Attosecond science is a branch of physics that deals with light-matter interaction phenomena, production of extremely short light pulses and using them to study superfast processes.

The Physics

• Wave mechanics- The concepts underlying the production of attosecond pulses come from wave mechanics.
• In 1988, Anne L’Huillier and her colleagues passed a beam of infrared light through a noble gas which emitted light in a high multiple frequency of the beam’s frequency.
• The emitted waves are said to be overtones of the original.
• The researchers also found that as the frequency of the original beam increased, the intensity of the emitted light dropped sharply, then stayed constant for a range, and then dropped again.
• Studying the light - A beam of light consists of oscillating electric and magnetic fields.
• ‘Oscillating’ means that at a given point, the field’s strength alternately increases and decreases. So an electron at this point would be imparted some energy and then have it taken away.
  • When energy is imparted- The electron would come loose from an atom.
  • When the energy is taken away- The electron and the atom would recombine, releasing some excess energy.
• This energy is the light re-emitted by the gas.
• Quantum mechanics- The researchers also found a way to describe this process using the equations of quantum mechanics.

Production

• Multiple overtones- When the infrared beam strikes the noble gas atoms, it produces multiple overtones.
  • Constructive inference- If the peak of one overtone merges with the peak of another, they undergo constructive interference (like in the double-slit experiment) and produce a larger peak.
  • Destructive Inference-When the peak of one overtone merges with the trough of another they cancel themselves out.
• Light pulses- By combining a large number of overtones in this way, physicists could fine-tune a setup to produce light pulses for a few hundred attoseconds due to constructive interference and then stop, due to destructive interference.
• These pulses are produced only when the beam’s frequency is within the plateau range. 

What have they done?.

• RABBIT- It is developed in 1994 by Pierre Agostini and his colleagues which is a major technique to measure the duration of a short light pulse.
• The attosecond pulse and another pulse of a longer duration are shined on atoms of a noble gas.
• The photons in the two pulses kick out electrons from the atoms.
• Physicists harvest data about these electrons and the atoms which also gives information about the pulse’s properties including its duration.
• Attosecond pulses in train- It was only in 2001 that Agostini et al. and Ferenc Krausz et al. were able to produce verified attosecond pulses in a train.
• Pulses in a train refers to a pulse followed by a gap, followed by a pulse, and so forth.
• Short attoseconds- After these achievements, all three groups, and other physicists, kept refining these techniques so that, by 2017, experts were able to produce a pulse as short as 43 attoseconds.

An attosecond is an astonishingly short unit of time, equivalent to one quintillionth of a second (1×10−18 of a second) or one-billionth of a nanosecond. To put this into perspective, if a second were stretched to cover the entire age of the universe, which is approximately 13.8 billion years, an attosecond would be just a fraction of a second. The fundamental significance of attoseconds in physics lies in their ability to shed light on phenomena that were previously hidden from our view. These extremely short time intervals are relevant in the fields of ultrafast optics and laser physics, particularly when studying the behavior of electrons within atoms and molecules.

• Applications:
  • Attosecond physics allows scientists to look at the very smallest particles at the very shortest timescales.
  • At this timescale, researchers can now capture the dynamics of electrons within atoms and molecules, allowing them to witness the incredibly fast processes that govern chemical reactions and electronic behavior.
  • Attosecond pulses:
    • One of the most groundbreaking applications of attosecond science is the ability to create and manipulate extreme ultraviolet (XUV) and X-ray pulses, which are vital for imaging ultrafast processes at the atomic and molecular scale.
    • These pulses are produced using high-intensity laser systems that generate attosecond bursts of light.
    • With these attosecond pulses, scientists can "freeze" the motion of electrons within atoms and molecules, providing a real-time view of electron movement during chemical reactions.
    • The Attosecond pulses can be used to test the internal processes of matter and to identify different events.