Electronic observation directly tunneling

Professor Ferenc Krausz , leader of the research team

A strong electric field from a strong laser pulse can cause the electron to tunnel out of the atom within a millionth of a second.

Recently, German physicists have for the first time observed this quantum mechanical effect as derived from real time. This jump will pave the way for a new technique that can probe short-lived states of atoms or molecules that can give direct information about electron tunneling kinetics. (These results have just been published in Nature ).

A laser pulse contains a small amount of electric field vibrations that can pull electrons at the outer layer of atoms away from the nuclear link. At the oscillating peak, the outer layer electron can be pulled so that the electron can escape (or tunnel) out of the atom, even if the electron has enough energy to escape the gravitational pull of the particle. multiply. But this effect occurs so quickly that current devices can only observe the final state of ionized atoms, but cannot see any intermediate states.

Ferenc Krausz and colleagues from Max Planck Institute for Quantum Optics have found a way to improve that limitation by exploring atoms with two laser pulses with different wavelengths to be able to adjust one. how to take a quick snapshot of the tunneling process. This technique involves probing atoms that have tightly bound electrons, for example rare gases, which in this case use Neon - which is difficult to be ionized by a single laser pulse. Atoms are processed by stimulation by a laser pulse, pushing the outer electrons of the atom to the position where it can perform tunneling with ionizing pulses.

Principle of electronic level transfer (According to Nature 446 (2007) 627).

In the second process, if the excitation pulse has a much shorter wavelength than the ionization pulse, it can be reversed at various periods in the period of the ion ion pulse and only at these points can the electron be ability to jump to the possible point for tunneling. And by recording the process of electron tunneling in the cycle of ionization pulses, a picture of the electron slowly escaping from the atom can recover.

In the experiment, two pulses must be synchronized to the correct level a few millionths of a second to create accuracy. To overcome this obstacle, Krausz and the team used from an infrared laser to produce both pulses. First, they project a laser pulse through a gas nozzle to produce a very short laser pulse of the ultraviolet region. This pulse will arrive at the sample of Neon atoms with the original pulse delayed. Finally, a mirror system was used to alter the delay of this pulse, and physicists were able to record the electronic tunneling process with a time resolution below the femto-induced level (10- 15 s).

Electronic probability can tunnel (According to Nature 446 (2007) 627).

According to quantum theory, the probability of an electron tunneling through a potential barrier will increase in a stepwise fashion with the peak of the ionizing pulse. And today, Krausz's group has confirmed this for the first time. Today's induction lighting tunneling technique can be used to improve the observations of electron displacement, giving scientists unprecedented visions of precursors in areas such as micro electronic, or biological photography."There may still be many problems with transient states that we still cannot capture," said Jonathan Marangos, a femtosecond technology expert on PhysicsWeb - "And this technique can help we do that ".

The Doctrine of Independence