Diploma thesis

Gaussian functions. The result is a Gaussian distribution doubled in width and
doubled in central frequency:
I3(ω3) = K ′ e − (ω 3 −2ωp)2
4σ 2 p . (4.8)
With this formula, we can now map our measured pump data points into the expected
SHG spectrum by a simple transformation:
I(λp) → I
� �2 λp
, I(ωp) → I(2ωp)
2
2 . (4.9)
If we approach the phasematching, this formula is not valid any more. A numerical
simulation of this mapping without simplifications is displayed in Figure 4.14. As
plotted, the sinc function determines the conversion efficiency from pump to SHG
light.
The SHG spectrum gets boosted in magnitude near the phasematching point.
This effect will reveal the phasematching point ∆k = 0 when approached.
Figure 4.14: Mapping between SHG spectrum and pump spectrum as
predicted by theory
The setup for this experiment remained the same as the setup for the identification
of different SHG processes (see Figure 4.12). We monitored simultaneously the pump
and the SHG spectra, and choose type-II SHG generation. We pumped the crystal
with yz-polarized light and monitored the y-polarized SHG photons.
Different pump wavelengths between 1500 nm and 1600 nm were established. We
measured ’non-phasematched’ SHG as plotted in figure 4.15. In this Figure suitable
pump power creates only minimal SHG light. A great increase in SHG intensity
can be seen in Figure 4.16 around 780 nm. This reveals the phasematching point at
this wavelength. For this kind of measurement, it is necessary to guide enough laser
power inside the waveguide. Insufficient laser power will result in no detectable SHG
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