9C3 - The influence of Nd3+ion properties in a glass matrix on the dynamics of a Q-spoiled laser

Abstract

Due to the different environments, the fluorescence line of Nd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> in glass can be considered as the envelope of the different fluorescence lines of the ions. It is a typical example of an hlhomogeneously broadened line. One can conceive that energy can be transferred between ions of different energy spectrum. Our observations seem to confirm such a cross-relaxation process. In particular, the emission linewidth of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -spoiled laser (about 20 Å at 3 dB below maximum) changes very little with respect to the emitted energy in contrast to the spectral width, over which the fluorescence intensity drops sharply due to laser action, which depends upon the laser output energy. This spectral width is very much larger than the emitted spectrum (a few hundreds of angstroms). The lifetime of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{11/2}</tex> level, the terminal level of laser action at 1.06 μm, has never been measured so far. A possible 5 μm fluorescence from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{11/2}</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{9/2}</tex> would be absorbed by the glass. During <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched laser action, there is evidence that the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{11/2}</tex> level becomes rapidly populated through stimulated emissions from the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4F_{3/2}</tex> level. This <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{11/2}</tex> population decreases as the pulse duration increases from 25 to 90 ns which indicates a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{11/2}</tex> lifetime of order of magnitude a few tens of nanoseconds. A calculation was made according to the model of Lengyel and Wagner. A fourth level with a finite lifetime was introduced in their three-level system. The experimental data is in qualitative agreement with the prediction of this simplified theory, but does not allow more than an order of magnitude estimate of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4I_{11/2}</tex> lifetime.