In the late 1800s, no one knew what light was. Everyone knew it behaved like a wave some of the time, but all waves need to travel through some propagation medium. This propagation medium was called the luminiferous aether and an attempt to detect and quantify this aether led to one of the coolest experimental setups of all time: the Michelson-Morely experiment. It was a huge interferometer mounted on a gigantic slab of marble floating in a pool of mercury. By rotating the interferometer, Michelson and Morely expected to see a small phase shift in the interferometer, both confirming the existence of a luminiferous aether and giving them how fast the Earth moved through this medium.
Of course, there was no phase shift, throwing physics into chaos for a few years. When [Beaglebreath] first learned about the Michelson-Morely interferometer he was amazed by the experimental setup. He’s built a few interferometers over the years, but for The Hackaday Prize, he’s making something useful out of one of these luminiferous aether detectors: a functional laser rangefinder capable of measuring distances of up to 60 inches with an error of 0.000005 inches.
The core of the system is an HP 5528A laser interferometer system. [Beaglebreath] has been collecting the individual components of this system off of eBay for several years now, and amazingly, he has all the parts. That’s dedication, right there. This laser interferometer system will be mounted to a simple camera slider, and with the interferometer measurements, humidity and temperature measurements, and some interesting code (running on one of these for hacker cred), [Beaglebreath] stands a good shot at measuring things very, very accurately.
The devil is in the details, and when you’re measuring things this precisely there are a lot of details. The original Michelson-Morely interferometer was affected by passing horse-drawn carriages and even distant lightning storms. While [Beaglebreath] isn’t using as long of a beam path as the OG interferometer, he’ll still have a lot of bugs to squash to bring this project to its full potential.
The project featured in this post is an entry in The Hackaday Prize. Build something awesome and win a trip to space or hundreds of other prizes.
The Hafele–Keating experiment was a test of the theory of relativity. In October 1971, Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four cesium-beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory. When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of special and general relativity.
Mispelled “Morley” twice.
Beside that, I would like to replicate the Michelson-Morley experiment some day.
What exactly would someone do with a device that measures so accurately over such a distance? Assuming they can get it to work that is. I can think of something, but I don’t want to give anyone else any ideas at this point.
At my last job as a CNC tech we used interferometers identical to his setup or newer to calibrate our Coordinate Measurement Machines (CMM), check surface flatness on the granite surface plates, and measure lead screw pitch error on the cnc machines. On the pitch error you can enter the offset into the control and the control will compensate to make sure it is where it is supposed to be.
There are also angular measurement heads for the interferometers as well, I would love to get ahold of one to check my harmonic drive on my telescope mount.
Gravitational wave detection. Two masses that twitch towards each other when the wave passes. Well, use three axes. He can get another 2 orders of magnitude by dithering one mirror position with a piezoelectric device – if the HP stuff doesn’t already do that. Search for Robert Forwards papers from Hughes Research about 1970 and his noise reduction and accuracy increasing methods for gravity wave detectors and his rotating gradiometer. I have have the originals if they are not on the interweb.
Its certainly an interesting idea for testing a theory again that was successfully tested that many years ago. Several years ago, the composer Glass wrote work called “Light” that celebrated the centenary of the experiment. Incidentally if HaD isn’t interested in the papers, well copies, then I personally would be interested in copies. That is if the search engines do not deliver.
The HP stuff DOES do that – if you disassemble the case, there is a piezo transducer on the rear mirror mount which (I believe) is controlled by the internal electronics. This particular laser head also emits two orthogonal polarizations as well. We have 4 of these systems (including one with a pair of AOMs for frequency shifting the two components for heterodyne interferometry).
This idea is certainly more than theory (as far as gravity wave detection goes): There are currently several active systems around the world used for astronomical research:
http://en.wikipedia.org/wiki/Virgo_interferometer
http://en.wikipedia.org/wiki/LIGO
http://www.aigo.org.au/
I have an old HP 5500C laser head. It uses a piezo transducer to tune to laser frequency, along with some other optics in the Laser head. I thought that was a cool idea, but Hewlett Packard stopped manufacturing the lasers that way. My newer 5517B uses an internal oven to heat the tube to make it expand to the right size.
I want to be able calibrate machinists shop floor measuring tools and their gage blocks and check rods. I also want to be able to calibrate granite surface plates and layout tables. I will also be able to measure if a milling machine’s XY tables are out of alignment.
I also have an idea for a measuring differential pressures in a u-tube manometer. The reference mirror would move as well as the moving mirror. The mirror surface would actually be the surface of the liquid in the u-tube.
You want to check a milling machine’s accuracy to five millionths of an inch do you? Good luck to you there. I guess you don’t send work out to be heat treated either.
I put together one of these a few years ago (HP laser interferometer setup) to measure the pitch error in the lead screws on a cnc milling machine I was building. Then I moved and it all ended up in a storage locker. Wa wah… I believe another original use for them was as a positional feedback device on a wafer stepper.
0.000005 inches is 127 nm for those (like me) confused by moon units.