Page 42 - Tunable Lasers Handbook
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2 Narrow-tinewidth Laser Oscillators 23
dynamics of the active medium influences the outcome in conjunction with
intracavity dispersion.
8. INTRACAVITY MULTl PLE-PRISM DISPERSION
AND PULSE COMPRESSION
In femtosecond lasers the gain and saturable absorber media introduce
group velocity dispersion (GVD) that leads to pulse broadening. The deploy-
ment of intracavity prisms allows for the compensation of GVD via the introduc-
tion of negative GVD [5 I]. This occurs because GVD is a function of the second
derivative (d2PldI.2) of the optical path length through the prismatic sequence. In
turn, (d2PldI.2) is a function of the angular dispersion of the multiple-prism array
and its derivative and can be made negative by adjusting the inter-prism distance
[52]. In general, these parameters can be expressed as [1,2,53,54]
(19)
where xl,m = tan w~,~,. These equations are general and enable the design of any
multiple-prism array for pulse compression. In this regard, the equations can be
applied to one, two, four, six prisms or more [51,52,55-571 (Fig. 7). Further, the
equations can be utilized to provide a numerical description of intracavity dis-
persion in generalized prismatic arrays as a function of angular and/or beam
deviations [54]. The use of these multiple-prism arrays in femtosecond dye laser
cavities is discussed in Chapter 5.
For the special case of a single prism deployed at Brewster's angle of inci-
dence, the equations reduce to the case discussed by Fork et al. [52]:
