Optics ★★☆ Moderate New

🔮 Holography

Record a hologram by letting object and reference waves interfere on the recording plane, then reconstruct the virtual image by illuminating the hologram with the reference beam alone. Drag the object point to change the interference pattern.

Scene: reference + object waves
Hologram: interference pattern
λ = 532 nm (green)
Fringe spacing: —
Mode: Recording

How Holography Works

A hologram records not just the intensity of light but also its phase. This is achieved by splitting a coherent laser beam into two:

Reference beam — a plane wave that travels directly to the recording medium at a fixed angle θ_ref.
Object beam — light scattered from the object (simulated here as a point source) that also reaches the recording medium.

Where these waves meet, they create an interference pattern — a set of bright and dark fringes whose spacing depends on the wavelength λ and the angle between beams: d = λ / (2 sin(θ/2)).

Reconstruction: illuminate the developed hologram with only the reference beam. The interference fringes act as a diffraction grating that reproduces the original object wave — producing a virtual image behind the hologram and a real image in front.

Drag the sliders or click the scene canvas to move the object point.

About Holography Principles

Holography is the science of recording and reproducing complete optical wavefronts, capturing both the amplitude and phase of light scattered from a scene. Dennis Gabor conceived the idea in 1948 as a method to improve electron microscope resolution, but it was the invention of the laser in 1960 that enabled practical optical holography, for which Gabor received the Nobel Prize in Physics in 1971.

The physics relies on optical interference: the object wave and a coherent reference wave superpose on a recording medium, creating microscopic fringes whose spacing and contrast encode the phase and amplitude information at every point. Mathematical reconstruction via Fourier optics shows that illuminating the developed hologram with the reference wave diffracts light precisely to reproduce the original wavefront.

Modern holography spans a rich ecosystem: analogue silver-halide holograms for security labels, digital holographic microscopy for quantitative biology, holographic optical tweezers for manipulating single cells, wavelength-multiplexed holograms for colour 3D displays, and computational holographic projections for AR glasses. The field sits at the intersection of optics, information theory, and materials science.

Frequently Asked Questions

What property of laser light makes holography possible?

Holography requires coherent light — photons with a fixed phase relationship over time (temporal coherence) and across the beam (spatial coherence). Lasers provide both, allowing stable interference fringes to form during the exposure time. Ordinary white light has too short a coherence length.

What is the coherence length and why does it matter?

Coherence length is the maximum path-length difference between the reference and object beams over which interference fringes remain visible. It must exceed the depth of the scene being recorded. HeNe lasers have coherence lengths of tens of centimetres; diode lasers vary from millimetres to metres.

How are colour holograms made?

Full-colour holograms are recorded with three lasers at red, green, and blue wavelengths simultaneously. Each wavelength creates its own set of fringes at slightly different spacings; illuminating with the same three wavelengths reconstructs all three colour channels, combining to reproduce the original colours.

What is holographic interferometry?

Holographic interferometry compares two wavefronts recorded at different times or under different conditions. Any deformation or vibration of the object changes the optical path lengths, creating interference fringes in the reconstructed image that map displacements with nanometre precision.

What limits the resolution of a hologram?

Hologram resolution is limited by the grain size of the recording medium (typically 1–3 µm for high-resolution film), the coherence of the light source, and mechanical stability during exposure (vibrations larger than λ/4 wash out fringes). Digital holograms are additionally limited by the pixel pitch of the camera sensor.