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🔬Modern Optics

🔬modern optics review

9.4 Digital holography and computer-generated holograms

3 min readLast Updated on July 22, 2024

Digital holography revolutionizes traditional techniques by using digital sensors and algorithms to record and reconstruct holograms. This enables flexible post-processing, quantitative phase imaging, and precise measurements, opening up new possibilities in microscopy and metrology.

Computer-generated holograms take it a step further, using numerical simulations to design custom wavefronts. These can be displayed on spatial light modulators, creating dynamic holograms for applications like 3D displays and augmented reality.

Digital Holography and Computer-Generated Holograms

Principles of digital holography

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  • Digital holography records and reconstructs holograms using digital sensors and numerical reconstruction algorithms
    • Replaces traditional photographic film with digital cameras or sensors for recording holograms
    • Employs numerical reconstruction algorithms to simulate the optical reconstruction process digitally
  • Basic setup for digital holography includes a coherent light source (laser), beam splitter to divide light into object and reference beams, digital sensor to record interference pattern, and computer to store and process recorded data
  • Recorded digital hologram contains both amplitude and phase information of object wave
    • Enables numerical focusing and reconstruction of object at different depths by manipulating recorded data
  • Enables quantitative phase imaging by capturing phase information
    • Measures optical path length differences and surface topography using phase data (interferometry)

Computer-generated hologram techniques

  • Computer-generated holograms (CGHs) are created using numerical algorithms and simulations to design arbitrary wavefronts and light distributions
  • Fourier transform serves as fundamental tool in generating CGHs
    • Complex amplitude of desired wavefront is Fourier transformed to obtain hologram pattern
    • Inverse Fourier transform of hologram reconstructs desired wavefront
  • Iterative algorithms like Gerchberg-Saxton algorithm optimize CGHs by iteratively refining hologram to minimize difference between desired and reconstructed wavefronts
  • CGHs can be displayed on spatial light modulators (SLMs) to physically reconstruct designed wavefront
    • SLMs modulate phase or amplitude of incident light based on CGH pattern (liquid crystal displays, digital micromirror devices)

Digital vs traditional holography

  • Advantages of digital holography:
    • Eliminates need for photographic film processing by recording and reconstructing holograms digitally
    • Enables flexible post-processing and analysis through numerical focusing and reconstruction
    • Allows precise measurements of surface topography and optical path length differences via quantitative phase imaging
    • Facilitates easier storage, transmission, and manipulation of digital holograms compared to physical holograms
  • Limitations of digital holography:
    • Suffers from limited resolution due to pixel size and number of digital sensor (megapixels)
    • Demands high computational power for numerical reconstruction and processing (graphics processing units)
    • Susceptible to noise and artifacts introduced by digital sensor and numerical algorithms (quantization noise, speckle noise)
    • Requires specialized and expensive equipment such as high-resolution cameras and powerful computers

Applications in microscopy and metrology

  • Digital holographic microscopy (DHM) enables quantitative phase imaging of biological samples and microstructures
    • Provides label-free, non-invasive, and real-time imaging of living cells and tissues (cell culture monitoring)
    • Allows numerical refocusing and reconstruction of 3D object volumes (tomography)
  • Metrology and surface characterization applications measure surface topography and deformations with nanometer-scale precision using digital holography
    • Useful for quality control, material characterization, and non-destructive testing (semiconductor wafer inspection, MEMS characterization)
  • Virtual and augmented reality applications use CGHs to create realistic 3D displays and holograms
    • Generates complex, dynamic, and interactive 3D scenes for gaming, education, training, and visualization (holographic displays, head-up displays)


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AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.