Illuminating the hologram with the reference wave or with...

Name: Problem 2, Chapter 10: Holography. A Practical Approach
Uploaded: 2020-12-01T03:48:29-08:00
Duration: 4 min 1 s
Channel: Khoobchandra Agrawal
Description: Illuminating the hologram with the reference wave or with the object wave reconstructs the object wave and the reference wave, respectively. What is the reason for the always observed low intensity of the reconstructed reference wave (Figs. 10.1 and 10.2)?

Illuminating the hologram with the reference wave or with the object wave reconstructs the object wave and the reference wave, respectively. What is the reason for the always observed low intensity of the reconstructed reference wave (Figs. 10.1 and 10.2)?

Key Concepts

Holography

Holography involves recording and reconstructing complete wavefronts that include both amplitude and phase information. A hologram records the interference pattern created when a coherent object wave and a coherent reference wave overlap, and upon illumination, this pattern diffracts light to reproduce the original wavefronts.

Interference Pattern Recording

The interference pattern in a hologram is produced by the superposition of the object and reference waves. The resulting fringe pattern encodes the spatial phase variations of the object wave, but the modulation recorded is usually weak. This weak modulation is crucial because it determines how much of the incident light is effectively diffracted into the various reconstruction orders.

Diffraction Efficiency

Diffraction efficiency refers to the fraction of the incident light that is redirected into the desired diffracted order during holographic reconstruction. In typical holograms, particularly those with weak modulation, only a small portion of light is diffracted into the reconstructed wave. This low efficiency explains why the reconstructed reference wave always appears weak compared to the unmodulated light that passes directly through the hologram.

Energy Distribution in Reconstruction

During the reconstruction process, the incident illumination interacts with both the recorded modulation and the unmodulated parts of the hologram. Because the recorded interference pattern represents only a small modulation, most of the light remains undiffracted. Thus, the energy available for reconstructing the reference wave is inherently low, making its intensity weak in comparison to the object wave reconstruction.

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