Self-induced transparency phenomena of single-mode pulse laser propagatingin a thick ytterbium vapor column

The variations in pulse shape of a single-mode pulse laser propagating thro ugh ytterbium (Yb) atomic medium were investigated experimentally. The lase r pulse shape was changed as a function of pulse area and it could be expla ined well using the area theorem. When the pulse area was close to 2 pi, th e pulse shape was transformed to a hyperbolic secant function after transmi ssion. The transmission curve of the propagating laser vs. the pulse area d emonstrated self-induced transparency phenomena well. However, the transmis sion was markedly reduced when the atomic density was increased above simil ar to 4 x 10(10) atoms/cm(3). Several causes; such as collision-induced pol arization relaxation, Doppler broadening, laser incoherence, and power broa dening, which could induce reduced transmission, were examined. It was the incoherence of the laser that caused reduced transmission because the laser line width was broader than the Fourier-transform limit, and the absorbed energy dissipated through spontaneous emission.