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

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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.

Laser – Sci-advent – Day 15

Laser Experiment Blue

Lasers have become so common that the number of applications they have do not surprise us. Nonetheless, their characteristics still captivate all of us. Laser is an acronym of Light Amplification by the Stimulated Emission of Radiation and it is indeed a very descriptive name.

A laser consists of three main elements: a gain medium, an energy source and a device to provide feedback to the system. The amplification of the electromagnetic radiation is done by gain medium. This is possible by pumping energy to the system and thus generating stimulated emission. It is very common for typical lasers to use feedback from an optical cavity, such as a pair of mirrors at each end of the gain medium.

Laser light is characterised by properties such as monochromaticity, coherence and power.

 

Quantum Tunnel Podcast – What makes laser light so special?

You can download and listen to this episode here.

What makes laser light so special?
When we look at a light source, we can immediately tell whether the source is a laser or not, but what are the main properties that a laser has that distinguish it from any other “normal” source of light.

Oscar Price and Adam Bekele have spent a week at the Photonics Group at Imperial College London working on some theoretical aspects to describe laser behaviour. In this episode, Adam and Oscar will tell us something about properties such as monochromaticity, directionality and coherence, that make of the laser a very special form of light.

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I’m not a scientist, but I had a go… Students during work experience

During the last five days Adam Bekele and Oscar Price were visiting the Photonics Group at Imperial College, where they had a go a understanding some laser theory. Here is what they have to say about this week… Ah, and please check out the Quantum Tunnel Podcast, where Oscar and Adam will tell us more about lasers! (I will let you all know when the podcast is actually available)

Adam Bekele

After a week’s work at Imperial College I have gained a lot of understanding about the works of researching physicists and high level PhD students. Dr Jesús Rogel- Salazar has introduced us to both theoretical and experimental physicists. The students showed us what they were currently researching and what their day to day work entails. It has been immensely inspiring.

We have especially been working on explaining certain behaviours of LASERs. Amongst many other things, we used methods of differential equation to solve the rate of emitted photons through stimulated emission, therefore showing how lasers are created. It has been really useful as it has really accentuated my perception of how interrelated mathematics and physics are. The week has certainly lived up to my expectations and beyond, and I thank Imperial College and especially Dr Jesus Rogel-Salazar.

oscar2Oscar Price
As expected, my week at imperial has taught me a lot; what was not so expected was the relaxed nature of the students and staff I was working with. The apprehension I had of Imperial College could not have been further from the truth, nowhere could I find the strict controlling lecturers I had so frequently depicted.

Aside from the College itself, I was also surprised by the high levels of physics I encountered, the surprising aspect being the uncertainty of it all. I used to think of physics as being one of the most black and white subjects there was, how wrong I was. My discovery of this uncertainty has only deepened my interest in the subject and added to the countless questions already in my head. I thank Imperial College and Dr Jesús Rogel-Salazar for these questions and I hope to show my appreciation by answering them in the years to come.

I’m not a scientist, but let me have a go… Students during work experience

This week I have the pleasure to have a couple of enthusiastic students doing a bit of work experience with me at Imperial College working on lasers and their applications. Keep an eye here as they might also feature in the Quantum Tunnel Podcast!

adambekele
My name is Adam Bekele, a sixth form student at Camden School for Girls. I am doing my A levels and I have just finished my first year AS in Maths, Further Maths, Physics and History. I have always loved Maths and Physics. Maths is very intriguing as it exercises your problem solving skills, especially at A level and above, as we start looking at more complex mathematical ideas. Physics complements mathematics, it shows you the real life uses of mathematical ideas and that is what I find most interesting.

I am doing work experience with Dr. Jesus Rogel-Salazar at Imperial College London. I am really looking forward to this week as we will be working with Lasers, the uses, mechanism and the science behind it all. From this week, I would like to gain an understanding of how Laser behaviour can be explained mathematically, using graphs etc. It would also be interesting to find out about the types of mathematical equations that theoretical physicists have to solve in order to explain things such as Lasers. In doing this I would be able to also look at the use of computer programs within mathematics and physics. At school we have been studying energy levels and the nature of light so this work experience would better my understanding of this topic as they are very much related. It would also enable me to get a grasp of the type of things I would be doing as physics undergraduate and go beyond the school curriculum.

I have many hobbies. I play three instruments, saxophone, clarinet and bass guitar. I very much enjoy practising my instruments and playing in a band. I also row in a club, Royal Docks Rowing Club. Besides these things I also like running and doing art in my spare time.

oscarprice

My name is Oscar Price and I am a sixth form student at Camden School for Girls. The processes of GCSEs are what really sparked my interest for physics. I found that at GCSE many of the lessons endured are taught by teachers only aiming to guide you through the course you have chosen and not teach you the subject itself. They lacked passion. The result of this for me was boredom which gradually turned into a dislike of the subject, however this was not the case with physics. However tedious a certain topic would be made to seem, the fact that the principles I was learning were applicable to almost every aspect of daily life gripped me. I could find no other subject that could relate to or explain the World in quite the same way, I was inspired and remain to be so.

For the purpose of “broadening my horizons”, as my parents would say, and padding out my University application form, I took up the offer of a week’s work placement at the Physics Department in Imperial College London with Dr Jesus Rogel-Salazar working on the theory and applications of lasers. From it I hope to develop my understanding and interest of the subject while confirming it to be the right choice for me at university.