Chapter 2 Two-Step Rainbow Holography [1]
The two-step rainbow hologram is a rainbow hologram obtained through two production steps. 2.1 The First Step: Making Master Holograms with Off-axis Holography
If a master hologram made by the above method is illuminated with a light beam conjugate with the reference light, a real image can be obtained. As shown in Figure 2.2, the direction of the curvature of this reality is the opposite of the object, so it is called a real image.
2.2 Second Step: Making a Rainbow Hologram by Adding a Slit In the reproduction optical path shown in Fig. 2.3, a horizontal slit is placed behind the master hologram W1. Because of the restriction of the light beam by the slit, the reproduced image is reproduced. This is produced by the diffracted light in the small area corresponding to the slit opening on W1 but still intact. The recording material W2 is placed near the twilight and overlaps with coherent reference light and light transmitted through W1 and the slit to form an interference field. Then W2 will record the wavefront of the real image so as to obtain a new hologram, i.e. a rainbow hologram W2.
If the rainbow hologram W2 is illuminated with the conjugated reference light R1*, an artifact, ie, a normal object, is produced.
Since a slit is added during the production process, a monochrome image can be reproduced under white light conditions. If the wavelength of the illumination light beam is the same as the wavelength at the time of recording, when the observer's eyes are placed on the opening of the slit image to observe the object image, only the object image with the same wavelength as that used when the object is recorded can be seen. It is not visible outside the slit. If the rainbow hologram is illuminated with white light, each set of wavelengths of light forms a set of slit images and object images, which appear in different spatial locations. If the observer moves his or her gaze up and down near the slit, he or she can see objects of different colors from red to purple. Only one color image can be seen through a slit. This series of objects of different colors resembles a rainbow, so it is called a rainbow hologram.
In order to achieve the effect of encryption and anti-counterfeiting, in the production of rainbow holograms, the optical path was improved, the lens was introduced, and the Fourier transform of the lens was used to intelligently record the darkened spectrum used for encryption in a position on the rainbow hologram. , to achieve the effect of encryption security.
In order to achieve the effect of encryption and anti-counterfeiting, in the production of rainbow holograms, the optical path was improved, the lens was introduced, and the Fourier transform of the lens was used to intelligently record the darkened spectrum used for encryption in a position on the rainbow hologram. , to achieve the effect of encryption security.