The problem
RECENT IMPROVEMENTS IN technology have allowed scientists to accelerate electrons in ways that create high-energy, extremely bright, and short laser pulses. Before the invention of these lasers, scientists could not study how high-intensity ultraviolet and X-ray light interacts with matter. Now that such lasers exist, everybody’s dying to know what happens when you blast stuff with short, high-intensity, high-energy laser beams.
The obvious answer is that you blow shit up, and that’s cool and all, but the potential applications of these beams are much greater than that. High-intensity ultraviolet and X-ray lasers might be able to image materials that are currently challenging to study. But before scientists can use these lasers, they have to understand this completely unexplored area of light-matter interaction.
The researcher
Lora Ramunno studies computational photonics at the University of Ottawa. Using her parallel supercomputer (equivalent to about 600 desktops), Ramunno studies nonlinear optical imaging and the interaction between matter and intense laser beams.
The project
Ramunno decided to look at how tiny clusters of matter interact with a high-intensity laser pulse by simulating each and every one of the atoms. When atoms are hit by a photon of light there is some probability that they will absorb the photon and eject one of their electrons. This leaves the atom as a positively charged ion. At every step of her simulation, Ramunno’s computer program must stop and evaluate the quantum probabilities that give these rates before it can move on to the next step.
The key
Before the laser blows up the cluster of atoms, electrons escape from their atomic orbitals and the cluster becomes a plasma. The first few electrons that are ejected simply fly away and leave behind a charged cluster of ions. However, the electrons emitted later find themselves in this charged environment that they can’t escape from.
These electrons are free to zip around, but can’t leave the cluster, and from time to time they collide with unionized atoms. They usually don’t have enough energy to free an orbiting electron from the atom they collided with, but they can excite one of the atom’s electrons up to higher energy. Ramunno found that if a second free electron collides with the same atom that had been energized by an earlier collision, it has a better chance of releasing the orbiting electron. When pairs of free electrons work together like this the cluster charges more quickly than if the laser didn’t have any help and so the cluster explodes in a shorter period of time. Ramunno calls this process Augmented Collision Ionization.
Showing posts with label Physics. Show all posts
Showing posts with label Physics. Show all posts
Saturday, March 12, 2011
Monday, March 7, 2011
Beating bromine
The problem
THE QUANTUM WORLD works quite contrary to our own concrete and everyday existence. When we are first taught about atoms, we are shown a solar system-like model with electrons orbiting the nucleus like planets orbit the sun. But physicists have known for nearly a hundred years that this picture is too simple.
Electrons are both a particle and a wave at the same time. So electrons shouldn’t just be thought of like planets, but also like a vibrating guitar string. These so-called wavefunctions can be experimentally probed and scientists understand them very well. But for more complicated molecules—combinations of more than just one atom—it becomes very difficult to directly see that theory and reality are the same.
The researcher
On top of being a professor in the physics department at the University of Ottawa, Paul Corkum heads the Attosecond Science Laboratory at the National Research Council. He is renowned for using a laser pulse to accelerate an electron out of its atom, turn the electron around, and drive it back into its orbital. When the electron recollides with the atom, short bursts of light are given off that tells Corkum about the environment in which the electron settles.
Using very short laser pulses, Corkum was able to take a high definition snap shot of the quantum cloud that defines where the electrons are around the atom.
The project
Taking high-resolution pictures of quantum orbitals is one thing, but filming a movie of the wavefunctions during a chemical reaction is another altogether. And yet, this is exactly the challenge Corkum set for his lab. Using the same technology he invented for imaging orbitals, Corkum wanted to watch a single molecule of bromine disassociate into two separate bromine atoms.
The key
Corkum blasted bromine gas with blue light. Blue is exactly the right colour to excite bromine molecules. Immediately after the blue light excites the bromine, the short laser pulse that knocks an electron out and drives it back in is shot at the gas.
Corkum saw that the blue light had not excited all the bromine molecules. This turned out to be an advantage since the resulting bursts of light from the recollision of the excited and the non-excited molecules mixed into beats.
The non-excited bromine acted exactly like a tuning fork: Corkum could use the beating between the bursts of light from molecules of bromine and from excited, separate atoms to see the difference between the two.
THE QUANTUM WORLD works quite contrary to our own concrete and everyday existence. When we are first taught about atoms, we are shown a solar system-like model with electrons orbiting the nucleus like planets orbit the sun. But physicists have known for nearly a hundred years that this picture is too simple.
Electrons are both a particle and a wave at the same time. So electrons shouldn’t just be thought of like planets, but also like a vibrating guitar string. These so-called wavefunctions can be experimentally probed and scientists understand them very well. But for more complicated molecules—combinations of more than just one atom—it becomes very difficult to directly see that theory and reality are the same.
The researcher
On top of being a professor in the physics department at the University of Ottawa, Paul Corkum heads the Attosecond Science Laboratory at the National Research Council. He is renowned for using a laser pulse to accelerate an electron out of its atom, turn the electron around, and drive it back into its orbital. When the electron recollides with the atom, short bursts of light are given off that tells Corkum about the environment in which the electron settles.
Using very short laser pulses, Corkum was able to take a high definition snap shot of the quantum cloud that defines where the electrons are around the atom.
The project
Taking high-resolution pictures of quantum orbitals is one thing, but filming a movie of the wavefunctions during a chemical reaction is another altogether. And yet, this is exactly the challenge Corkum set for his lab. Using the same technology he invented for imaging orbitals, Corkum wanted to watch a single molecule of bromine disassociate into two separate bromine atoms.
The key
Corkum blasted bromine gas with blue light. Blue is exactly the right colour to excite bromine molecules. Immediately after the blue light excites the bromine, the short laser pulse that knocks an electron out and drives it back in is shot at the gas.
Corkum saw that the blue light had not excited all the bromine molecules. This turned out to be an advantage since the resulting bursts of light from the recollision of the excited and the non-excited molecules mixed into beats.
The non-excited bromine acted exactly like a tuning fork: Corkum could use the beating between the bursts of light from molecules of bromine and from excited, separate atoms to see the difference between the two.
Sunday, January 23, 2011
Serious about solar
The problem
OIL IS EVIL. Humanity go green now. Solar panels suck. Apocalypse therefore inevitable.
The researcher
Karin Hinzer is the Canada Research Chair in Photonic Nanostructures and Integrated Devices. In 2007, Hinzer founded SunLab at the University of Ottawa, and since then has collaborated with many industrial partners. Just this year, a collaborative effort earned SunLab the 2010 Canadian Innovation Award.
The project
One such joint project is the Advancing Photovoltaics for Economical Concentrator Systems (APECS). APECS is a project that demonstrates the use of innovative technology in a practical setting. In January, Hinzer will install experimental solar panels on the roof of the Sports Complex parkade here at the University of Ottawa and at a sister site in northern California.
The key
Hinzer will use efficient gallium/arsenide(Ga/As) based multi-junction solar cells in the APECS project. Traditional silicon solar cells only absorb a small range of photons efficiently, while multi-junction cells absorb over a broader spectrum and so increase the efficiency. However, these solar cells are not cheap. APECS seeks to bring the cost down in a couple of ways.
First, Ga/As cells are usually grown on expensive germanium sheets, but Hinzer is testing Ga/As cells grown on much cheaper silicon sheets. Secondly, Hinzer is reducing the cost by getting more light to a smaller area. The way Hinzer does this is analogous to a kid using a magnifying glass to turn a normal sunbeam into a highly focused death ray for burning ants. But instead of using normal lenses, Hinzer uses waveguides that have been tested in SunLab under an artificial sun. Since the waveguides are much lighter than traditional lens systems, it won’t need the same kind of heavy-duty foundation that other big solar panels require. Therefore, it can be set on rooftops.
But having an efficient solar cell is only half the battle. If there’s only a little light shining on the solar panels, they won’t produce much electricity, no matter how efficient they are. To get around this, the modules will automatically track the motion of the sun to maximize their efficiency throughout the day. Solar panels work best when the sun’s rays are perpendicular to their surface. This is why APECS will have one station here in Ontario and a second one in California. Each panel will have an associated weather station, which Hinzer will use to compare any differences in efficiency to differences in latitude and weather.
OIL IS EVIL. Humanity go green now. Solar panels suck. Apocalypse therefore inevitable.
The researcher
Karin Hinzer is the Canada Research Chair in Photonic Nanostructures and Integrated Devices. In 2007, Hinzer founded SunLab at the University of Ottawa, and since then has collaborated with many industrial partners. Just this year, a collaborative effort earned SunLab the 2010 Canadian Innovation Award.
The project
One such joint project is the Advancing Photovoltaics for Economical Concentrator Systems (APECS). APECS is a project that demonstrates the use of innovative technology in a practical setting. In January, Hinzer will install experimental solar panels on the roof of the Sports Complex parkade here at the University of Ottawa and at a sister site in northern California.
The key
Hinzer will use efficient gallium/arsenide(Ga/As) based multi-junction solar cells in the APECS project. Traditional silicon solar cells only absorb a small range of photons efficiently, while multi-junction cells absorb over a broader spectrum and so increase the efficiency. However, these solar cells are not cheap. APECS seeks to bring the cost down in a couple of ways.
First, Ga/As cells are usually grown on expensive germanium sheets, but Hinzer is testing Ga/As cells grown on much cheaper silicon sheets. Secondly, Hinzer is reducing the cost by getting more light to a smaller area. The way Hinzer does this is analogous to a kid using a magnifying glass to turn a normal sunbeam into a highly focused death ray for burning ants. But instead of using normal lenses, Hinzer uses waveguides that have been tested in SunLab under an artificial sun. Since the waveguides are much lighter than traditional lens systems, it won’t need the same kind of heavy-duty foundation that other big solar panels require. Therefore, it can be set on rooftops.
But having an efficient solar cell is only half the battle. If there’s only a little light shining on the solar panels, they won’t produce much electricity, no matter how efficient they are. To get around this, the modules will automatically track the motion of the sun to maximize their efficiency throughout the day. Solar panels work best when the sun’s rays are perpendicular to their surface. This is why APECS will have one station here in Ontario and a second one in California. Each panel will have an associated weather station, which Hinzer will use to compare any differences in efficiency to differences in latitude and weather.
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