The Breakthroughs of the year

2009 is coming to its end... and it is time to review the most important scientific contributions of the year.
For this reason the magazine Science has published a special issue with the top 10 breakthroughs of the year (according to Science). And the winners are...

1.- Ardipithecus ramidus. Ardi was an Ethiopian woman, 1.20 m tall... and who lived 4,4 million years ago! It is the most ancient hominid fossil ever found.
2.- Pulsars. Gamma rays Fermi NASA telescope has allowed to detect pulsars. The telescope was put in orbit in 2008, and providing a measurement that was a proof of the relativity theory has been its most important success so far.
3.- ABA receptors. Major advances in the knowledge of the structure of the drought hormone have been achieved during 2009.
4.- Monopoles. Two research group have achieved magnetic pertubations of monopoles from spin ices.
5.- Rapamycin. Rapamycin (a medicine used to prevent transplant rejection) can prolong mammal's life. The experiment was carried out in rats, that prolong their lives between 9% and 14%.
6.- Water in the moon. NASA announced on the 13th November that the Lcross spacecraft sensors had detected water vapour and ice in the moon.
7.- Genetic therapy. Advances in genetic therapy to treat blindness.
8.- Graphene. Latest research about the graphene properties has revealed that this material could replace silicon in chips.
9.- Hubble repair. Hubble repair mission prolonged its life and improved some features.
10.- X-ray laser. Since we reported in a post some months ago, SLAC laboratory started running the first X-ray laser.

And what is the most important discovery for you? Fill in the survey you can find on your right!

Also, you can also find a really interesting and comprehensive podcast about the 10 most popular stories of Science in 2009 (the transcript can be downloaded here).

PHD Comics: Laser in Use!

Dont worry. There are real lasers in our optic labs ;).
(click on the picture to enlarge it)

If you want to know how graduate students are living or how life in the lab really is then visit:

"Piled Higher and Deeper - Life (or the lack thereof) in Academia".

PHD Comics

A comic strip by Jorge Cham. In general every 2. or 3. day there is a new phd comic strip online and he hits absolutly the situation :)! Click here if you want to go directly to his most popular 200 comic strips! Enjoy!

p.s. have a visit in our optic labs!

Refractive Index Database

Who dont know this problem: you need something urgent but you have to spend two hours until you have found it. In optics, knowing the refractive index of a material at a certain wavelength could be such a problem. The long solution is to search a book or a paper which helps you to calculate the refractive index, the short solution...

...is going to RefractiveIndex.INFO



created and maintained by Mikhail Polyanskiy. The Database is very extensive and includes:

Crystals/ Metals/ Liquids/ Gases/ Glasses/ Optical Glasses/ Plastics/ Liquid Crystals and even Metamaterials.

Simple choose the material and enter the desired wavelength. But you can do more as only calculating the refractive index. You can choose too from the optical property caculator things like:

reflection coefficient/ Abbe number/ Brewster´s angle/ critical angle or chromatic dispersion.

Simple things, but it save a lot of time. Enjoy!

Modelling an artificial eye with a CCD camera: see how they see!

In September I attended the "IX Reunión Nacional de Óptica" (Spanish National Optics Meeting); one of the posters presented there by the Optics Group from Zaragoza (J. Ares, V. Collados, J. Arines and A. Sánchez-Cano) was "Adiestramiento de la refracción subjetiva con ojos simulados mediante cámaras web". In this communication, the authors reported a system based on a CCD camera to simulate an artificial eye that is used to teach optics and optometry.

Let's start by explaining how the eye works.

Figure 1: Scheme of the eye

In the image an schematic view of an eye is represented; in a very simple model, we can consider the eye as a system formed by a refractive surface, the cornea, and the lens. In a normal eye, the light is focused at the fovea and the image is well-defined. When a person suffers from myopia, light is focused before the fovea; when a person suffers from long-sight, image is formed after the fovea.

Now, how can it be modelled with a web camera? Well, basically the webcam is a CCD sensor with a lens. If we replace this lens by a 35mm focal length lens (typical value for a human eye) and a diaphragm (which will act as a pupil), we can build an artificial eye.

Once, the webcam is ready you can try how people see. Ask for example for a pair of glasses and place them immediately before the webcam. If the person who has lent you the glasses suffers from myopia, you will see a blurred image: this is how this person sees without glasses (or better said, the opposite to the way this person sees: it corresponds to the vision of a long-sighted person with the same gradation):

Figure 2: Pictures from the first row represent a near-sighted eye without (left) and with (right) glasses to correct the myopia. The second row corresponds to a normal eye (ie., the webcam) without (left) and with (right) the same lenses as used in the previous case.

Literature Search II: Keep you up in Research – the Virtual Journals and RSS Feeds!

We know how to search relevant papers but science is a very fast developing field, especially the optic communities. To keep up we have to know what is published but we can´t do every week an extensive literature search. The solution is very easy but still satisfying: virtual journals and RSS feeds!

A virtual journal presents an online collection of relevant papers from different journals published during the last week or month. In physics the virtual journals by the American Institute of Physics (AIP) and the American Physical Society (APS) are very good, covering 5 topical areas:

virtual journals

For optics it is called:

virtual journal of ultrafast science

But also the ones for quantum information and nanoscale science contain a lot of optic papers:
virtual journal of quantum information
virtual journal of nanoscale science & technology
The first two mentioned are updated every month, the nanoscale science even every week! But although virtual journals present a good overview about relevant and interesting papers for the community, papers relevant to our work are perhaps (or mostly) not published there. Hence, we have to find an additional way to search relevant papers for us… and RSS feeds will help us a lot.


RSS feeds stands for “Really Simple Syndication” and are placed on many web-pages today. They provide you with the newest articles, information and news on the web-page. You only have to click on the RSS logo and then you can create a folder in the favorite of your browser. Today, more convenient is to connect them directly to your email client or reader. All advanced clients or readers support them (if you don’t have one, search for thunderbird or google reader). Really powerful are RSS feeds if you combine them with word-filters of your email client/reader program! Using the keywords of your research, your email/ reader program collects directly all relevant papers out of hundreds of papers. You don’t have to check them all personally.

Enjoy the lecture ;)!

Very Short Pulses – from Attoseconds to Yoctoseconds!

Coincidentally I noticed a headline:

“Yoctosecond Photon Pulses from Quark-Gluon Plasmas ” [1]

Like many optic scientists I am working with femtosecond laser pulses (1fs=10^-15). Many comrades in my group are dealing with attoseconds (10^-18s). They generate them in high harmonic generation processes and can push them down to around 80as [2,3]! Near to the frontier of the zeptoseconds (10^-21s) scale. In 1as light can travel a distance of 3*10^-10m, which corresponds roughly to the length of three hydrogen atoms. Today, 80as are the limit because of physical reasons in the high harmonic generation process. But new methods are in progress to reach the zeptoseconds scale. Now, a group has proposed a method how to generated yoctoseconds; 1ys is 10^-24 seconds! They describe how high-energetic photon pulses down to the yoctosecond time scale can be produced in heavy-ion collisions, particularly during the formation of a quark-gluon plasma.
How to measure (and to produce them in reality!) and to characterize these yoctosecond pulses… future will know it. However, my comrades have enough to struggle with 80as ;).

[1] Phys. Rev. Lett. 103, 152301 (2009)
[2] Science Vol. 320, 1614
[3] Attoworld

Literature Search I: How to find Information concerning your Work!

Very essentially, often underestimated, most poorly done, about what am I talking? Of course of the literature search! The literature search is a very important and powerful tool and helps you to save a lot of time and performing good experiments. Three main purposes are behind a literature search:

1. Find information concerning your experiment achieved by other groups (part I).
2. Keep you up of the progress in your research field (part II).
3. Getting new ideas :) …

In this post I write about the first part, presenting some useful webpages for literature search. The second part follows end of the week (introducing the virtual journals).

Today, nearly all scientific information are online available in the internet. But the challenge is to find it! To do so, many search pages exist which are in parallel checking different databases about your request. Probably your university or institute offers such a search machine too. In science, probably the best search page is:

web of knowledge

The page is well done, user friendly and contains a lot of background information.
Another way (which I really like) is to search directly on the journal homepage. Every (good) journal has today a (advanced) search function. In Optics, most of the relevant articles are published in the journals of the “Optical Society of America” briefly OSA. The link to the journal page is:

Opticsinfobase

You can search on all journals or on specified ones. If you have found an interesting paper, have a look at its references and citings. They are often listed with titles and links to their PDFs. I am sure it contains a lot of interesting papers for you. With time you will notice an author who have several publications on the same field. Check their group homepage! Normally, their full publications list (even PDFs) is online.
An – unusual – approach is to search publications by google. Either by google, or its version for science:

scholar.google.com

It is not as good as the other possibilities, but I had already some nice surprises with scholar google.
Another exotic way but it is worth to mention it, is the:

arxiv server

Papers can there be pre-published before they are accepted or rejected by a journal. Some communities, like the quantum information one, are nearly publishing every article on this server too.
To complete the first part, I want to draw your attention to the:

Encyclopedia of Laser Physics and Technology

It is an open-access encyclopedia with around 570 articles, and it explains the physical principles and common techniques in laser technology.
At the end, please remember that every search machine is worthless if you use the wrong keywords. But with some training you will quickly learn the suitable ones ;).

Optics at the disco

Thinking about going out tonight...?

If so, you might be familiarized with the lights shown in the video.

Sometimes people seem to dance in slow motion, as in the minute 1'02 of the video; the lights responsible of this effect are called stroboscopic lights.

Smoke is also widely used at the disco to produce optical effects: light is slightly dispersed by it and coloured ray traces are easily observed (example: minute 1'14 of the video).

And do you like drinking tonic? If you ask for one at the disco, it can have this appereance:

Don't worry! You haven't asked for the wrong drink and neither have you become colour-blind... It happens because in some discos there are ultraviolet lights (emitting at around 365nm) which excites quinine, a substance contained in the tonic, and producing fluorescence.

Acknowledgments: the author would like to thank B. Hester (from University of Maryland Student Chapter) for her help with the tonic fluorescence.

Where is your Coffee Cup?

…because soon we have coffee break! And you don’t want to miss it this time…



If you have heard something about the taste, please make a comment ;). It seems that they enjoy their coffees and tea.

To heat the water they used a continuous wave Nd:YAG laser with a maximum power of 2.5kW at 1064nm. The wavelength is already in the near infrared range and therefore not visible to our eyes. This type of laser is very often used in industry for material processing. Unfortunately, I couldn’t find more information about this group, what they are mainly working. Looking around in their laboratory I guess it is not an optics group but probably an engineering group – working somehow on material processing.
Have you already asked yourself, why we see the laser beam even it should be invisible for our eyes? The reason is simple. The digital camera with the CCD sensor (Nobel Prize this year!) is sensitive at these wavelengths too. Normally, the camera blocks the near infrared and infrared spectral range by a filter. If you watch carefully the movie, you will notice that they change the camera to their research camera where they do not have such a filter (after 42 seconds). Hence, the laser light scattered by the water can be detected by this camera and we can see the laser light on the camera screen.

Photonic Crystal Fibers: the 2. Generation of Optical Fibers

(taken from Optics Express Vol. 15, pp 15365)


Charles K. Kao was awarded this year with the Nobel Prize for his fundamental contribution about optical fiber in 1966. Nowadays, applied in high speed data communication optical fibers have an enormous impact in public life. But, is this already everything from optical fibers? Definitely not! In 1996 the research group around Prof. Dr. Russell was able to create the first micro-structured optical fibers, later called photonic crystal fibers (PCF). Contrary to normal optical fibers which consist of a core surrounded by a cladding with a smaller refractive index for total internal reflection, a PCF doesn’t have a cladding in this sense but its core is periodically surrounded by several small “air tunnels” which acts like a cladding, and much more! This construction allows researcher to engineer different parameters of the fiber, like the zero dispersion wavelength (ZDW) and the single mode condition. In bulk silica the ZDW is approximately 1.3µm. Above 1.3µm the dispersion is positive and this wavelength regime is called anomalous regime because it allows new phenomena (solitons, supercontinuum) which are not possible in the normal dispersion regime (negative dispersion). Note, that the dispersion parameter D [ps/km*nm] is proportional to –B2, the group velocity dispersion. The design of photonic crystal fibers enables to shift down the ZDW to 600nm, thus in the working regime of Ti:Sa lasers (800nm). Doing so, solitons (= “self-guiding light bullets”) are created which cover together a very large spectral range, called supercontinuum. Often, the supercontinuum ranges from 530-1100nm but depending on the fiber material, design, length and input laser parameter, different spectral ranges can be covered. Right now, to my knowledge the record covers a wavelength range from 1-5µm using an 8mm telluride PCF.
During the last years supercontinuum spectrums have found applications in spectroscopy. But the most famous, and perhaps most important one, application is on the field of laser based precision spectroscopy, for precision measurements of atomic structures and optical frequencies. Thereby the optical frequency comb technique is applied, which is based too on fiber generated supercontinuum. In 2005, Theodor Hänsch (Max Planck Institute of Quantum Optics) was one of the Nobel Prize winners “for their development of laser based precision spectroscopy, that is, the determination of the colour of the light of atoms and molecules with extreme precision.” Without fiber generated supercontinuum, hence without photonic crystal fibers, these very accurate measurements wouldn’t have been possible. And public life is also profiting from these experiments, because e.g. it helps to improve GPS systems.
Today, many different kind of photonic crystal fibers exist with different properties (see picture). Some have instead of a core a whole, so called hollow core fiber, other ones are doped in the core or cladding with another material, mostly Ytterbium (Yb) or Erbium (Eb). These doped fibers are extensively used in fiber amplifiers and fiber lasers, probably the next generation of lasers.
Photonic crystal fibers are at the very beginning to enter scientific experiments in a broad application range, and because of their special properties we can expect many new techniques and exciting discoveries. Hence, it is a good time to consider PCFs in your experiment…and perhaps you may be awarded with the Nobel Prize some years later ;).

Review Articles:
Photonic Crystal-Fibers
by P. St. J. Russell
JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 24, NO. 12, DECEMBER 2006

Nonlinear Waveguides Optics and Photonic Crystal Fibers
by J. C. Knight
Optics Express Vol. 15, pp 15365

Research Groups:
Russell Group at Max Planck Institute for the Science of Light, Erlangen

Centre for Photonics & Photonics Material, University of Bath

Optoelectronics Research Centre, University of Southampton

Companies:
NKT Photonics
(former called Crystal-Fibre)
with the well-known distributors
Thorlabs and Newport

Nufern

nLIGHT
(former Liekki, acquired by nLIGHT)

Laser and armies.

While the laser is always presented as a big destructive weapon in any science fiction story, the reality is that they haven't play a role at all as weapons. They are extensively used as guidance systems, detection systems and such, but not direclty as weapons, until now.

Here is an entry from the Boing Boing blog about Boeing getting money from the US army to build big lasr that they promes can harm the enemy's army.

" The Advanced Tactical Laser (ATL) is a directed energy weapon (aka ray gun) developed by Boeing under a US military contract. According to an overview document (PDF) about Boeing's Directed Energy Systems program, "In August 2009, the ATL defeated a ground vehicle target from the air, demonstrating its first air-to-ground, high-power laser engagement of a tactically representative target." The video above documents that experiment, in which the laser weapon, mounted on a C-130H Hercules transport plane, was fired at a car. See the Boeing site for more videos, including aerial footage. (via Smithsonian Air & Space) "

More details here. And some videos here.

Nobel Prize 2009: Kao, Boyle and Smith

Nobel Prize 2009 for Charles K. Kao "for groundbreaking achievements concerning the transmission of light in fibers for optical communication" and W. S. Boyle and G. E. Smith "for the invention of an imaging semiconductor circuit – the CCD sensor".

Charles K. Kao was born 1933 in Shanghai, China. He got his Ph.D. in Electrical Engineering 1965 from Imperial College London, UK. He worked at Standard Telecommunication and Chinese University of Hong Kong. He retired in 1996.
Willard Sterling Boyle, was born 1924 in Amherst, NS, Canada. He got his Ph.D. in Physics 1950 from McGill University, QC, Canada. He was the executive Director of Communication Sciences Division, Bell Laboratories, Murray Hill, NJ, USA; he is retired since 1979.
George Elwood Smith, was born 1930 in White Plains, NY, USA. He got his Ph.D. in Physics 1959 from University of Chicago, IL, USA and also worked Bell Laboratories He got retired in 1986.

Why is their contribution so important? C. Kao has been awarded the Nobel Prize due to his prediction of the optical fiber. Thanks to his discovery, you are reading this! Optical fibers are widely used in communications; it allows information spreading almost at the speed of light.
Boyle and Smith invented the CCD (charged coupled device). Do you have a digital camera? If the answer is yes, thank Boyle and Smith! CCD sensors are sometimes called "the electronic eye". Without them, not only the digital camera would have taken a slower course, but also the images from telescopes or the way we analyze beams in optics.

To know more about their contribution to Physics (and particulary to Optics), I recommend you to download the digest with easy-reading information for the public about their work.

You can find more information about Nobel Laureates at http://nobelprize.org (you can even ask them a question!); a more detailed report (but still easy to understand) can be found here.

Breaking the Optical Resolution Limit by Near-field Microscopy

Gaining spectroscopic information of a sample by optical image devices (spectrometers, fourier transform spectroscopy) is a daily and important task in science. But it encounters a fundamental problem when used in nanotechnology where sample structures can have dimensions of a few nanometers. Then the optical resolution is limited by diffraction to about half the used wavelength. For the visible spectrum this means a possible resolution of around 300nm but for the infrared (1-50µm) or terahertz (50 - 500µm) regime this allows only µm resolution, far too bad for nanotechnology. Different techniques like AFM, SEM or TEM exist to examine nanoscaled samples but all of them lack to gain directly spectroscopic information. This gap can be closed by near-field microscopy.
The most advanced near-field technique, called s-SNOM for scattering scanning near-field optical microscope, is based onto an AFM in tapping mode. Additionally to an ordinary AFM, a laser is focused onto the cantilever tip apex generating a nano-focus locally illuminating the sample surface. The interaction between the nano-focus and the sample scatters the light which will be modified in amplitude and/ or phase. Scanning the sample and recording for every pixel the scattered light allows obtaining an optical image. Thereby the optical resolution is only determined by the tip apex radius and independent of the illuminating wavelength! This has been demonstrated from the visible to the THz [1]. Routinely, 20nm is achieved but sub 10nm has been demonstrated too. For gaining spectral information the wavelength has to be changed and a new picture to be taken. Comparing the different pictures enables to gain the desired spectral information of the material properties, like the chemical composition, crystal structure or mobile carrier density which is very interesting for the semiconductor industry [2,3]. But also applications in biology are possible as demonstrated with a tobacco virus [4]. Thereby s-SNOM benefits from the advantage that its sample hasn’t to be labeled as it often necessary in biology. Currently, different approaches are underway to replace the tunable laser source by a broadband source to record the spectral information in one measurement attempt. Today, s-SNOM starts to enter several labs of research groups completing their analysis tools for nanotechnology. Hence, keep your eyes open, especially on the nanoscale!

University Groups:
Nanogune, San Sebastian
University of Washington
University of Rochester
ICFO, Barcelona

Company:
Neaspec GmbH

References:
[1] Terahertz Near-Field Nanoscopy of Mobile Carriers in Single Semiconductor Nanodevices, A.J. Huber, Nano Lett., 2008, 8 (11), pp 3766–3770

[2] Simultaneous IR Material Recognition and Conductivity Mapping by Nanoscale Near-Field Microscopy, A.J. Huber, Volume 19 Issue 17, Pages 2209 - 2212

[3] Controlling the near-field oscillations of loaded plasmonic nanoantennas, M. Schnell, Nature Photonics 3, 287 - 291 (2009)

[4] Infrared Spectroscopic Mapping of Single Nanoparticles and Viruses at Nanoscale Resolution, M.Brehm, Nano Lett., 2006, 6 (7), pp 1307–1310

World's fastest camera

The technique, called Serial Time-Encoded Amplified imaging (STEAM), is based on supercontinuum laser pulses (ie., ultrabroad bandwidth pulses). The pulses are propagated to a bidimensional colour matrix by two optical elements. Then, the beam lights the samples: a part of it is reflected by the sample, depending on the dark and light areas of the illuminated point, and the reflections come back through the same way. Since the propagation of the different colours of the pulse is so regular, the range of reflected colours have detailed spatial information about the sample.

According to Bahram Jalali, professor of the University of California and director of this research, "the light points reflects their assigned wavelength, but the dark ones do not, so when the bidimensional rainbow is reflected in the object, the image is copied over the pulse spectrum". The pulse goes back through the optical dispersive system and is converted once more in a single spot, with the image saved in a serie of distributed colours; then, the beam goes through a dispersive fiber (ie., an optical fiber with different velocity limits for each colour). As result, the red part of the spectrum travels at different from the blue, they get separated and finally they arrived at different moments. The signal is then detected by a photodiode and the image is reconstructed. As a result of this technique, an improvement of the speed of images recording is improved (it is the same as the laser repetition rate) with a very high spatial resolution. This could find a wide variety of applications, such as pictures of blood or even the internal structure of the cells.

Teleportation –from Fiction to Reality?

“Beam me up, Scotty”, who hasn’t yet heard this phrase from Star-Trek? Beaming – alias teleportation –is a favored part of many science fiction stories and thus well-known by publics. Probably most of us would like to have a teleportation tool, for saving stressful traveling time, or to experience famous adventures on alien planets… During the last ten years you may have heard that scientists have successfully entered the field of teleportation. But, is it the same teleportation as in Stark Trek? Let us find out what fiction is and what to reality belongs.

In Star Trek, humans and materials are teleported with superluminal speed from one place to another – empty - place. Thereby, teleported is the matter (atoms) or energy and the information in which state the matter is. Mostly, the teleportation process is controlled by a station which can act as receiver or sender. In Science things are a bit more complicated as usual, but the good news is that there exists no physical law which prohibits the teleportation of humans – it is only quite complex to do so. Today, mostly single photons are teleported. Contrary to Star Trek and similar, in reality you can teleport only the information of a state and not its matter or energy. As a consequence, you need at the receiver place already the same type of matter/ energy onto which you can overwrite the state of the particle which you want to teleport. Furthermore, you can´t do it with superluminal velocity, hence no causality violation. The reason is that the particle at the sender and the one at the receiver´s place have to be specially prepared, namely to be entangled together. The entanglement allows the teleportation of the state of a particle with superluminal velocity (Einstein called it “spooky action at a distance”) but to read out this information for further processing, the receiver needs some special information from the sender -after he performed a special action to the particle- which he can get only with not superluminal velocity (by phone etc). Another point is the entanglement process for more complex systems. Photons and ions are routinely entangled, but even simple molecules are very hard to do so. To my knowledge, single Buckminsterfullerene (C60, 60 carbon atoms) are the biggest systems which have been entangled (diameter around 0.7nm). But they haven’t yet been teleported, because as larger an entangled system is, as shorter the duration of the entanglement state. Now, imagine a human body and you will understand why it is quite difficult to teleport us. Hence, “beam me up, Scotty” has to stay for longer time in fiction.

These days, teleportation in the lab with photons is already routinely done. The teleported distance increases continuous and is over 100km for teleportation in free space as in fibers. Furthermore, teleportation using ions (spin) have been demonstrated too. In future, scientists are planning to teleport larger atom complexes (fullerene) up to small bacteria. But until this time has arrived, new techniques have to be developed.

Nevertheless, theoretically humans could be teleported but the question arises, if our body is teleported, will our spirit, our soul be teleported too? Nobody knows.

Video from the teleportation group in Geneva (in french):

Links to teleportation groups:
Geneva, Prof. Gisin
Munich, Prof. Weinfurter
Vienna, Prof. Zeilinger

Pink is not a colour

Have a look at the visible spectrum; you can see many colours: red, blue, green, yellow... but what about pink?

You can not find it in the spectrum... but then, why do we see it? Basically, we could say that the reason is just the difference between wavelength (property of waves) and colour (asigned by the brain).

When the eye perceives just one wavelength (for example 600 nm), our brain identifies the colour of that wavelength (in this example, red).

But, what happens if the eye receives light of more than one wavelength? In this case, the colour interpreted by the brain is usually the sum of the input responses on the retina, i.e. the colour halfway between them... except when the wavelengths come from both ends of the light spectrum at once (i.e. red and violet light).

In this case, the colour halfway would be green (not very representative of the mixture), so the brain simply invents a new colour halfway between them: pink (or magenta, according to its official name).

This post has been adapted from http://www.biotele.com/magenta.html. You can find there a extended version.

Ultra-Fast Dynamics Imaging

Hi, my name is Camilo Ruiz and i am special correspondent sent to the island of Ischia close to Naples Italy for the conference Ultra-Fast Dynamics Imaging celebrated from 30/04 - 03/05 in 2009.

This small workshop was organized by the local group at University of Naples and many of the most important players in the attosecond science were invited to participate. While attosecond is all about precious stability only achieved in well equipped and rich labs, everybody was happy to be invited to the southest part of Europe, where the sun is always there and there is not much of a rush, so we had a perfect combination.



The full program of the conference as well as the book of abstract can be found in the conference web page , i will instead point out some of the topics that i liked more together with some references.

On wednesday 29th, we had several good results. From the University of Frankfurt, Reinhard Dörner presented a paper on "Inteference and electron entanglement in photoionization of H2 and N2", this work is published in Science recently and explore the question of electron localization: When a diatomic molecule absorb a big photon a hole is produce because a k-shell electron is ionized, but then the question is weather the hole created is localized or not. In the case of the hole being localized, the electron hole should hope in 20 fs, later in time an Auger electron should be emitted to fill the hole. If this electron is emitted from one electron only, it should be diffracted but if it is not localized, probably the diffraction will be vanished.

Quotimg the reference: "Whether the core hole is better thought of as being localized or delocalized depends on the direction in which the photoelectron or Auger electron is emitted. Detecting the direction of the photoelectron in the experiment selects between cases in which the transient core hole is best described by a delocalized state of g or u symmetry, and other cases for which it is more appropriate to think of a localized hole. This situation can be described by a coherent superposition of gerade and ungerade states, or alternatively by a superposition of states corresponding to a hole on the left and one on the right."

Certainly there is more to it, as the enviroment breaks this description, but as expected the answer is very quantum like. These are beautiful experiments which don't even need a fast pulse, these are synchrton radiation only. Will time might play a role? Lets find a 419 eV photons in a short pulse to answer that.

The gropu of Garching talked about the new set of experiments in solid interfaces, these are very interesting results, more interesting is the new rout of this leading lab which will concentrate on multiple streaking. As this is something i am also doing i will not mention anything more about it. But try this paper.

These are just two talks, so you can imagine the number of things happening. The next message might be about the new XFELs around the globe.

First light from world's first hard X-ray laser

A couple of days ago, it was published that the the world's first X-ray laser (LCLS) has achieved "first light".

When fine tuning is complete, the LCLS will provide the world's brightest, shortest pulses of laser X-rays for scientific study. As tool for studying the arrangement of atoms in materials, this source will find a wide range of applications in science.

(I love this video, you can really feel the passion of these scientists for their work)

But do you know how it works?

Imagine an accelerated electron bunch which goes through a sinusoidal transverse magnetic field. It will experience a force given by F=q(E+vxB) (Lorentz's force) and thus the trajectory will be sinusoidal too; if the trajectory is a curve, the electrons suffer centripetal acceleration. As it is well known, a charged accelerated particle emits radiation (Lienard-Wiechert). In the Spring-8 website, you can download a program to simulate the radiation emitted by an electron in different magnetic fields.

Due to the electron-radiation interaction, the electrons form electron bunches which emit coherently and the intensity is increased.

These systems are called free electron lasers (FEL); they consist on an accelerator (formed by klystrons which deliver microwave radiation to accelerate the electron and a resonator) and a ondulator (a periodic structure of magnets to produce the sinusoidal transverse magnetic field).

The main problem of these facilities is the size and cost.
Another approach to get X-rays is based on high power lasers: instead of the accelerator, a high-power laser accelerates the electrons which go later through the ondulator. This implementation leads to a reduction of energy and size (in fact, these systems are called Table-Top XFEL).

Prof. Sánchez Ramos awarded Best Invention of the Year

Spanish researcher Professor Celia Sánchez Ramos, has been awarded in Geneva with a prize for the Best Invention of the Year given by the World Intellectual Property Organisation.
Prof. Sánchez Ramos, who is a researcher at the Complutense University in Madrid (UCM), invented a light filter for contact lenses to protect the retina and prevent blindness.
Between 15% and 20% of the light spectrum consists of harmful colours for us (blue and violet), which destroy the retina neurons leading to a degeneration into the macula (DMAE); the fovea, a part of the retina structure, protects us from these colours. Prof. Sánchez Ramos proved that this part of the spectrum could be blocked by inserting a yellow filter into the lenses.
In spite of being yellow, the lens does not vary the perception of the person.
To test the efficiency of the lens, the researcher carried out a experiment with rats exposed to different light types and rabbits which had been previously operated for cataracs.
Nowadays, the UCM is carrying out a clinic trial in 23 hospitals with people operated for cataracs.

Michelson interferometer

Maybe you have ever heard that "light+light=darkness". Today, we will try to explain this and build a home-made Michelson interferometer to prove it.

Interferences

In physics, we define an interference as the superposition of two or more waves. Depending on the kind of wave, the pattern is different: for example, the interference of two spherical waves is a pattern of rings, while the pattern for plane waves are fringes.

But, why don't we see this phenomenon if we switch on two lamps?

Well, it has to do with the "coherence": for a simple explanation, we could translate this in waves coming from the same source or having nearly the same frequency. It is also possible to get them with non-monochromatic waves, but in these case they have to have the same range of wavelengths and same phase differences for each wavelenght (for instance, you can see interferences from sunlight when there is oil on a road).

Michelson interferometer

In the picture below, you can see what is called Michelson interferomter.

Let's explain how it works: coherent light emitted from a source (for example, a laser or a sodium lamp) travels up to a beamsplitter (BS), a device capable of dividing a beam into two beams (it is basically a glass with one of its surfaces partially reflective). From there, one of the beams goes to a first mirror (M1) where it is reflected; the same happens to the second beam. In the beamsplitter they meet again and travel together to the observation screen. Notice that there is an adittional glass (the blue one in the figure) to compensate the paths (the first beam goes twice through the beamsplitter and the second one just once).

In the following film from the Celtic Mad Scientist you can learn how to build your own Michelson interferometer, as well as applications and a detailed description of the setup:

For students of advanced levels, you should notice that if the interferometer was perfectly align you would get the interference of two plane waves with the same propagation vector (as they should be pararell) and thus there should not be interference fringes! Obviously, it is not the case here: since it is not perfectly aligned, there is a slighty angle between the two beams that allows you to see the fringes.

As curiosity you should know that, together with Edward Morley, Abraham Michelson tried to demonstrate with this system the existence of the "ether" in 1887. In the 19th century, it was believed that the Earth was surronded by a gas called ether. Michelson and Morley wanted to measure the speed of the Earth with respect to the ether. This movement will produce a wind and, since the light propagated through the ether, the speed of light would be different depending on the propagation direction. In one of the interferometer arms, the light would propagate in the same direction as the wind, but in the other one would propagate against the wind and thus more slowly.

However, they did not find any differences; the "failure" of the experiment showed the non-existance of ether and the propagation of light in vacuum.

In this link, you can find an interactive movie where you can reproduce the experiment and in the AIP Center for History of Physics you can download the original article.

How to measure the speed of light with a liquorice stick

Try the following experiment at home (all you need is a liquorice stick and a microwave oven):

Can you guess why the value you have calculated is the speed of light?
First of all, let's explain how the microwave oven works.

The oven acts as a cavity for the waves; thus, the waves are no longer travelling waves, but standing waves.

As you can see in the video, the amplitude remains zero at some points which are separated half wavelenght. For this reason, the stick is not burnt at these points.

Since the speed of light is the product of the frequency (given by the oven specifications) by the wavelength, which can be deduced from the distance between two non-burnt points, it is easy to get a good approximation for it.

This experiment has been adapted from "Cuaderno de bitácora estalar"

Funny webs for funny science

Surfing into the net today, I have found two very amusing web sites that I strongly recommend you to visit.

• The first one, "The Naked Scientists", is, in their own words, "group of physicians and researchers from Cambridge University who use radio, live lectures, and the Internet to strip science down to its bare essentials, and promote it to the general public". Simply wonderful.
• The second one is "Cuaderno de bitácora estelar", by D. Barrado and B. Montesinos; it is a blog where interesting topics related with science and astrophysics fare presented so that everybody can understand them.

Enjoy them!

Laser cooling

If you want to know what laser cooling is, Nobel Laureate Steven Chu delivers a Lecture at UC Berkeley under the title "Laser cooling: from atomic clocks to watching biomolecules" that you can watch here:

The dancer

In which way is the woman dancing? Clockwise or anti-clockwise? Sure?
It spins in the way you want to!
Don't you trust us?
Think about the fact that the image is not a tridimensional (since it is on your PC screen, it can just have two dimensions), so it can not have a rotational movement. If you want to see it spinning on the other way, have a look for one moment to the other side of the screen.
But why do you see in one or the other way?
The image has been extracted from an austrilian newspaper:
http://www.news.com.au/heraldsun/story/0,21985,22556281-661,00.html
As it is explained here, it could depend on which side of your brain you use more.

Transverse modes

Have a look at this video:


What you are watching here are acoustic harmonics (pay attention to the way they change depending on the sound frequency). The acoustic waves produce vibrations on the table which are proportional to the the intensity pattern.

In a very simple model, a laser can be described as a cavity with an active medium inside. The field pattern measured in a perpendicular plane to the cavity is the so called transverse mode. They depend on the cavity geometry.

Some examples:



They are denoted by TEMplq, where p is the number of radial zero fields, l is the number of angular zero fields and q is the number of longitudinal fields. The TEMoo is usually preferred as it is easier to be focused.