but.

As is clear from FIG. 5, as the wavelength becomes longer, 1.
becomes larger, but conversely, 1° becomes smaller, so the viewing angle of the prism becomes smaller. Therefore, in the present invention, the two prisms have different apex angles to obtain a wide viewing angle over a wide wavelength range. That is, in the figure, 81 is set so that φ6 is a negative value in the ultraviolet bait region, and 82 is ψ. Set it so that = 0. ψ as the wavelength becomes longer. , ψ6 increases, ψ. ,ψ. decreases, but always ψ. 〈ψ. and 51=S2 and ψ.

=φ. When the apex angle of the prism is set as = 0, the viewing angle ψ. Ten ψ. becomes larger. Tsumashi, prism 2
By covering the prism 1 with an ultraviolet suppressing gold layer and making the prism 1 cover a longer wavelength region, it is possible to secure a wide viewing angle over a wider wavelength region than when 5l=82.

〔Example〕

Viewing angle ψ when the apex angle of prism 1 is S+=49° and the apex angle of prism 2 is Sz=49.7°.

The wavelength dependence of +to is shown in FIG. However, in the ultraviolet region, φ. Since there is a wavelength range where <0, the viewing angle of this part is conveniently f6+ψ. And so. In this example, β-9
Although the direction of the optical axis is 0°, the direction of the optical axis is not limited to this.

〔Effect of the invention〕

The Glan-Thompson prism has a large viewing angle but does not allow ultraviolet light to pass through, while the Grand-Foucault prism allows ultraviolet light to pass through but has a small viewing angle. In other words, conventional polarizing prisms can be used in a wide wavelength range from ultraviolet light to infrared light1, and can always be used with
．． There was no such thing as having a field of view wider than 5 degrees.

Therefore.

When using polarizing prism gold over a wide wavelength range in a spectrophotometer, etc., a Grand-Foucault prism is used in the ultraviolet region, and a Glan-Thompson prism is used in the visible to infrared region (7). It was absolutely inevitable. However, the polarizing prism of the present invention can be used from the ultraviolet region to the infrared region and always has a viewing angle of 9.5° or more, so it is more versatile than conventional polarizing prisms and can be used in spectrophotometers, etc. Even without switching prisms, it provides sufficient performance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a polarizing prism according to the present invention. FIG. 2 is a graph showing the wavelength dependence of the viewing angle of the polarizing prism of the present invention, FIG. 3 is a cross-sectional view of the Ahrens prism, and FIG. 4 is a graph showing the wavelength dependence of the viewing angle of the Grand-Foucault prism. Figure 5 is a graph showing the wavelength dependence of the viewing angle of the Glan-Thompson prism. In Figure 6, the optical axis is Plinu°.
FIG. 2 is a diagram illustrating a polarizing prism located in a plane perpendicular to the cross section of the beam. 1.2-・Right triangular prism 3-・Scane triangular prism 4-・Air layer S+
, 82- Vertex angle of prism

Claims (1)

[Claims] An Ahrens prism composed of three triangular prisms, comprising one scalene triangular prism and two right-angled triangular prisms, each junction being formed by an air layer.Polarized light. prism.