Laser diode self-mixing: Range-finding and sub-micron vibration measurement
Why Hacker News recommends it
HN points to it as a cool demonstration of cheap precision laser measurement and the origin of hacks based on self-mixing.
What it is
Ben Krasnow of Applied Science shows that a plain laser diode can measure sub-micron vibrations from centimeters away using self-mixing interferometry, and can also be used for range-finding.
Recommended by 1 HN commenters across 1 different months, 2019 to 2025.
What Hacker News said
Recommends birktj · 2024-08 · on “Open source laser microphone picks up laptop keystrokes”
Related to this Applied Science on YouTube has a pretty cool video where he demonstrates how a single laser diode can be used to measure miniscule vibrations. I wonder if this would be sufficient for a laser microphone? [this video]
Cites colechristensen · 2019-07 · on “Kern Microtechnik: Accurate CNC Machines [video]”
There is a cool effect where a laser reflecting back into itself will cause interference inside the laser diode and affect the power required to drive it in a measurable way and with it you can extract a surprising amount of information (distance, rotation, angle, speed, etc.) I was ... hasty ... with my first laser diode and burned it out in about 30 seconds. I like to tell myself the money wasted was spent on learning lessons. The second is coming in the mail. The upshot with this method is that it can be extremely low cost and give you access to write code that interfaces directly with physics instead of somebody else's device. The idea for hacking on these things comes from Ben Krasnow [
Cites amelius · 2025-09 · on “Lidar, optical distance and time of flight sensors”
Slightly offtopic, why is it so difficult to find a cheap and compact laser interferometer that can do sub-micron measurements? This guy gets close: [this video] But why isn't something cheap and small like this commercially available as an integrated system?