William Angerer - Department of Physics and Astronomy - University ...

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After polarization, the beam was amplitude modulated with a standard optical
chopper (1 kHz) and a sequence of optics were used to direct the beam to a beam
splitter which transmitted ,,-,90% of the fundamental light to the sample. The remaining
10% of the Ti:Ah03 pulse was reflected and propagated along an identical
optical line containing a quartz wedge. This line was used to normalize the nonlinear
optical signal, which will be described in greater detail in a following paragraphs. The
sample was placed at the focal point of an fj 4.0 achromatic lens which focused the
4 mm beam to 100 J.Lm spot. The achromatic lens has a Rayleigh range of 4 mm which
ensured that the spot size of the beam did not vary significantly as the wavelength
of the fundamental beam was scanned. Any second-harmonic signal generated along
the beam path prior to the sample was removed with a low pass optical filter.
Interaction of the ultrafast Ti:Ah03 laser pulse with the sample or quartz produced
a second-harmonic generation pulse with angular frequency 2w. The SHG
pulse was separated from the fundamental pulse by high pass filters and a Jarrel Ash
:\Ionospec 18 monochrometer with entrance and exit slit widths of 2 mm. This slit
configuration has a top hat transmission function with a full width wavelength bandwidth
of ~,,\
= 10 nm. The monochrometer grating was blazed at 500 nm to maximize
sensitivity to near IR frequency doubled light. In addition, the SHG signal was pol::trized
to probe various second-order susceptibility elements. The SHG signal was
detected by a Hamamatsu R943-02 photomultiplier tube. The R943-02 is a high
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