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.