Five differences between holographic photography and ordinary photography

Holography is a new photography technology, which records all the information (amplitude and phase) in the reflected or transmitted light wave of the object being photographed.

Ordinary photography uses the principle of lens imaging to record the surface image reflecting the change of light intensity on the surface of the object being photographed on the photosensitive film/device.

Holography not only records the intensity (amplitude) of the reflected light wave of the photographed object, but also records the phase of the reflected light wave. This can be achieved by superimposing the reference beam and the reflected beam on the photographic film to produce an interference pattern.

Both the reference beam and the reflected beam are separated from the laser beam with good coherence. The interferogram recorded on the photosensitive film/device contains complex interferogram with different transparency, which is called "hologram" and is equivalent to an irregular diffraction grating. The apparent image of the original object cannot be seen from the hologram, but when the laser beam with the same original reference beam passes through the hologram, two groups of diffracted light waves with the same original reflected light of the object will be generated, one group will diverge and the other group will converge. This effect of reconstructing the original light wave state is called "wavefront reconstruction". From these two groups of diffracted light waves, we can get two images with the same stereoscopic effect as the original: one is a virtual image, which is located in the position of the original; The other is the conjugate real image, which is located on the other side of the hologram. Holography has many applications in information storage, deformation measurement and optical information processing.

In addition, it is also possible to use ultrasonic waves or microwaves instead of light waves to form corresponding holograms, which are called "ultrasonic holography" and "microwave holography".

Simply put, holography is a kind of photographic record that shows the stereoscopic effect through the cooperation of a group of auxiliary reference beams.