Triple Laser Speckle

Laser speckle is a visual artifact that appears as a grainy, shimmering noise pattern when using lasers for image projection, such as in a 3-laser (RGB) projector. It’s a fundamental optical effect caused by the coherent nature of laser light.

What causes laser speckle?

Laser light is:

Highly coherent (waves are in phase)
Highly directional
Monochromatic

When this coherent light reflects off a rough surface (like a projection screen), each tiny point on the surface scatters the light in slightly different directions. These scattered waves interfere with each other:

Constructive interference → bright spots
Destructive interference → dark spots

The random pattern created is called: Speckle.

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Why is speckle noticeable in triple-laser projectors?

A 3-laser projector uses separate pure-red, pure-green, and pure-blue lasers. These have very narrow bandwidths (high coherence), which increases the likelihood and intensity of speckle.

Even though there are 3 colors, each one produces its own speckled pattern. The combined effect can look like:

Fine moving grain
“Twinkling” on flat colors
Texture or shimmer on solid backgrounds

It becomes more visible when:
Using high-gain or smooth screens
Viewing from closer distances
Bright images are displayed
Projector includes pure-laser (not phosphor) light sources

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What reduces speckle?

User/environmental:
Use a matte, low-gain screen
Avoid ALR screens that amplify coherent noise
Sit farther from the screen
Slightly defocus (not ideal, but reduces speckle)

In simple terms
Laser speckle is a shimmering grain effect caused by the interference of coherent laser light after it scatters off a surface. It’s a natural side effect of using true lasers and is stronger in RGB laser projectors.

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