Demystifying the Terminology of Holography — part 1: Recording and reconstructing a hologram

Holography, the science and art of creating three-dimensional (3D) images, has fascinated people for decades. As holography continues to evolve and find new applications in various industries, it’s important to have a solid understanding of the terminology associated with this fascinating field. In this article, we will delve into the key terms used in holography, demystifying the language and providing a comprehensive guide to help you navigate this captivating realm.

Before we start, keep in mind the following image, which depicts the process of recording a hologram.

Figure 1. Recording a hologram by Bob Mellish

Hologram: A hologram refers to the recorded interference pattern produced by the interaction of light waves. It is a 3D representation of an object or scene that possesses the ability to reconstruct a full parallax view when illuminated with coherent light. Holograms capture both the amplitude and phase information of light, resulting in vivid, lifelike images. The phase information contain the information regarding depth and hence, shape of the 3D object.

Coherent Light: Coherent light consists of waves that are in phase with each other, meaning they have the same frequency, wavelength, and direction of propagation. Laser light is commonly used as a source of coherent light in holography due to its monochromaticity and low divergence.

Interference: Interference occurs when two or more light waves superimpose, resulting in constructive or destructive interference patterns. In holography, interference is crucial as it enables the encoding and decoding of information necessary to recreate a 3D image.

Object Beam: The object beam in holography refers to the beam of light that illuminates the object being recorded. This beam interacts with the reference beam to create an interference pattern that is recorded on a holographic medium.

Reference Beam: The reference beam is a separate beam of coherent light that is used as a reference to interfere with the object beam. It provides the necessary reference wavefront against which the object wavefront is compared to create the interference pattern.

Holographic Plate/Film: A holographic plate or film is a photosensitive medium used for recording and storing holograms. It consists of a thin layer that reacts to the intensity and phase of the interfering light waves, capturing the interference pattern for later reconstruction.

Reconstruction: Reconstruction is the process of illuminating a recorded hologram with coherent light, which re-creates the original object wavefront and generates a virtual or real image of the object. This process involves diffraction and interference, resulting in a 3D representation that can be viewed from different angles. The process is shown in Fig. 2.

Figure 2. Reconstructing a hologram by Bob Mellish

Conclusion

As holography continues to captivate our imaginations and find new applications in fields such as entertainment, education, and healthcare, understanding the terminology associated with this fascinating technology becomes increasingly important. This comprehensive guide has provided an overview of key terms used in holography, shedding light on the language and concepts that underpin this extraordinary field. By familiarizing ourselves with these terms, we can delve deeper into the world of holography, appreciating its intricacies and unlocking its endless creative possibilities.