MODULATION EFFECTS OF LASER CHARACTERISTICS ON 3-COLOR, 3-STEP, 3-PHOTON IONIZATION OF YB-168

Modulation effects of laser pulse profiles and bandwidths, as well as detuning effects of laser frequencies on the population dynamics and t he ion yield are examined for a 3-color, 3-step, 3-photon ionization s cheme of Yb-168 in the framework of the Bloch equation. For incorporat ing the bandwidth effect quasi-monochromatic single-mode laser pulses are taken to interact with the systems and the pulse spectra are descr ibed by sets of phase-independent modes. It is found that highly effic ient photoionization occurs when Gaussian-pulsed monochromatic lasers are tuned to the frequencies giving rise to the population inversion. It is remarkable that when the quasi-monochromatic lasers photoionize the system, the ion yield is much larger in the Gaussian case than in the square pulse case; i.e. pulse-shape modulation plays an important role for enhancing the ionization efficiency.