How Holograms Work: A Guide to the Science and Technology of 3D Imaging

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How Holograms Work: A Guide To The Science And Technology Of 3D Imaging

Sophia Xu
Updated: September. 15, 2023 

Have you ever wondered how holograms work? How can a flat surface display a three-dimensional image that looks like it’s floating in the air? How can you see different perspectives of the image as you move around it? In this blogpost, we will explain the science and technology behind holograms, and show you some examples of how they are used in various fields and applications.

What is a hologram?

A hologram is a photographic recording of a light field, rather than an image formed by a lens. The light field is the pattern of light waves that reflects from an object and reaches our eyes. When we look at an object, we perceive its shape, color, texture, and depth based on the information carried by the light field.

A hologram captures the light field of an object using a technique called holography. Holography is a process that involves splitting a laser beam into two beams: one that illuminates the object (called the object beam), and one that acts as a reference (called the reference beam). The two beams interfere with each other and create a complex pattern of bright and dark spots on a photosensitive material (called the holographic medium). This pattern is called the interference pattern or the hologram.

The hologram contains all the information about the light field of the object, including its amplitude and phase. The amplitude is the brightness of the light, and the phase is the relative position of the light waves. By recording both amplitude and phase, the hologram preserves the three-dimensional information of the object.

To view the hologram, another laser beam (called the reconstruction beam) is shone onto it. The reconstruction beam interacts with the interference pattern and reconstructs the original light field of the object. The reconstructed light field then reaches our eyes or a camera, and we see a virtual image of the object that appears to be in front of or behind the hologram. The virtual image has all the properties of the real object, such as color, texture, and depth. We can also see different perspectives of the image as we move around it, just like we would see if the object was actually there.

What are the types of holograms?

There are different types of holograms based on how they are recorded and viewed. Some of the most common types are:

• Transmission holograms: These are holograms that are recorded and viewed using laser beams that pass through the holographic medium. The object beam and the reference beam are both directed from behind the medium, and they interfere on its front surface. The reconstruction beam is also directed from behind the medium, and it passes through it to form the virtual image on its front side. Transmission holograms can produce very high-quality images, but they require coherent laser light for both recording and viewing.

• Reflection holograms: These are holograms that are recorded and viewed using laser beams that reflect off the holographic medium. The object beam and the reference beam are both directed from in front of the medium, and they interfere on its back surface. The reconstruction beam is also directed from in front of the medium, and it reflects off it to form the virtual image on its back side. Reflection holograms can be viewed with white light sources, such as sunlight or lamps, but they have lower resolution and contrast than transmission holograms.

• Rainbow holograms: These are holograms that are recorded using laser beams, but viewed using white light sources. They are a special type of reflection holograms that use a technique called slit aperture to filter out different colors of light. The slit aperture is a narrow opening that is placed between the object and the holographic medium during recording. The slit aperture allows only a thin slice of light to reach each point on the medium, creating a vertical rainbow effect. During viewing, white light reflects off the medium and passes through the slit aperture again, reconstructing only one color for each viewing angle. Rainbow holograms can produce colorful images that can be seen from different angles, but they sacrifice some depth and detail.

• Computer-generated holograms: These are holograms that are not recorded from real objects, but created by computers using mathematical algorithms. Computer-generated holograms can simulate any kind of light field, including those that are impossible or impractical to produce with physical objects. They can also be modified or enhanced digitally before printing them on a holographic medium. Computer-generated holograms can have various applications, such as security, art, entertainment, education, and medicine.

What are some examples of holograms?

Holograms have many uses in various fields and applications. Some examples are

• Holographic displays: These are devices that can project holograms in mid-air, creating a realistic and immersive visual experience. Holographic displays can be used for entertainment, advertising, education, and communication. For example, holographic displays can create virtual characters, scenes, or objects that can interact with the viewers or the environment. They can also display information or data in a three-dimensional and intuitive way.

• Holographic storage: This is a technology that can store large amounts of data on a holographic medium, such as a disc or a crystal. Holographic storage can use multiple layers and angles of the medium to record and access data, increasing the storage capacity and speed. Holographic storage can also be more durable and secure than conventional storage methods. For example, holographic storage can store medical records, legal documents, or multimedia files.

• Holographic microscopy: This is a technique that can capture the three-dimensional structure and motion of microscopic objects, such as cells, bacteria, or viruses. Holographic microscopy can use a single beam of light to illuminate and record the object, without the need for lenses or filters. Holographic microscopy can also reconstruct the object in different focal planes, allowing for high-resolution and depth-resolved imaging. For example, holographic microscopy can be used for biological research, medical diagnosis, or drug development.

• Holographic interferometry: This is a method that can measure the deformation or displacement of an object due to stress, strain, temperature, pressure, or other factors. Holographic interferometry can use two holograms of the same object: one before and one after the deformation. By comparing the two holograms, the changes in the object can be detected and quantified. Holographic interferometry can also use multiple wavelengths of light to measure different properties of the object. For example, holographic interferometry can be used for engineering testing, quality control, or material analysis.

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I hope this blogpost has given you some insight into how holograms work and what they can do. If you have any questions or comments, please feel free to leave them below. Thank you for reading!