Sunday, September 25, 2016

Terahertz Femtophotography: Bringing you the ancient world’s latest news



By: Harry Sullivan
http://mastersofmedia.hum.uva.nl/blog/2016/09/22/terahertz-femtophotography-bringing-you-the-ancient-worlds-latest-news/

Earlier this week, reports started trickling through the web about a camera developed by the Camera Culture Group at the Massachusetts Institute of Technology. Sure, a camera coming out of a MIT lab sounds interesting, but how can it be as exciting as previous technological advancements?
In this case, reading the pages of a book through its cover is this camera’s party trick. MIT have reportedly started to test a terahertz camera that can, at the moment, recognise the first twenty pages of a closed book, and identify printed letters on the first nine of these pages. According to Barmak Heshmat, this technology can potentially “look into some antique books that [the New York Metropolitan Museum] don’t even want to touch” (MIT News 2016), not to mention allow such findings to be inevitably digitised and later accessed via your favourite search engine or library.
There is undoubtedly a lot of complex science behind this emerging technology, including combining the terahertz camera with femtophotography. TechCrunch succinctly described this as “a clever way of capturing certain types of imagery just trillionths of a second apart [that] lets extremely fine distinctions be made, such as whether a reflected image comes from one page or the next one a fraction of a millimeter down” (Coldewey). Essentially, the terahertz camera subjects the book to radiation, then femtophotography converts the radiation imagery into a much clearer picture.
Terahertz Femtophotography
Terahertz Femtophotography
In a world of PDF documents, stumbling across a piece of centuries-old literature may present a problem to a scholar with the right touch for a keyboard and mouse, but not the right touch for handling a crumbling artefact with any confidence.


Codex Manesse, 1340 AD
Gizmodo writer Andrew Liszewski notes that “the [MIT] researchers feel their system could be a fantastic tool for museums or other facilities who want to explore and catalog historical documents, without actually having to touch or open them, and risk damage” (Gizmodo 2016).
The potential for this technology to explore extremely fragile ancient media documents should be seen as only the start. Though the technology is ‘only’ able to detect the first twenty pages of a book at the moment, it could be used to detect the layers of a piece of art. More specifically, a very expensive piece of art being sold at an auction, or being analysed by an art fraud department.
Moreover, without immediately realising the technology’s full potential, I argue that this is a triumph in media ecology’. As Neil Postman explained in his 2000 keynote speech at the Inaugural Media Ecology Association Convention:
“We put the word “media” in the front of the word “ecology” to suggest that we were not simply interested in media, but in the ways in which the interaction between media and human beings give a culture its character and, one might say, help a culture to maintain symbolic balance.” (Postman 11)
In this instance, uncovering ancient media through the use of contemporary technology should be seen as a way of enriching our culture and broadening scholarly horizons.
Moving on to the debate surrounding ‘media activism’, the phrase may cause long Facebook comments and Twitter rants to spring to mind. However, terahertz femtophotography could unveil a more subtle type of activism: The discovery of ancient literature may not be a trending topic as popular as a riot, but the uncovering of such documents could provide social commentary that covers a timeframe far longer than any current political activity.
This is not to say that the contemporary brand of media and political activism through social media is any more or less worthy of the term ‘activism’, but it is my view that technology that discloses social commentary from any age can only be adding to ‘activism’ within a cultural context.
Technology that can potentially read an unopened book, or detect fraudulent artwork should be seen as an overly positive thing for historians and art collectors. However, drawing a parallel with the “natural environment” (Postman 11), literature and artwork clouded by thousands of years of guesswork may be seen as a part of nature itself — something that shouldn’t be altered. It is a very far-fetched idea that anyone would not want to read what has previously been unreadable, or find out that the ‘Mona Lisa’ on display in The Louvre is indeed a fake, but it is still an idea nonetheless.

Shamona Lisa
Finally, regarding the question of disclosure above, recent debates over privacy regulations on social media have also brought up this topic, and also the need for editors at influential technological companies. The notion of the researchers using terahertz femtophotography automatically becoming editors of this ancient media does in a sense agree with the above article’s argument that industry-specific professionals need to be a part of the editorial process. However, with certain books as much a part of the ancient world as some landscape features, every individual on the planet should have the right to see these newsworthy pages.
Reference List:
Coldewey, Devin. “Judge a Book through Its Cover with This Terahertz Camera Setup”. TechCrunch. 2016. 12 September 2016. <http://social.techcrunch.com/2016/09/09/judge-a-book-through-its-cover-with-this-terahertz-camera-setup>.
Hardest, Larry. “Judging a Book through Its Cover”. MIT News.  2016. 15 September 2016. <http://news.mit.edu/2016/computational-imaging-method-reads-closed-books-0909>.
Humphries, Courtney. ‘A Detailed Road Map of the Human Brain’. MIT Technology Review. 2014. 15 September 2016. <https://www.technologyreview.com/s/526501/brain-mapping/>.
Levin, Sam. ‘“Facebook Needs an Editor”: Media Experts Urge Change after Photo Dispute’. The Guardian. 2016. 11 September 2016. <https://www.theguardian.com/technology/2016/sep/10/facebook-news-media-editor-vietnam-photo-censorship>.
Liszewski, Andrew. “MIT Invented a Camera That Can Read Closed Books”. Gizmodo. 2016. 15 September 2016. <http://gizmodo.com/mit-invented-a-camera-that-can-read-closed-books-1786522492>.
Postman, Neil. “The Humanism of Media Ecology”. Proceedings of the Media Ecology Association 1 (2000): 10–16.

Media List:
Shamona Lisa. 2016. 14 September 2016. <https://nl.pinterest.com/pin/73042825178948203/>.
MIT. Terahertz Femtophotogrphy. 2016. 13 September 2016 <https://tctechcrunch2011.files.wordpress.com/2016/09/terahertzbook.gif>.
Codex Manesse. 1340. 

Saturday, September 24, 2016

Abstract-Dual-Wavelength Terahertz Metasurfaces with Independent Phase and Amplitude Control at Each Wavelength


http://www.nature.com/articles/srep34020

We have designed, fabricated and characterized dual-wavelength metasurfaces that function at two assigned terahertz wavelengths with independent phase and amplitude control at each wavelength. Specifically, we have designed a dual-wavelength achromatic metasurface-based deflector deflecting the incident wave to the same direction at two selected wavelengths, which has circumvented the critical limitation of strong wavelength dependence in the planar metasurface-based devices caused by the resonant nature of the plasmonic structures. As a proof of concept demonstration, the designed dual-wavelength achromatic deflector has been fabricated, and characterized experimentally. The numerical simulations, theoretical predictions, and experimental results agree very well with each other, demonstrating the property of independently manipulating the phase profiles at two wavelengths. Furthermore, another unique feature of the designed metasurface is that it can independently tailor both the phase and amplitude profiles at two wavelengths. This property has been numerically validated by engineering a metasurface-based device to simultaneously generate two diffraction orders at two desired wavelengths.

Friday, September 23, 2016

How terahertz radiation could help brands identify consumers in future


We catch up one of the latest emerging technologies, terahertz radiation, and its future application in recognising individuals

http://www.cmo.com.au/article/607397/how-terahertz-radiation-could-help-brands-identify-consumers-future/

Marketers have longed dreamed of being able to identify every one of their customers, regardless of how they are interacting.
It is a capability that digital technology has delivered in the online world, but as yet no method has proven effective for the vast majority of offline interactions. Facial and mobile device recognition have both yet to become sufficiently accurate to deliver a positive ID against a known identity in all situations.
But what if you could recognise a person by their own unique chemical signature?
It’s not a crazy as it sounds.
Data61 researcher, Ken Smart, has been investigating the uses of terahertz radiation for 15 years as a scanning and detection technology.
“It has the ability to penetrate opaque materials, such as packaging and things like that,” Smart says. “You can look for voids inside of materials, or you can look for corrosion under paint. And it has a high sensitivity to liquids, so you can tell the water content of the thing you are looking at.”
All of that makes terahertz scanners particularly adept at instantly detecting substances like pesticide on fruit. Smart says this is of huge value to the agricultural sector, where some traditional chemical tests might take up to 24 hours to deliver a result – an appalling delay for anyone wanting to sell perishable goods.

“If you can determine how much is there within minutes, you have an advantage,” Smart says.
The technology could also be used to detect counterfeit food, such as when expensive fish are substituted with cheaper ones in restaurants. It has also been used to scan beneath works of art to determine what might have been painted over, by identifying the individual pigments.
The terahertz radiation band sits between the millimetre radiation band, often used for full body scanners at airports, and the optical radiation band used by human eyes. It is a non-ionising form of radiation, meaning it is safer than some other scanning techniques, such as those that use x-rays.
That terahertz radiation is only now being considered for commercial applications is due to recent breakthroughs which have made it easier to create devices with the power profile needed to work with it.

“It’s easier now to make high power devices, so you get stronger penetration and it is easier to see different things,” Smart says. “As you go up in frequency the wavelength gets smaller so your resolution increases, and you can see finer detail that you can’t capture at lower frequencies.
“You get to see an almost-unique signature. The more refined a substance is, the more unique its signature is. But once you start combining substances it gets a little murkier to tease out which one is which.”
Smart says the power profile of terahertz scanners also make standoff testing difficult, with an effective range of ten metres.
“So when it gets beyond that you have atmospheric effects and all sorts of things working against you,” Smart says. “But as people work their way around some of these problems there can be solutions found.”

And while it can scan through cloth and paper, it can’t penetrate metallic objects.
Despite the possibilities, however, the murkiness and range issue mean it may be some time before shop owners are identifying visitors by their unique chemical signature.
“That’s in the future, quite a long way,” Smart says.

Abstract-Short pulse generation and mode control of broadband terahertz quantum cascade lasers



Dominic Bachmann, Markus Rösch, Martin J. Süess, Mattias Beck, Karl Unterrainer, Juraj Darmo, Jérôme Faist, and Giacomo Scalari

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-3-10-1087

Ultra-short pulses are an attractive way of expanding today’s terahertz time-domain systems toward frequencies above 2 THz, and moreover mode control enables reliable generation of terahertz frequency combs based on quantum cascade lasers. We report on a waveguide engineering technique that enables the generation of a bandwidth up to ~ THz ~ 1  and an ultra-short pulse length of 2.5 ps in injection-seeded terahertz quantum cascade lasers. The reported technique is able to control and fully suppress higher order lateral modes in broadband terahertz quantum cascade lasers by introducing side-absorbers to metal–metal waveguides. The side-absorbers consist of a top metallization setback with respect to the laser ridge and an additional lossy metal layer. In continuous wave operation, the side-absorbers lead to octave-spanning laser emission, ranging from 1.63 to 3.37 THz, exhibiting a 725 GHz wide flat top within a 10 dB intensity range, as well as frequency comb operation with a bandwidth of 442 GHz. Numerical and experimental studies have been performed to optimize the impact of the side-absorbers on the emission properties and to determine the required increase of waveguide losses. Furthermore, these studies have led to a better understanding of the pulse formation dynamics of injection-seeded quantum cascade lasers.
© 2016 Optical Society of America
Full Article  |  PDF Article

Thursday, September 22, 2016

Abstract-Terahertz and Far-Infrared Windows Opened at Dome A, Antarctica



The terahertz and far-infrared (FIR) band, from approximately 0.3 THz to 15 THz (1 mm to 20 micron), is important for astrophysics as the thermal radiation of much of the universe peaks at these wavelengths and many spectral lines that trace the cycle of interstellar matter also lie within this band. However, water vapor renders the terrestrial atmosphere opaque to this frequency band over nearly all of the Earth's surface. Early radiometric measurements below 1 THz at Dome A, the highest point of the cold and dry Antarctic ice sheet, suggest that it may offer the best possible access for ground-based astronomical observations in the terahertz and FIR band. To address uncertainty in radiative transfer modelling, we carried out measurements of atmospheric radiation from Dome A spanning the entire water vapor pure rotation band from 20 micron to 350 micron wavelength by a Fourier transform spectrometer. Our measurements expose atmospheric windows having significant transmission throughout this band. Furthermore, by combining our broadband spectra with auxiliary data on the atmospheric state over Dome A, we set new constraints on the spectral absorption of water vapor at upper tropospheric temperatures important for accurately modeling the terrestrial climate. In particular, we find that current spectral models significantly underestimate the H2O continuum absorption.