|
Description:
|
Laser -atom interactions create atomic coherence and large nonlinear atomic polarization .
We investigate resonant laser -atom interactions to generate large nonlinearities
and control them using magneto -optical fields . Coherent control of high -order
susceptibilities and magneto -optical rotation are demonstrated . Experiments are supported
by theoretical studies that effectively describe the observed phenomena .
It is shown that a new coherent field , with polarization orthogonal to a weak
signal field , can be parametrically generated via an all -resonant four -wave -mixing
process . This is demonstrated in a double -ladder system having two intermediate
states between a ground and an excited state . It is shown that the parametricgeneration
process can be coherently controlled by coupling lasers and magnetic fields .
It is theoretically established that the underlying physics is a resonant three -photon
process with a wide domain of control parameters .
Electromagnetically induced transparency (EIT ) , where absorption of a weak
probe is suppressed via quantum interference , is demonstrated in a usual three -level
ladder system . It is observed that in contrast with EIT in a usual ladder system ,
addition of a second channel helps to suppress the absorption of two weak probe
fields in the double -ladder system . The resulting enhancement of transmission in two
different channels is due to gain caused by three -photon processes .
Coherent control is strongly limited by coherence lifetime , which is the inverse of
the dephasing rate . A lambda -system , having two ground states coupled to a common
excited state by lasers , can generate a new eigen (dark ) -state that is transparent to incoming fields and hence suppresses fluorescence . However , ground -state dephasing
perturbs the dark state . A new method for measuring the ground -state dephasing
rate from fluorescence signals is proposed and a proof -of -principle experiment demonstrated .
While two laser fields in a lambda -system are resonant with their respective
transitions , the atomic polarizations are very sensitive to an applied magnetic field .
This effect can be used for optical magnetometry . The degree of sensitivity of the
magnetometer is determined by two competing parameters–atomic density and laser
intensity . It is shown experimentally that the optimal sensitivity reaches saturation ,
which is contrary to the idea that sensitivity increases indefinitely with an increase
in the above parameters . |