Moving holograms

It is also feasible to measure both droplet size and velocity simultaneously with the holographic method. Such a measurement system has been developed by Murakami and Ishikawa. 65()l They used two pulse lasers of different wavelengths to record two holograms on two different films, separated by an appropriate time interval. The displacements of moving particles were measured on a superimposed picture of the two films to determine the velocities of the particles. 

Hologram interferometry using two observations. The number of fringes passing an object point when the point of observation is moved from A to B is equal to the number of hyperboloids passed by that object point between the two exposures. This number is also equal to the number of hyperboloids of 1.8 seen between A and B. The results of 1.8 and 2.6 and 3.4 are identical. 

Davies, E. A smart move for holograms. Chemistry World, May 2006, 54. 

This allows for decreasing the vibration that inevitably arises with the use of stepping motors for mechanical moving. The distance between the pixels determines the pixel density and hologram size. The optimal distance is considered equal to the pixel diameter. At smaller distances, pixels overlap, whereas at bigger distances, the pixel density decreases. A significant loss of the diffraction efficiency is observed in both cases. 

In 1968 electrical engineer Stephen Benton developed the rainbow hologram-as the observer moves his head, he sees the spectrum of color as in a rainbow. This type of hologram can also be viewed in white light. 

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