The Creation of a Hologram
The laser emits a single
wavelength, that is, coherent light. Coherent light waves travel in phase
with each other, the crest of one wave aligns with the crest of another.
Try to shine conventional white light on an object to make a hologram and
it simply will not work. That is because white light scatters too much.
If we were to simply illuminate our object with laser light and take a photograph, we would still only be recording the different light intensities of the object; we would not have captured any information about the phase of the light waves after bouncing off the object.
So, to capture this vital information, we need a standard or reference; we need a standard or a reference source in order to record the phase difference of the light waves and thus capture the information which supplies the vital dimensions and depth, to the holographic presentation. This standard we call a reference beam and the laser light itself supplies it.
The reference light is emitted in what we will call a plane wave. By enlisting the aid of a beam splitter, or rather a Micheleson Interferometer,
we are able to form two beams. The reference beam is allowed to hit the film directly.
The other beam which we will refer to as the object beam; this beam is spread by a diverging lens directed and spreads the light out to capture the entire image. Up until the instant in time that the object beam strikes the object, it too is a plane wave. As soon as it hits the object it is changed, or modulated according to the physical characteristics and dimensions of the object. The light, which ultimately reaches the film plane after being reflected by the object, now deviates in intensity and in phase from the virtually unhampered reference beam. That difference is a function of the object. What once began as a plane wave is now bouncing off the object in a complex interference pattern.
Using a laser in order to have this added information about the object would do us no good if the reference and object beams were not allowed to interfere at the film plane. The simplest interference that could take place on the film would be between the reference beam and the object beam but with no object at all. So that actually you have simply two plane waves coming from different directions and interfering on the film. The hologram, that is, the medium that contains all the information, is nothing more that a high contrast, very fine grain, black and white photographic film. The interference pattern on the hologram simulates tiny mirrors facing different angles. When an illuminating light reflects off the mirrors, the three-dimensional image that you see is a hologram.
If we were to simply illuminate our object with laser light and take a photograph, we would still only be recording the different light intensities of the object; we would not have captured any information about the phase of the light waves after bouncing off the object.
So, to capture this vital information, we need a standard or reference; we need a standard or a reference source in order to record the phase difference of the light waves and thus capture the information which supplies the vital dimensions and depth, to the holographic presentation. This standard we call a reference beam and the laser light itself supplies it.
The reference light is emitted in what we will call a plane wave. By enlisting the aid of a beam splitter, or rather a Micheleson Interferometer,
we are able to form two beams. The reference beam is allowed to hit the film directly.
The other beam which we will refer to as the object beam; this beam is spread by a diverging lens directed and spreads the light out to capture the entire image. Up until the instant in time that the object beam strikes the object, it too is a plane wave. As soon as it hits the object it is changed, or modulated according to the physical characteristics and dimensions of the object. The light, which ultimately reaches the film plane after being reflected by the object, now deviates in intensity and in phase from the virtually unhampered reference beam. That difference is a function of the object. What once began as a plane wave is now bouncing off the object in a complex interference pattern.
Using a laser in order to have this added information about the object would do us no good if the reference and object beams were not allowed to interfere at the film plane. The simplest interference that could take place on the film would be between the reference beam and the object beam but with no object at all. So that actually you have simply two plane waves coming from different directions and interfering on the film. The hologram, that is, the medium that contains all the information, is nothing more that a high contrast, very fine grain, black and white photographic film. The interference pattern on the hologram simulates tiny mirrors facing different angles. When an illuminating light reflects off the mirrors, the three-dimensional image that you see is a hologram.