Suppression of excited-state absorption in laser crystals

P. Le Boulanger, J.-l. Dorralan, S. Girard +1 more

Elena Kuznetsova, Roman L. Kolesov, Olga A. Kocharovskaya

A method of suppression of losses due to excited-state absorption (ESA) in laser crystals is proposed, based on the well-known phenomenon of electromagnetically induced transparency. Typical situations in which ESA prevents lasing are considered. Theoretical analysis shows that by using an additional driving laser field one can inhibit ESA and make lasing possible. On the basis of available spectroscopic information estimates for rare-earth-ion-doped laser materials are presented. They show the feasibility of obtaining optical gain at parity-allowed $4{f}^{n}\ensuremath{\leftrightarrow}4{f}^{n\ensuremath{-}1}5d$ transitions of rare-earth ions in the ultraviolet spectral region after suppression of ESA at an emission wavelength into the conduction band of a host material.

М. P. Kulish

Elena Kuznetsova, Roman L. Kolesov, Olga A. Kocharovskaya

We consider the coherent population trapping effect with a train of ultrashort pulses in a $\ensuremath{\Lambda}$-type system with two bound states and a continuum replacing the upper state. Population transfer to the continuum can be totally suppressed provided that the splitting between the bound states is a multiple of the pulse repetition rate. Compared to the traditional case with only two laser fields coupling the bound states to the continuum, CPT with a pulse train allows one to avoid incoherent population losses due to interaction of the fields with ``wrong'' transitions, which results in only partial suppression of ionization. A method of suppression of excited-state absorption of pumping radiation in laser crystals, with pumping in the form of the pulse train, is proposed. As a particular example pumping dynamics of a ${\mathrm{Ti}}^{3+}:{\mathrm{YAlO}}_{3}$ crystal using this technique is numerically analyzed.

Donald E. Cooper

Ахмеджанов Ринат Абдулхаевич, A. A. Bondartsev, Л. А. Гущин +1 more

This paper shows that the satellite lines that appear in the absorption and fluorescence spectra of neodymium ions in a LaF3 crystal at concentrations of about 0.5 at.% and the accompanying lines of the isolated ion are caused by pairwise interaction of the Nd3+ ions. Double optical resonance is used to study the structure of the satellite lines in the neighborhood of the 4I9/2→4G5/2 transition of the isolated ion (wavelength 5777.1 Å), hidden by inhomogeneous broadening. When neodymium ion pairs are excited by resonance laser radiation, the presence of anti-Stokes components is recorded in the fluorescence spectrum (up-conversion). It is shown that the main up-conversion mechanism is cumulative pair excitation. These results are convincing evidence that the suppression of absorption from excited levels can be experimentally observed in condensed media.