A new Bose-Einstein condensate

Originally published here.

A new Bose-Einstein condensate

 

Although Bose-Einstein condensation has been observed in several systems, the limits of the phenomenon need to be pushed further: to faster timescales, higher temperatures, and smaller sizes. The easier creating these condensates gets, the more exciting routes open for new technological applications. New light sources, for example, could be extremely small in size and allow fast information processing.

In experiments by Aalto researchers, the condensed particles were mixtures of light and electrons in motion in gold nanorods arranged into a periodic array. Unlike most previous Bose-Einstein condensates created experimentally, the new condensate does not need to be cooled down to temperatures near absolute zero. Because the particles are mostly light, the condensation could be induced in room temperature.

‘The gold nanoparticle array is easy to create with modern nanofabrication methods. Near the nanorods, light can be focused into tiny volumes, even below the wavelength of light in vacuum. These features offer interesting prospects for fundamental studies and applications of the new condensate,’ says Academy Professor Päivi Törmä.

The main hurdle in acquiring proof of the new kind of condensate is that it comes into being extremely quickly.’According to our theoretical calculations, the condensate forms in only a picosecond,’ says doctoral student Antti Moilanen. ‘How could we ever verify the existence of something that only lasts one trillionth of a second?’

Turning distance into time

A key idea was to initiate the condensation process with a kick so that the particles forming the condensate would start to move.

‘As the condensate takes form, it will emit light throughout the gold nanorod array. By observing the light, we can monitor how the condensation proceeds in time. This is how we can turn distance into time,’ explains staff scientist Tommi Hakala.

The light that the condensate emits is similar to laser light. ‘We can alter the distance between each nanorod to control whether Bose-Einstein condensation or the formation of ordinary laser light occurs. The two are closely related phenomena, and being able to distinguish between them is crucial for fundamental research. They also promise different kinds of technological applications,’ explains Professor Törmä.

Both lasing and Bose-Einstein condensation provide bright beams, but the coherences of the light they offer have different properties. These, in turn, affect the ways the light can be tuned to meet the requirements of a specific application. The new condensate can produce light pulses that are extremely short and may offer faster speeds for information processing and imaging applications. Academy Professor Törmä has already obtained a Proof of Concept grant from the European Research Council to explore such prospects.

Materials provided by Aalto University. Note: Content may be edited for style and length.

Journal Reference:

1 Tommi K. Hakala, Antti J. Moilanen, Aaro I. Väkeväinen, Rui Guo, Jani-Petri Martikainen, Konstantinos S. Daskalakis, Heikki T. Rekola, Aleksi Julku, Päivi Törmä. Bose–Einstein condensation in a plasmonic lattice. Nature Physics, 2018; DOI: 10.1038/s41567-018-0109-9

Physicists are planning to build lasers so powerful they could rip apart empty space

Physicists are planning to build lasers so powerful they could rip apart empty space | Science | AAAS
Physicists are planning to build lasers so powerful they could rip apart empty space

By Edwin Cartlidge

big_laser_0123.jpg?itok=SbIUYA-w

A laser in Shanghai, China, has set power records yet fits on tabletops.

KAN ZHAN

Inside a cramped laboratory in Shanghai, China, physicist Ruxin Li and colleagues are breaking records with the most powerful pulses of light the world has ever seen. At the heart of their laser, called the Shanghai Superintense Ultrafast Laser Facility (SULF), is a single cylinder of titanium-doped sapphire about the width of a Frisbee. After kindling light in the crystal and shunting it through a system of lenses and mirrors, the SULF distills it into pulses of mind-boggling power. In 2016, it achieved an unprecedented 5.3 million billion watts, or petawatts (PW). The lights in Shanghai do not dim each time the laser fires, however. Although the pulses are extraordinarily powerful, they are also infinitesimally brief, lasting less than a trillionth of a second. The researchers are now upgrading their laser and hope to beat their own record by the end of this year with a 10-PW shot, which would pack more than 1000 times the power of all the world’s electrical grids combined.

The group’s ambitions don’t end there. This year, Li and colleagues intend to start building a 100-PW laser known as the Station of Extreme Light (SEL). By 2023, it could be flinging pulses into a chamber 20 meters underground, subjecting targets to extremes of temperature and pressure not normally found on Earth, a boon to astrophysicists and materials scientists alike. The laser could also power demonstrations of a new way to accelerate particles for use in medicine and high-energy physics. But most alluring, Li says, would be showing that light could tear electrons and their antimatter counterparts, positrons, from empty space—a phenomenon known as “breaking the vacuum.” It would be a striking illustration that matter and energy are interchangeable, as Albert Einstein’s famous E=mc2 equation states. Although nuclear weapons attest to the conversion of matter into immense amounts of heat and light, doing the reverse is not so easy. But Li says the SEL is up to the task. “That would be very exciting,” he says. “It would mean you could generate something from nothing.”

The Chinese group is “definitely leading the way” to 100 PW, says Philip Bucksbaum, an atomic physicist at Stanford University in Palo Alto, California. But there is plenty of competition. In the next few years, 10-PW devices should switch on in Romania and the Czech Republic as part of Europe’s Extreme Light Infrastructure, although the project recently put off its goal of building a 100-PW-scale device. Physicists in Russia have drawn up a design for a 180-PW laser known as the Exawatt Center for Extreme Light Studies (XCELS), while Japanese researchers have put forward proposals for a 30-PW device.

Largely missing from the fray are U.S. scientists, who have fallen behind in the race to high powers, according to a study published last month by a National Academies of Sciences, Engineering, and Medicine group that was chaired by Bucksbaum. The study calls on the Department of Energy to plan for at least one high-power laser facility, and that gives hope to researchers at the University of Rochester in New York, who are developing plans for a 75-PW laser, the Optical Parametric Amplifier Line (OPAL). It would take advantage of beamlines at OMEGA-EP, one of the country’s most powerful lasers. “The [Academies] report is encouraging,” says Jonathan Zuegel, who heads the OPAL.

Invented in 1960, lasers use an external “pump,” such as a flash lamp, to excite electrons within the atoms of a lasing material—usually a gas, crystal, or semiconductor. When one of these excited electrons falls back to its original state it emits a photon, which in turn stimulates another electron to emit a photon, and so on. Unlike the spreading beams of a flashlight, the photons in a laser emerge in a tightly packed stream at specific wavelengths.

Because power equals energy divided by time, there are basically two ways to maximize it: Either boost the energy of your laser, or shorten the duration of its pulses. In the 1970s, researchers at Lawrence Livermore National Laboratory (LLNL) in California focused on the former, boosting laser energy by routing beams through additional lasing crystals made of glass doped with neodymium. Beams above a certain intensity, however, can damage the amplifiers. To avoid this, LLNL had to make the amplifiers ever larger, many tens of centimeters in diameter. But in 1983, Gerard Mourou, now at the École Polytechnique near Paris, and his colleagues made a breakthrough. He realized that a short laser pulse could be stretched in time—thereby making it less intense—by a diffraction grating that spreads the pulse into its component colors. After being safely amplified to higher energies, the light could be recompressed with a second grating. The end result: a more powerful pulse and an intact amplifier.

2015 – International Year of Light

2015 has been declared the International Year of Light (IYL 2015) and with me being an optics geek, well, it was difficult to resist to enter a post about it. The IYL 2015 is a global initiative adopted by the United Nations to raise awareness of how optical technologies promote sustainable development and provide solutions to worldwide challenges in areas such as energy, education, communications, health, and sustainability.

There will be a number of event and programs run throughout the year and the aim of many of them is to promote public and political understanding of the central role of light in the modern world while also celebrating noteworthy anniversaries in 2015 – from the first studies of optics 1000 years ago to discoveries in optical communications that power the Internet today.

You can find further information from the well-known OSA here and check out the International Year of Light Blog.

Here are some pictures I took a couple of years ago during CLEO Europe in relationship to the International Year of Light.

Quantum Tunnel Answers: Fresnel Lens

Hello everyone,

once again we have a question coming to the inbox of the Quantum Tunnel blog. If you are interested in asking a question, please feel free to get in touch using this page. We have once again a question by a very avid reader, let’s take a look:

Dear Quantum Tunnel,

Could you please explain how Fresnel lenses work? I am asking after listening to Dr Carlos Macías-Romero talking in one of the Quantum Tunnel podcasts. Thanks a lot.

Pablo

Hello yet again Pablo, thanks a lot for your question. Well, I assume that you are familiar with the idea of a lens and that you may even wear a pair of spectacles or know someone who does and so you know that you can correct, among other things, the focal point and thus read your favourite blog (the Quantum Tunnel site of course!) with trouble.

Well, have you ever had a chance to go and see a lighthouse close enough? But not just the building, the actual place where the light is beamed out to see? If so you may have seen the lenses they use. If not, take a look the image here:

Lighthouse Lens
Lighthouse Lens (Photo credit: Wikipedia)

You can see how the lens is made out of various concentric layers of material and the design allows us to construct lenses that otherwise would be way to thick and therefore heavier. A lighthouse requires a light beam that uses a large aperture but a short focal length and a Fresnel lens offers exactly that without the need of a really thick lens. Fresnel lenses are named after the French physicist Augustin-Jean Fresnel.

Another example of Fresnel lenses are flat magnifying glasses such as the one shown below, you can see that they are effectively flat and no need to use one such as those used by Sherlock Holmes…

English: Creditcard-size Fresnel magnifier Ned...
English: Creditcard-size Fresnel magnifier Nederlands: Fresnelloep in creditcardformaat (Photo credit: Wikipedia)

The design of a Fresnel lens allows it to capture more oblique light from a light source. Remember that a lens works by refracting (bending) the light and the way in which the “layering” in the Fresnel lens helps with the refraction needed. See the diagram below:

Fresnel lens

A couple of other uses for these lenses are in overhead projectors and the headlights of cars. So next time you attend or give a lecture or drive at night, think of Monsieur Fresnel.

Hawthorne Effect

School meals
School meals (Photo credit: Coventry City Council)

I was listening last week to the “More or Less” podcast with Tim Harford, which by the way is one of my favourite Radio 4 programmes and I highly recommend it. In the programme they were discussing the proposal of Mr Nick Clegg, the UK’s Deputy Prime Minister, to offer free school lunches to all pupils at infant schools. The proposal follows from a pilot study  that seemed to suggest that giving free meals to school children was good for their academic performance.

As usual, not all is what it seems and the programme goes on to discuss this. I’m afraid is the old adage of correlation and causation… In any case, the commentators in the programme made a reference to the Hawthorne effect, and although Tim Harford mentioned something about this I ended up with the curiosity to find out more about it. It turns out that the Hawthorne effect is at work when subjects modify and change their behaviour in response to the fact that they know they are being studied. You might think that this is similar to the quantum mechanical observer affecting the system they observe, except that in this case the system is patently aware of the influence of the observation. I would leave it at that…

The effect is named after Western Electric’s  Hawthorne Works in Cicero, Il somewhere close to Chicago. Between 1924 and 1932 Elton Mayo carried out some productivity trials that have become some of the most well-know in social science, as the study is often held as a demonstration that people respond to change when they know you they are being observed or studied. So, who knows, perhaps the pupils, parents and teachers did indeed change their behaviour while the study was taking place… Oh well…

Babinet-Soleil Compensator

The Babinet-Soleil Compensator is a variable waveplate which, for example, can convert circularly polarised light into linearly polarised light or vice versa. It comprises two opposed birefringent crystal wedges with a compensating crystal block in optical contact with the smaller wedge. Both wedges are cut with the optic axis parallel to their long edges, and the compensating block has its axis at right angles. In operation, the large wedge is translated across the smaller, thus presenting a variable path length difference to an optical beam passing through the instrument. The compensating block ensures that this difference is uniform across the aperture.