I am very keen to control transition probability for deexcitation of excited states. Normally there is no control over deexcitation, they compete depending upon population of excited states created. I want to hold on deexcitation- say by a control exercised through application of fields or any other simple idea.
Some metastable atoms (for example hydrogen atom H 2s) can be transferred to a resonant level (H 2p) under applied electric field. The electron-impact cross sections for H 2s and H 2p have been measured separately long time ago basing on this effect.
OK, let me elaborate a bit further what I need. Can we trap the states in a local minima (how to create these is also a question) to prevent them from self de-exciation, rather use other means of triggering to bring them to the minimum energy condition. This holding has to be any prolonged time.
You can choose some meta stable states of particular life time. And de-excitation from meta stable states can be controlled by using the pressure or density of the ambient gas present. This may not exactly hold the de-excitation, but it will help in controlling the de-excitation from the meta stable states. I think this idea can be used to hold other states also provided that state is having lot of radiative decay from this particular meta stable state. You can see the reference:
Energy pooling collisions in barium
J. A. Neuman, A. Gallagher, and J. Cooper
PHYSICAL REVIEW A VOLUME 50, NUMBER 2 AUGUST 1994
The question is what are your objects and what are the states/levels you want to to control. For example, it's possible to populate certain metastable states using tunable laser (as it is done in ZEKE/ZEKE PFI spectroscopy), but these ones might be not the states you are interested in.
It's a more challenging task if you want to take a "normal" state, which usually has a short lifetime and force the system to stay long in this state (actually, it won't be the same system anymore - imagine changing the potential surface to create a local "well").
I'm not sure if I understood you correctly, but
there is a theoretical paper on the control of the excited state population of adenine in water (DOI: 10.1039/c2cp24002e)
Let me consider a hypothetic situation. We have three energy levels E1 < E2 < E3. States |1> and |3> have the same parity so the dipole transition is forbidden. At the beginning, states |1> and |2> are fully occupied whereas state |3> is empty. Let's pump the upper state |3> continuously and resonantly from the middle state |2> with laser photons of energy E3-E2. Both, excitation and deexcitation occur between these states. At the same time we start pumping the middle state |2> continuously and resonantly from the lowest state |1> with another strong laser at photon energy of E2-E1. Will the increased population of state |2> lead to a reduced deexcitation from the upper state |3>?
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