Hologram

**Holography** enables a *wavefront* (an imaginary surface representing corresponding points of a wave that vibrate in unison) to be recorded and later re-constructed, useful in generating 3d images. A **hologram** is made by superimposing a second wavefront on a wavefront of interest, thereby generating an interference pattern which is recorded on a physical medium. When only the second wavefront illuminates the interference pattern, it is diffracted to recreate the original wavefront. Holograms are computer-generated by modelling the two wavefronts and adding them together digitally.

Any type of wave can be used but lasers are the most common. The laser beam is split into an object beam and a reference beam. The object beam is expanded by passing it through a lens and used to illuminate the subject. The recording medium is located where this light, after being reflected or scattered by the subject, will strike it. The reference beam is expanded and made to shine directly on the medium, where it interacts with the light coming from the subject to create the desired interference pattern. The purpose of the reference beam is to provide the recording device with information such as background light, picture angle, and beam profile.

A **holographic display** uses lasers to create 3d images which are processed by a computer to compensate for variations in picture fidelity, and then sent to the display. The holographic television display was created in 2013. It captures subjects in 3d space, processes images by a PC graphics card and replicates it with a series of laser diodes. The produced image is fully 3d and can be viewed from all 360 degrees to gain spatial perspective.

Holograms are also used in **volumetric displays** which create 3d imagery via the emission, scattering, or relaying of illumination from well-defined regions in 3d space.

**Touchable holograms** can detect a user's touch by sensing movements in the air. The device then provides haptic feedback to the user by sending an ultrasonic air blast in return. A possible implementation for this technology would be interactive displays in public kiosks; because this type of display does not require a user to physically touch a screen, it ensures that bacteria and viruses do not get transmitted from person to person.

**Holographic storage** is used an an alternative for high-capacity data storage. It records information throughout the volume of the medium and is capable of recording multiple images in the same area using light at different angles. Whereas magnetic and optical data storage records information a bit at a time in a linear fashion, holographic storage is capable of recording and reading millions of bits in parallel, enabling data transfer rates greater than those attained by traditional optical storage.

Hard light or holography architecture can use projected force fields to create clothing, avatars, bridges, barriers and even cities.

Holography was invented in 1947 by physicist Dennis Gabor who won the Nobel Prize for his invention.

In Star Wars, the Jedi use holocrons and holographic crystals to store data about their history. They also had advancements in holographic technology, ranging from blue 3d images with scan lines and distortions where transmission is over light years, to full colour realistic images.

Holograms are used in the holodeck and Emergency Medical Hologram from *Star Trek*.

**Holodecks** were used by the Federation which ran sophisticated holographic programs in closed rooms where holograms were projected via photons being contained in force fields. As such they were interactive and haptic, and were installed aboard starships, space stations, and institutions for use in entertainment, training, and investigative purposes.

The Emergency Medical Hologram was a holographic simulation of a Human developed during the 2360s designed to provide short-term advanced assistance during emergencies in sickbay to the extent of literally replacing a starship's medical officer.

### News

* October 2021: Researchers at the University of Glasgow have developed a system for holograms using *aerohaptics*, where jets of air create the sensation of touch on the user's fingers, hands, and wrists. References: Here and here.
* MIT’s AI can make holograms in real-time.