(c) Dr Paul Kinsler. [Acknowledgements & Feedback]
This work was done in conjunction with Prof. GHC New in the Department of Physics at Imperial College.
This description is under construction
Optical parameric ocillators (OPO's) based on aperiodically poled
lithium niobate (APPLN) can generate
53fs nearly transform limited pulses at 3
m corresponding to only
five optical cycles[1]. Such short pulses are usually modelled by traditional
slowly varying envelope approximations (SVEA), but in order to obtain a
more accurate picture a new
approach is needed. Ultrashort pulses
have applications in areas ranging from precision spectroscopy
(THz to VUV), optical atomic clocks, and fundamental tests of
physical theories.
I have derived a general equation for treating (short) few-cycle pulses
based on
the approach of Brabec and Krausz [2] (see also [3]). We allow for
diffraction,
multiple fields, and also the
nonlinearity present in an OPO. The results of numerical
simulations of an OPO using this new method
will be compared to the SVEA solution, and the characteristic differences
between the two are discussed. We also aim to compare results with a
modified SVEA method, which attempts to simulate few-cycle effects by
the addition of a variable phase adjustment to the pulse envelope.
My derivation has been done in such a way as to avoid approximation until the final step, and this allows a rigorous investigation of exactly {\em what} approximations need to made in order to obtain a convenient method for solving these types of few-cycle-pulse problems. It also allows the choice of which approximations to make, and a decision as to what order of approximation to use to be made. I plan to make to make my full step-by-step derivation publically available, as well as a suitable version of my pulse simulation code.
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Date=18 20011117 Author=P.Kinsler Created=20011117