We report the first observation of photon echoes in an organic mixed crystal. The echo was observed after excitation with a nitrogen-laser-pumped dye laser in the $^{1}B_{2\mathrm{u}}\ensuremath{\leftarrow}^{1}A_{g}$ electronic transition at 3739.9 \AA{} of pyrene in biphenyl at 2 K. The photon-echo excitation spectrum of the origin (zero-phonon line) region shows that drastic variations occur in the coherence lifetime of sites which, qua incoherent (fluorescent) decay, are indistinguishable.We report the first observation of photon echoes in an organic mixed crystal. The echo was observed after excitation with a nitrogen-laser-pumped dye laser in the $^{1}B_{2\mathrm{u}}\ensuremath{\leftarrow}^{1}A_{g}$ electronic transition at 3739.9 \AA{} of pyrene in biphenyl at 2 K. The photon-echo excitation spectrum of the origin (zero-phonon line) region shows that drastic variations occur in the coherence lifetime of sites which, qua incoherent (fluorescent) decay, are indistinguishable.

Physical Review LettersJun 7, 197672 citations

Combined effect of Stark and singlet-triplet mixing on photon-yield spectra of singly excited helium

A. Mihelič, M. Žitnik, Kevin Charles Prince +2 more

We present a theoretical framework for the calculation of photon-yield spectra from radiative-cascade decays of photoexcited helium atoms in a static electric field for incident photon energies below the first ( $N=1$ ) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the $1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P$ states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.We present a theoretical framework for the calculation of photon-yield spectra from radiative-cascade decays of photoexcited helium atoms in a static electric field for incident photon energies below the first ($N=1$) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the $1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P$ states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.

Physical Review AFeb 22, 20123 citations

N=1

) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the

1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P

states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.