diffraction

13 Articles

A mirrorless camera is mounted on a stand, facing downwards toward a rotating microscope stage made of wood. A pair of wires come down from the stage, and a man's hand is pointing to the stage.

Building A Microscope Without Lenses

December 4, 2025 by 7 Comments

It’s relatively easy to understand how optical microscopes work at low magnifications: one lens magnifies an image, the next magnifies the already-magnified image, and so on until it reaches the eye or sensor. At high magnifications, however, that model starts to fail when the feature size of the specimen nears the optical system’s diffraction limit. In a recent video, [xoreaxeax] built a simple microscope, then designed another microscope to overcome the diffraction limit without lenses or mirrors (the video is in German, but with automatic English subtitles).

The first part of the video goes over how lenses work and how they can be combined to magnify images. The first microscope was made out of camera lenses, and could resolve onion cells. The shorter the focal length of the objective lens, the stronger the magnification is, and a spherical lens gives the shortest focal length. [xoreaxeax] therefore made one by melting a bit of soda-lime glass with a torch. The picture it gave was indistinct, but highly magnified. Continue reading “Building A Microscope Without Lenses” →

An array of tiny parallel green lines appears over a steel surface. The white dot a laser beam is visible in the lower center of the picture.

A New Way To Make (Almost) Holograms With Lasers

October 17, 2025 by 6 Comments

The spectrum of laser technologies available to hackers has gradually widened from basic gas lasers through CO2 tubes, diode lasers, and now fiber lasers. One of the newer entries is the MOPA laser, which combines a laser diode with a fiber-based light amplifier. The diode’s pulse length and repetition rate are easy to control, while the fiber amplifier gives it enough power to do interesting things – including, as [Ben Krasnow] found, etch hologram-like diffraction gratings onto stainless steel.

Stainless steel works because it forms a thin oxide layer when heated, with a thickness determined by the temperature it reaches. The oxide layer creates thin-film interference with incoming light, letting the laser mark parts of a steel sheet with different colors by varying the intensity of heating. [Ben] wrote a script to etch color images onto steel using this method, and noticed in one experiment that one area seemed to produce diffraction patterns. More experimentation revealed that the laser could consistently make diffraction gratings out of parallel patterns of oxide lines. Surprisingly, the oxide layer seemed to grow mostly down into the metal, instead of up from the surface.

The pitch of the grating is perpendicular to the direction of the etched lines, and varying the line spacing changes the angle of diffraction, which should in theory be enough control to print a hologram with the laser. [Ben]’s first experiment in this general direction was to create a script that turned black-and-white photographs into shimmering matrices of diffraction-grating pixels, in which each pixel’s grating orientation was determined by its brightness. To add a parallax depth effect, [Ben] spread out images into a gradient in a diffraction grating, so that it produced different images at different angles. The images were somewhat limited by the minimum size required for the grating pixels, but the effect was quite noticeable.

Unfortunately, since the oxide layers grow down into the metal, [Ben] doubts whether the laser can etch molds for diffraction-grating chocolate. If you’re interested in more diffraction optics, check out these custom diffraction lenses or the workings of normal holograms.

Double-Slit Time Diffraction At Optical Frequencies

October 18, 2024 by 11 Comments

The double-slit experiment, first performed by [Thomas Young] in 1801 provided the first definitive proof of the dual wave-particle nature of photons. A similar experiment can be performed that shows diffraction at optical frequencies by changing the reflectivity of a film of indium-tin-oxide (ITO), as demonstrated in an April 2024 paper (preprint) by [Romain Tirole] et al. as published in Nature Physics. The reflectivity of a 40 nm thick film of ITO deposited on a glass surface is altered with 225 femtosecond pulses from a 230.2 THz (1300 nm) laser, creating temporal ‘slits’.