CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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μJ has a very high peak power. Under this high intense regime refractive index is a function
of light intensity. For a Gaussian pulse, temporal intensity profile can be described by
I I
o
2
t
exp
2
(2.18)
An intense pulse with a Gaussian profile leads to phase change which in turn changes the
frequency and broadens the pulse. Additionally the nonlinear interaction introduces a
frequency chirp i.e. for a positive nonlinear refractive index leading edge of the pulse is
downshifted in frequency. In our system white light is generated by focusing ~ few μJ 800nm
pulse on 1.5mm sapphire thick plate as shown in the below given schematic.
Figure 2.11. Schematic of a WLG in set up used for present studies.
2. 8. 5. Laser diagnostics
The pulse obtained after compression is diagnosed by Autocorrelator to obtain its time
profile. The schematic of an autocorrelator is given in the figure 2.12. The input beam is split
into exactly 2 equal parts where one of beams moves through an optical delay and they are
made to converge at a SHG crystal. Since efficiency of SHG is directly proportional to the
intensity. In the present study we used a model ASF-20 autocorrelator for pulse width