Tunneling Effect In Strong Laser Field

Physicists have worked on the quantum physics description of the tunnelling effect for 60 years. The group led by Ursula Keller has now for the first time succeeded in measuring time intervals that enable the direct measurement of the tunnelling time of electrons in laser-induced ionisation. No corresponding delay was measured in the experiment: something that astonished many physicists. An established but perhaps over-simplified explanatory model begins to look shaky.

Ionization of a helium atom as a "proof of principle"
of the attosecond clock: a circularly polarized laser beam
inside an electromagnetic field strikes the atom, whose
electron is split off (i.e. ionized) andis captured by a detector.
(Credit: Image courtesy of ETH Zurich)

When new technologies allow theoretical models to be tested experimentally, scientists must be prepared to say goodbye to accepted thought patterns. The current publication by Professor Ursula Keller and her team at the Institute of Quantum Electronics of ETH Zurich could bring about just such a break with accepted wisdom. The group succeeded for the first time ever in measuring experimentally the tunnelling delay times of electrons ionized in strong laser fields.

The tunnelling effect is responsible for the ability of bound electrons in atoms to pass through an energy barrier even though the barrier’s energy is higher than the electron’s binding energy. According to classical physics, overcoming this barrier is impossible, hence the assumption of a quantum-mechanical process.

A popular way of illustrating this is to imagine a ball that does not have enough momentum to surmount a hump, so simply “tunnels through” it instead. Keller says “Contrary to some accepted theories, our measurement has shown that this so-called tunnelling ionisation takes place with almost no delay. The results of her most recent experiments appear in a recent issue of the scientific journal “Science”.

For more on this laser tunneling effect......HERE