Optical Damage Threshold of Silicon for Ultrafast Infrared Pulses Page: 3 of 7
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InGaAs diode -To boxcar, DAQ
Wedge beam sampler
Sample and knife edges mounted
on motorized xand ytranslation
CaF2 final focus Sample
lens on z and x
Pellicle beam samplers
Beam stop on
FIGURE 1. Schematic of the damage threshold measurement experiment.
sample was mounted vertically on motorized translation stages with motion in the plane
of the sample. The sample was oriented during initial setup so that it was parallel to the
directions of motion of the stages. Razor blades were mounted in the same plane as the
sample to conduct knife-edge transverse spot size measurements. A photograph of the
setup is shown in Figure 2.
For each wavelength tested, the infrared beam was first coupled via fiber to an optical
spectrum analyzer (OSA) to confirm that no residual light at shorter wavelengths was
present. Such light could have come from the Ti:sapphire pump at 800 nm or in the
visible range from the pump mixed with the signal or the idler within the OPA. Next,
an autocorrelation trace was taken to measure the pulse duration. Then, the final focus
lens was adjusted to place the beam waist just in front of the sample surface. This was to
ensure that maximum fluence occurred on the sample surface rather than in the bulk, so
that the transverse spot-size measurements would yield relevant results. Also, the HeNe
beam was spatially overlapped with the infrared pulses and one damage spot was created
to confirm that pulse energy was sufficient and the focus was tight enough for damage to
occur. Once this was complete, the transverse spot sizes were measured using the knife-
edge technique. As a final setup step, the sensitive pyroelectric detector used to measure
pulse energy was calibrated against an Ophir Optronics PE10 energy detector.
Once the setup was complete for a particular wavelength, damage data were taken. For
each event, the pulses were allowed to illuminate the sample by removing a beam stop,
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Cowan, B. Optical Damage Threshold of Silicon for Ultrafast Infrared Pulses, article, September 7, 2006; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc882699/m1/3/: accessed April 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.