ATTOSECOND SCIENCE

• Attosecond science is the study of superfast processes using extremely short light pulses.
• These pulses are so short that they can be used to capture the motion of electrons in atoms and molecules.
• To understand how attosecond science works, it is helpful to compare it to photography.
• A digital camera captures images by recording the light that is reflected off of objects. To capture a clear image, the camera needs to have a short shutter speed.
• This is because if the shutter speed is too long, the image will be blurred due to the movement of the object being photographed.
• Imagine a hummingbird's wings beating. To capture a single beat with a digital camera, you would need a shutter speed of 1/80th of a second.
• This is because the human eye can see up to 60 frames per second, but it cannot see a single wingbeat as it happens.
• The same principle applies to attosecond science. To capture the motion of electrons, attosecond scientists need to use light pulses with a very short duration.
• These pulses are so short that they can capture the motion of electrons in real time.
• Attosecond science has a wide range of potential applications. For example, it can be used to develop new types of lasers and other light sources, as well as new types of detectors and materials.
• Attosecond science can also be used to study the dynamics of electrons in atoms and molecules, which could lead to new insights into the fundamental nature of matter.

• The fascinating world of attosecond pulse generation finds its roots in wave mechanics.
• In the year 1988, Anne L’Huillier, along with her colleagues in Paris, embarked on a pioneering journey. Their experiment involved passing an infrared light beam through a noble gas, which led to an astonishing discovery.
• As the light beam interacted with the noble gas, an extraordinary phenomenon unfolded.
• The gas emitted light waves whose frequencies were not mere replicas of the incident beam's frequency. 
• Instead, they were high multiples of it. For instance, if the frequency of the initial beam measured 10 arbitrary units, the emitted light showcased frequencies of 50 units, 60 units, 70 units, and so forth.
• This remarkable occurrence is known as a high-harmonic generation, and the resulting waves are termed overtones of the original.
• Further exploration by the research team revealed an intriguing pattern. As they gradually increased the frequency of the initial beam, the intensity of the emitted light exhibited distinct behaviour.
• Initially, it dropped sharply, then reached a plateau where it remained relatively constant for a certain range of frequencies, before declining once more.
• By the year 1994, researchers had unravelled the underlying mechanisms responsible for these effects.
• It was revealed that a beam of light is characterized by oscillating electric and magnetic fields.
• The term 'oscillating' denotes that these fields undergo continuous cycles of strengthening and weakening at a particular point.
• This oscillation of electric and magnetic fields played a pivotal role in the interaction with electrons.
• At points along this oscillatory path, electrons experienced alternating influxes and withdrawals of energy.
• When energy was imparted, electrons momentarily broke free from their atomic bonds.
• Subsequently, as energy was taken away, these liberated electrons recombined with their parent atoms, releasing surplus energy in the form of emitted light.
• To complete the puzzle, researchers turned to the intricate equations of quantum mechanics.
• These equations not only offered a coherent framework to describe the entire journey of electrons but also provided profound insights into the behaviour of the emitted light.
• They elucidated why the intensity of the re-emitted light plateaued as the frequency of the incident beam was increased.

• To produce an attosecond pulse, a high-intensity infrared laser beam is focused on a noble gas.
• This ionizes the gas atoms, creating free electrons. The free electrons are then accelerated by the laser field.
• When the accelerated electrons collide with the parent ions, they emit photons of high energy.
• The frequency of these photons is a multiple of the frequency of the laser pulse, and the pulse duration is typically a few attoseconds.
• The intensity of the emitted photons plateaus as the laser frequency is increased. This is because the electrons are unable to keep up with the rapidly oscillating laser field.
• To fine-tune the setup to produce light pulses for a few hundred attoseconds, physicists combine a large number of overtones.
• Overtones are multiples of the laser frequency. When the peak of one overtone merges with the peak of another, it undergoes constructive interference and produce a larger peak.
• When the peak of one overtone merges with the trough of another, they undergo destructive interference and cancel each other out. These pulses are produced only when the beam's frequency is within the plateau range.

Attophysics is a rapidly developing field with a wide range of potential applications. Some of the potential applications of attophysics include:

• Attosecond pulses can be used to study the motion of electrons in atoms and molecules in real-time. This could lead to new insights into the fundamental nature of matter and could also be used to develop new materials with unique properties.
• In 2010, Krausz's team used attosecond pulses to study the photoelectric effect in neon atoms. They found that electrons leaving two slightly different energy levels in a neon atom do not do so simultaneously, as was once thought. Instead, there is a 21-attosecond delay. This finding could lead to a better understanding of the photoelectric effect and could also have implications for the development of new solar cells.
• Attosecond pulses can be used to develop new types of lasers and other light sources. These light sources could have a wide range of applications in medicine, materials science, and other fields.
•  Attosecond pulses can be used to develop new types of detectors. These detectors could be used to study a wide range of ultrafast phenomena, such as the dynamics of chemical reactions.
• Attosecond pulses can be used to develop new materials with unique properties. For example, attosecond pulses could be used to create materials that are more efficient at conducting electricity or that are stronger and lighter than existing materials.

8. Conclusion