Prism, a transparent object enclosed by intersecting but non parallel planes, used for splitting or dispersing light beams. Prisms are widely used in optical instruments. Prisms can be classified into several types based on their properties and applications. For example, in spectroscopic instruments, a "dispersive prism" that decomposes composite light into spectra is commonly used, such as an equilateral prism; The total reflection prism, which changes the direction of light in instruments such as periscopes and binoculars to adjust their imaging position, is generally used.

In the following figure, there is an example of a dispersive prism dividing white light into various monochromatic lights such as red, green, and blue

Reflective prisms are more widely used and can be seen in cameras, telescopes, microscopes, and various medical instruments. According to different structural forms, reflective prisms are further subdivided into various types of prisms,

Let's have a comprehensive understanding of the types of prism products

Common optical prisms

1. Right angle prism

The cross-section of a right angled prism is a right angled triangle, and the optical surface consists of two right angled faces and an inclined plane. Usually, a beam of light is incident from one right angled face, reflected by the inclined plane, and then bent 90 degrees before exiting from the other right angled face, as shown in the following figure

2. Ridge right angle prism

On the basis of a right angle prism, the inclined surface of the prism is divided into two faces and raised upwards to form the shape of a ridge. The two faces are perpendicular to each other, forming a ridge right angle prism. The optical path diagram of a right angled prism on the roof is shown below. The beam entering the prism will undergo a bending at the roof, swapping the left and right parts of the image before exiting.

3. Amish prism

Essentially, it is a truncated right angled prism, but with a ridge shaped section added to the slope. The most common function of this prism is to cut the image along the centerline and swap the left and right parts. The Amici prism is named after Italian astronomer Giovanni Amici, who invented it. It is an optical prism with dispersion function and is commonly used in spectrometers.

The Amish prism consists of two triangular prisms. The first prism is usually made of crown glass with moderate dispersion ability, while the second prism is made of high dispersion flint glass. When light enters the first prism, it is refracted first, then enters the interface between the two prisms, and finally exits in a direction almost perpendicular to the surface of the second prism.

4. Diagonal prism (refractive prism)

The cross-section of a diamond prism is in the shape of a parallelogram, with an acute angle of 45 degrees, so it can be seen as two right angled prisms bonded together. Its effect is to shift the incident beam by a certain distance before emitting it. One slope of the diamond prism can also be made in the form of a ridge,

5. Generalized diamond prism

A generalized rhombic prism is also a parallelogram in shape, but its acute angle is arbitrary. When light enters the prism, it undergoes a reflection before exiting,

When the prism rotates around the incident light, the direction of the emitted image does not rotate with the rotation of the prism, making it suitable for situations where the pupil distance is matched in ophthalmic instruments.

6. Double reflection prism

As a variation of the generalized diamond prism, the double reflection prism has two acute angles of different sizes, and the emission direction is determined by the size of the two acute angles, as shown in the following figure:

7. Paul's prism

The Paul prism is usually also an isosceles right angled triangular prism, but the beam of light enters from an oblique plane, reflects through two right angled surfaces, and then exits from the oblique plane to change the direction of the image. The Paul prism can also be made into a ridge structure on a right angled surface, thus forming a ridge Paul prism. The schematic diagram of a conventional Paul prism and a ridge Paul prism is shown below:

8. Dawei Prism

The Dawei prism is a type of rotator. After passing through this prism, the image is reversed by 180 degrees. In addition, when the prism is rotated around its optical axis, the rotation angle of the image is twice the rotation angle of the prism. Generally speaking, the Dawei prism uses the critical angle principle to achieve internal total reflection, so its field of view is limited. Meanwhile, it is important to keep the reflective surface clean and use parallel light.

9. Pentagonal prism

A pentagonal prism is a commonly used prism, with one angle being a right angle. The light beam enters from the right angle surface, undergoes two reflections internally, and exits from the other right angle surface. The outgoing light is at a 90 degree angle to the incident light. The optical path diagram and physical image are shown below:

Conclusion

In this article, we have summarized the types of optical prisms. According to their different functions, optical prisms can be divided into two categories: dispersive prisms and reflective prisms. The article introduces nine common optical prism units, including right angle prisms, diamond prisms, Paul prisms, and pentagonal prisms. It is worth noting that when using these prism units, the light beam is incident perpendicular to the surface, so the dispersion and aberration caused by the prism itself can be ignored. Through reading this article, everyone has a clear understanding of the structural forms of these prisms,