Dark state

A dark state in an energy level of the physics of an atom or molecule, which is undesirable in certain applications in laser spectroscopy, such as laser cooling. These states are as dark- called because the atoms are in this state for the desired application will be "invisible". However, there are exceptions where the existence of dark states is explicitly used ( eg certain types of atomic clocks ), but is then usually not spoken of dark states.

Physical Basics

In laser spectroscopy particles are excited by lasers and detects the emitted light. Excited particles go by emitting a photon by either spontaneous or stimulated emission returns to an energetically more favorable state. In the spontaneous emission, it is possible that the particles do not fall back into the state in which they were before the laser excitation. Which transitions are possible is determined by the selection rules. When a particle passes into such a state, it can not be re-excited by the laser - the particle is dark for the laser.

Countermeasures

The particles may be in a dark state can be brought only by a further laser, is resonant with the dark state to the desired state. Such a laser is known as " pump-back laser " or in English " repumper ".

Postgraduate

• Introduction to coherent dark states

• Spectroscopy