The new version of the whitepaper is available at: DOLPi_Polarimetric_Camera_D_Prutchi_2015_v3
A new, complete version of the whitepaper on DOLPi is available for download here: DOLPi_Polarimetric_Camera_D_Prutchi_2015_v2
This paper presents the development and construction of two low-cost polarimetric cameras based on the Raspberry Pi 2. “DOLPi-MECH” is a filter-wheel-type camera capable of performing full Stokes analysis, while the electro-optic based “DOLPi” camera performs full linear polarimetric analysis at higher frame rate. Complete Python code for polarimetric imaging is presented. Various applications for the cameras are described, especially its use for locating mines and unexploded ordinance in humanitarian demining operations.
The image that the liquid-crystal-panel-based DOLPi takes at “45 degrees” is not strictly that, which is why I state in the paper:
“Bossa Nova’s method is straightforward if laboratory optical-grade components are used. These are very expensive and out of reach for most private enthusiasts. However, I found through experimentation that a welding mask LCP and a polarizer sheet can also give very satisfactory results.”
In reality, the LCP driven half-way acts as a quarter-wave plate, and hence the strict interpretation of the analysis at this level is for circular polarization rather than linear polarization at 45 degrees.
I didn’t want to go into a thorough explanation of polarization optics to keep the project accessible, but based on my experiments, I’m convinced that DOLPi’s “45 degree image” indeed contains a dominant 45 degree component when observing linearly polarized light.
This weekend I decided to build a mechanical filter-wheel-based polarimetric camera to serve as a basis for comparison to the LCP_based DOLPi. This camera is much slower than the LCP-based DOLPi because of the mechanical switching of filters, but it provides the data necessary for complete Stokes imaging (including the fourth Stokes parameter describing circular polarization). The pictures that it produces are of excellent quality!
Sent: Monday, August 24, 2015 9:39 AM
Subject: Your Project is a Semifinalist in the 2015 Hackaday Prize!
Dear David Prutchi,
Congratulations! We think your DOLPi – RasPi Polarization Camera is awesome and you are one of our top 100 picks for the Hackaday Prize. You are advancing to the next round.
What happens now? We are announcing this in a short bit on Hackaday and this is a good time for you to tell everyone that your product is now in the running for a trip to space! Spaaaace!
Hi! DOLPi is a low-cost polarization camera based on the Raspberry Pi.
Like intensity and color, polarization is another property of a light wave.
Humans cannot sense polarization, but many animals like cuttlefish and insects have polarization-sensitive vision that they use for navigation, finding water, and detecting transparent prey.
This is DOLPi – it is completely self-contained and easy to build. In spite of its simplicity, it holds truly awesome power for the development of brand new scientific and commercial applications!
DOLPi – A Low-Cost RasPi-based Polarization Camera
A polarimetric imager to detect invisible pollutants, locate landmines, identify cancerous tissues, and maybe even observe cloaked UFOs!
The polarization of light carries interesting information about our visual environment of which we are usually unaware. Some animals have evolved the capability to see polarization as a distinct characteristic of light, and rely critically on this sense for navigation and survival. For example, many fish, amphibians, arthropods, and octopuses use polarization vision as a compass for navigation, to detect water surfaces, to enhance the detection of prey and predators, and probably also as a private means to communicate among each other.
While we have used technology to expand our vision beyond the limits of our ordinary wavelength and intensity sensitivities, the unintuitive nature of polarization has slowed down the development of practical applications for polarization imaging. Polarization cameras do exist, but at over $50,000, they are mostly research curiosities that have found very few practical uses outside the lab.
The DOLPi project aims to widely open the field of polarization imaging by constructing a very low cost polarization camera that can be used to research and develop game-changing applications across a wide range of fields – spanning all the way from environmental monitoring and medical diagnostics, to security and antiterrorism applications.
The DOLPi polarization camera is based on a standard Raspberry Pi 2 single-board computer and its dedicated 5MP camera. What makes the DOLPi unique is that the camera sits behind a software-controlled electro-optic polarization modulator, allowing the capture of images through an electronic polarization analyzer. The modulator itself is hacked from two low-cost auto-darkening welding mask filters ($9 each). In spite of its simplicity, DOLPi produces very high quality polarization images.
This is a first-of-its-kind project! I am not aware of any polarization imager ever presented as an enthusiast-level DIY project, yet it holds truly awesome disruptive power for the development of brand new scientific and commercial applications!
A complete description of this project in pdf format is available at: DOLPi_Polarimetric_Camera_D_Prutchi_2015_v2
Sphere Research is clearing out all the Philips PMT assemblies they have in stock to empty their expensive off-site rental storage space. While stock is available, you can order any PMT shown as a Philips Medical Systems assembly at the beginning of this page for only $25 +shipping:
Simply identify the deal as coming from DIY Physics when ordering (Note from diyPhysics.com: nothing in it for us except passing along some great info…).
All these tubes will be cleared out shortly so they can close down their over-priced off-site rental storage space. The offer is limited to stock on hand at the time of order. Sphere Research is happy to consolidate orders and help you minimize shipping costs wherever possible. They can take Visa, MasterCard and PayPal for orders. These are very high performance tubes and hard to find, but they are very awkward for them to store in the big factory boxes, so they have to go.
Javier De Elias Cantalapiedra from Madrid, Spain posted the YouTube video above to show the e/m measurement system that he put together based on the description in our book. His measurement system is based on Hoag’s method, and his nicely laid-out setup allowed him to obtain very nice results (4 to 6% error compared to the theoretical e/m).
Javier is an industrial engineer who works in the telecommunications industry. However, his passion is physics, which he pursues at a (very high) amateur level.
Thank you Javier for sharing!
If there were any quantum effects to be seen, I wasn’t paying attention… Dorith (Mrs. diyPhysics) and I were having too much fun!
Click here for photos of Day 1 in the G Force One zero-g airplane
Click here for photos of Day 2 in the G Force One zero-g airplane
For more information about Zero G go to http://www.gozerog.com/
I HAVE NO RELATION TO SELLER – Just passing along in case someone is interested.
eBay item number 271206242864:
“The EG&G (or Perkin Elmer) SPCM-AQR is a self-contained module which detects single photons of light over the wavelength range from 400 nm to 1060 nm and sensitivity which often outperforms PMTs. The option 13-FC indicates 180 micron diameter Si APD, Dark Count < 250cps and FC connector attached.
I obtained this detector in working order five years ago and have not used it since then. The detector comes with two unknown optical fiber cables (one end: FC, the other end: bare fiber) and a supply cable to which you need to give 5V. No manual included. The US sale only.”
One of my all-time favorite circuits is the the following DC-to-AC inverter (click diagram to enlarge) based on an old color TV flyback:
A very interesting article by Bernhard Wittmann, Sven Ramelow, Fabian Steinlechner, Nathan K Langford, Nicolas Brunner, Howard M Wiseman, Rupert Ursin,and Anton Zeilinger, entitled “Loophole-free Einstein–Podolsky–Rosen experiment via quantum steering” appeared in the Nature’s New Journal of Physics, Volume 14, May 2012.
This paper describes a Bell’s Inequality Violation experiment in which the “fair sampling” loophole has been closed. This loophole posits the possibility that classical – rather than quantum – effects could be responsible for measured correlations between entangled pairs of photons in a Bell’s Inequality Violation experiment. The paper’s abstract reads:
“Tests of the predictions of quantum mechanics for entangled systems have provided increasing evidence against local realistic theories. However, there remains the crucial challenge of simultaneously closing all major loopholes—the locality, freedom-of-choice and detection loopholes—in a single experiment. An important sub-class of local realistic theories can be tested with the concept of ‘steering’. The term ‘steering’ was introduced by Schrödinger in 1935 for the fact that entanglement would seem to allow an experimenter to remotely steer the state of a distant system as in the Einstein–Podolsky–Rosen (EPR) argument. Einstein called this ‘spooky action at a distance’. EPR-steering has recently been rigorously formulated as a quantum information task opening it up to new experimental tests. Here, we present the first loophole-free demonstration of EPR-steering by violating three-setting quadratic steering inequality, tested with polarization-entangled photons shared between two distant laboratories. Our experiment demonstrates this effect while simultaneously closing all loopholes: both the locality loophole and a specific form of the freedom-of-choice loophole are closed by having a large separation of the parties and using fast quantum random number generators, and the fair-sampling loophole is closed by having high overall detection efficiency. Thereby, we exclude—for the first time loophole-free—an important class of local realistic theories considered by EPR. Besides its foundational importance, loophole-free steering also allows the distribution of quantum entanglement secure event in the presence of an untrusted party.”