Tsunami - Beckman Institute Laser Resource Center

Mode Locking
SPM will, thus, broaden the spectrum of the pulse and provide a positive
chirp.
In order to achieve near transform-limited output pulses, it is necessary to
compensate for the pulse spreading caused by positive GVD and SPM. In
the Tsunami, this is accomplished with prism pairs in the femtosecond
regime (which provide negative GVD linear over a large bandwidth) and
with a Gires-Tournois interferometer in the picosecond regime (which
provides larger net negative GVD, but linear over a narrow bandwidth).
A
n (A)
Blue
I
Red
a-, a, a,
a
Phase Velocity =
Group Velocity = '1 (n(V - Mn/da)
Group Delay Time, Tg = (L/c)
(n(1) - adn/dh)
where L is material length
Figure A-5: Typical wavelength dependence of the refractive index of
a material.