# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DZffAldggyG
- **Gondola URL:** https://gondola.cc/posts/66591648-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/beb59e3e58.jpg
- **Posted:** 2026-06-12T16:09:51.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

You’re looking at a photograph sealed inside a solid block of glass: no entry wound, no surface scratch, just an image suspended in the middle of a flawless cube. The method is subsurface laser engraving, and it works by breaking the usual rule about where a laser is allowed to deposit its energy.

The medium, almost always optical-grade K9 crown glass, is transparent to the laser’s wavelength, so a beam aimed straight through it crosses the surface untouched. The trick is focus. A high numerical-aperture lens converges the beam to a point only microns wide deep inside the block. Along the entire path the irradiance stays harmless, but at that focal point it spikes into the gigawatt-per-square-centimetre range.

At that intensity glass stops behaving linearly:

	•	Multiphoton absorption lets several photons combine to bridge a bandgap no single photon could clear
	•	The freed electrons seed an avalanche that ionizes a microscopic plasma
	•	The plasma expands and cracks a void a few microns across, leaving one white scattering voxel

Pulse duration is everything. Nanosecond and femtosecond pulses dump their energy faster than heat can diffuse outward, so each fracture stays sharp and the surrounding glass never melts or clouds. Galvanometer mirrors and a moving stage then place hundreds of thousands of these voxels across a 3D grid, every one scattering ambient light, until a point-cloud image appears to hang in clear solid.

Acrylic can take the same treatment at lower pulse energies, since PMMA has a softer breakdown threshold, though it crazes more readily than glass. Either way the surface survives for one reason: only at the focus does intensity clear the damage threshold, so the material is wounded exactly where you aimed and nowhere else.

It is controlled, surgical optical damage: destruction precise enough to pass for magic.

#stemantics #lasers #photonics #materialscience #engineering

## Stats

- **Views:** 7,468
- **Likes:** 193
- **Shares:** 0
- **Comments:** 1

## Tags

engineering, lasers, materialscience, stemantics, photonics

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