INVERSIONLESS AMPLIFICATION OF RADIATION - COMPARISON OF SCHEMES WITHAUTOIONIZING AND AUTOIONIZING-LIKE OPERATING LEVELS

Two three-level inversionless schemes for amplification of radiation a re considered and compared. One scheme involves two close-lying autoio nizing (AI) states as upper operating levels. The gain in this scheme can be rather large if the two selected AI states satisfy the followin g conditions: (a) they decay into the same continuum, (b) one or both AI states have large Fano parameters, and (c) the spacing between thes e levels is comparable with their autoionizing widths. Upper operating levels of the second scheme are discrete. Coherence between them is f ormed by Raman-type transitions via continuum states in a strong drivi ng electromag netic field (laser-induced AI states). The driving-field -ionizing widths of the upper levels play the role of the netic field (laser-induced AI states). The driving-field-ionizing widths of the up per levels play the role of the autoionizing widths in the previous sc heme. They can be varied by changing the intensity of the driving fiel d. Conditions under which the gain has its maximum are found for both schemes. Linear and nonlinear regimes of amplification are investigate d. Advantages of both schemes are discussed.