(c) Dr Paul Kinsler. [Acknowledgements & Feedback]
LOCATION: Photon'02, Cardiff, U.K., 2002: oral presentation.
WORK DONE AT: Physics Department, Imperial College.
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AUTHORS: P Kinsler, G.H.C. New
Optical parametric oscillators (OPOs) based on aperiodically-poled lithium
niobate (APPLN) have generated 53 fs idler pulses at 3m that are nearly
transform limited, and contain only five optical cycles; laser pulses with
less than three optical cycles have been generated in other contexts.
This means the slowly-varying envelope approximations
traditionally used to model such processes are no longer
valid. Building upon the ideas of Brabec and Krausz, we present
a comprehensive framework for treating the
optical parametric interaction for few-cycle pulses.
We apply the theory to an OPO model that includes
dispersion, multiple fields and its second-order nonlinearity.
We show numerical simulations involving pulses with different numbers of
cycles, including idler pulses containing as few as two cycles. The
characteristic differences between the results under various levels of
approximation are discussed in detail. These demonstrate how the effect of
the nonlinearity differs between the many-cycle and
few-cycle cases, and how the commonly used slowly varying envelope
approximation fails as pulse lengths decrease.
 T. Beddard, M. Ebrahimzadeh, T.D. Reid, W. Sibbett, Opt.Lett. 25, 1052 (2000).
 A. Baltuska, Z. Wei, S. Pshenichnikov and D. Wiersma, Opt.Lett. 22, 102 (1997).
 T. Brabec, F. Krausz, Phys. Rev. Lett. 78, 3282 (1997).