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

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7.2.1 Optical Setup
The optical path of the laser light in the microscope is shown in Fig. 7.2. A modelocked
800 nm pulse from the Ti:Ah03 laser was collimated by a lens and enlarged
by a telescope. The beam was then polarized and amplitude modulated by an optical
chopper. A series of optics directed the fundamental beam to a 0.85 NA air coupled
objective. Prior to this objective, a small fraction of the fundamental light was reflected
to a reference nonlinear line containing a plate of phased matched KDP and
a photomultiplier tube.
The objective focused the fundamental beam to a ",3 pm spot on a sample placed
at the focal point of the objective (about 0.3 mm from the front of the objectiye).
The intense fundamental light induced the emission of SH photons from the sample.
The signal was emitted in reflection from the sample surface and was collected by the
objective. The objective also collected the reflected fundamental light. Because the
sample was positioned at the focal point of the objective, the reflected SHG light and
the fundamental light propagated as collimated beams along the same path as the
incident fundamental beam.
After exiting the objective, the SHG beam was reflected by a harmonic beamsplitter,
which was engineered to reflect light at a wavelength of 400 nm and transmit
light at a wavelength of 800 nm. In practice, a small fraction of the fundamental
light was also reflected from the harmonic beamsplitter and propagated with the
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