Abstract
A theoretical model for the ultrashort-pulse (USP) generation by lasers with saturable absorbers is presented. The gain medium is assumed to be a two-level system whereas the absorber is described by a four-level system which is characterized by a two-stage absorption process and the pertinent relaxation times. Laser dynamical equations are developed in the rate-equation approximation and boundary conditions appropriate for an unidirectional ring cavity are established. Evolution of USP is investigated for different combinations of parameter values appropriate for solid-state laser systems by computer simulation, employing a finite difference approximation for the dynamical equations. It is shown that USP output is attainable even if the cross-section of the excited-state absorption isgreater than that of the ground-state absorption and the laser is operating just above threshold. In fact, it is found that through the participation of a strong excited-state absorption the discrimination against satellite pulses is enhanced so that single-pulse output is more achievable. Furthermore, it is proposed that single picosecond pulses may be obtainable from relatively broad initial peaks by utilizing the high pulse-selection and pulse-shortening efficiency of the absorber due to the contribution of the excited-state absorption. The applicability of the present model to singlet-triplet crossing and photoisomer formation is also discussed.
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References
P. G. Kryukov, V. S. Letokhov: IEEE J. QE-8, 766 (1972)
V. S. Letokhov: Sov. Phys. JETP28, 562 (1968)
J. A. Fleck, Jr.: J. Appl. Phys.39, 3318 (1968)
For a detailed review see S. L. Shapiro (Ed.)Ultrashort Light Pulses, Topics Appl. Phys.18, (Springer, Berlin, Heidelberg, New York 1977)
M. Hercher: Appl. Opt.6, 947 (1967)
M. Hercher, W. Chu, D. L. Stockman: IEEE J, QE-4, 954 (1968)
L. Huff, L. G. DeShazer: J. Opt. Soc. Am.60 157 (1970)
C. R. Giuliano, L. D. Hess: IEEE J QE-3, 368 (1967)
D. N. Dempster, T. Morrow, R. Rankie, G. F. Thompson J. Chem. Soc. Faraday (II)68, 1479 (1972)
B. K. Garside, T. K. Lim: J. Appl. Phys.44, 2335 (1973)
See, for example, W. F. Ames:Nonlinear Partial Differential Equations in Engineering Academic Press, New York 1965)
G. H. C. New, K. E. Orkney, M. J. W. Nock: Opt. Quant. Elect8, 425 (1976)
R. G. Harrison: J. Phys. D8, L203 (1975)
E. P. Ippen, C. V. Shank, A. Dienes: Appl. Phys. Lett21, 348 (1972)
F. O'Neill: Opt. Comm.6, 360 (1972)
D. J. Bradley: Opto-Electronics6, 25 (1974) (and references cited therein)
B. K. Garside, T. K. Lim: Opt. Comm.12, 240 (1974)
D. von der Linde: Appl. Phys.2, 281–296 (1973)
F. P. Schäfer (Ed.):Dye Lasers Topics Appl Phys.1 2nd rev. ed. (Springer, Berlin, Heidelberg, New York 1977)
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Work supported in part by the National Research Council of Canada under grant No. A6005.
This author is now with Welwyn Canada Limited, London, Ontario, Canada.