My TECH Definitions
Holography: The practice of creating and permanently recording three dimensional images. Sometimes referred to as optical holography.
Hologram: A three dimensional image which is optically and permanently recorded, in a light sensitive recording material such as film, using laser light (coherent light). The hologram image is recreated, or played back, via illumination by laser light or a point source of white light at a predetermined angle of illumination. There are more technical definitions available on the internet for those wanting a more scientific definition.
Sort of, Technically speaking: The coherent laser light directed at and then reflecting from the object or scene, illuminates the recording material, and the coherent light from another beam, the reference beam, also illuminates the recording material as well and together they create a microscopic pattern in the recording medium, called interference fringes. It is this microscopic interference pattern that records the properties of light that recreate fully three dimensional images and other optical phenomena.
Parts of a Holographic Image:
The actual surface of the recording film is called the Image plane.
Holograms may display virtual, real, and pseudo-scopic images.
-Virtual images appear to be behind the image plane film surface.
-Real images appear to be partially or completely out in front of the image plane film surface.
-Pseudo-scopic images are a type of real image. Pseudo-scopic images appear to be upside down and inside out.
This is a difficult idea to visualize without seeing the holograms.
Creating an analog hologram: Optical recording components such as a laser, mirrors and lenses are set up on a stable work surface, which isolates the recording system from vibrations. These components guide the light from the laser, to both illuminate the scene, referred to as the object beam(s) and to create an additional required beam, the reference beam, that also illuminates the recording material.
Holography recording materials: These are high resolution, light sensitive, films, and emulsions. The most common materials are silver halide films, photo polymer, and dichromate gel, which are formulated specifically for recording holograms at a particular wavelength. There are also panchromatic films which are capable of recording holograms with multiple wavelength laser light. Some recording materials require a darkroom for chemical development of the hologram and these need to be designed with safety in mind with proper ventilation and personal protective equipment as required. There are some recording materials, like Photo Polymer, that do not require chemical processing.
Holography Recording Studios/Labs and Equipment
There are many types of recording studios, sometimes referred to as labs. These can be home made or cost a small fortune. Holography studios should be isolated from vibrations which can destroy the recording.
Types of Studios
One beam or Single Beam holograms can be created with minimal optics in a quiet, but not necessarily optically stable (isolated) environment. There are starter hologram kits on the market which supply basic components for beginning one beam set ups. These can be valuable learning tools and students will often use these initially and then build their own more robust systems. Component holders can be built from angle aluminum and other materials available at local hardware stores. The images shown below, show the few optics required to create holograms using a minimum of equipment, which I built for teaching and making holograms. This simple, one beam set up shown below recorded the hologram Ribbon 2019, shown next to it.
An inexpensive Sand Isolation Table, originated by Jerry Pethick and Lloyd Cross, can be built from ordinary materials. PVC pipe components are used for holding optics. There are many examples of this type of system and instructions for building these. One beam and multiple beam holograms can be created using this inexpensive system. Shown here is one of 3 such systems I built for teaching holography at the Evergreen State College in the 1980's. Several different types of holograms can be made using this inexpensive system. Many artists learned on sand tables and some went on to create elaborate images using these sand table isolation systems.
High end (expensive) Isolation Tables are systems that are considered for professional applications. The isolation tables are mostly industrial made and most have a steel surface. These can be small or quite large, sometimes up to 20 x 20’ in size. People have made tables out of poured concrete as well. Either version usually end up weighing 3000 lbs. or more and so structural concerns must be taken into consideration. Steel top tables allow optical components to be mounted on magnetic bases, facilitating a very flexible system for setting up the optics. I have had the opportunity to design labs with such tables and systems. Two are shown below. On the left is the physics lab holography table at the Evergreen College, the center image is the Global Images Holographic Studio I designed and on the right is the Ledalite Architectural Products Research facility lab, which I designed.
There are basic essential optical components required for making holograms. The key component is a LASER, suitable for holography. The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Not all lasers are the same and some are not designed for recording holograms. Basically, there are gas lasers, diode lasers, and pulse lasers used for holography. Hologram recording lasers are also specified as TEM00 mode. In general, a holography Laser will emit light of a particular color, or wavelength, within the visible spectrum. For instance, a gas, HeNe, helium neon laser emits red light at a wavelength of 632 nanometers.
The laser light must be directed, and sometimes it is split into multiple beams. The light needs to be expanded and cleaned up a bit for a nice recording. The optics required, should be sourced from a reputable dealer. To direct the laser light within the recording area, the light is reflected off one or more front surface mirrors. For multiple beam set ups, a beam splitter is required to create two or more beams. The beam(s) then must be expanded with a lens, to illuminate the object or scene, (object beam) and fully illuminate the recording material, (reference beam) . Advanced set ups also use an optical component called a Spatial Filter. This is a special component that holds a microscope objective lens and a pin hole component that helps to clean up the beam. For advanced recordings, it’s a good idea to have a light meter as well and there are some phone apps for this. The images above, show assortment of optical components, red light from a HeNe laser and blue light from a HeCad laser.