Diploma thesis

Material: KTP
Polarizations: y → y + z
400 nm → 800 nm + 800 nm
Λ: 8.85 µm
m: 1
Pump FWHM: 1.5 nm
Dimensions: 4 µm x 4 µm x 3.5 mm
Table 3.3: Investigated crystal and pump parameters
We define the loss in brightness as
Iloss =
� ∞ � ∞
0
dωs dωi e −2 (ω i −ω f )2
2σ 2 f f(ωs, ωi) 2
�0 ∞ � ∞
dωs dωif(ωs, ωi) 2
0
0
(3.56)
and calculate for every filter width the corresponding cooperativity parameter in
addition to the intensity loss. Our results are plotted in Figure 3.36. This plot
characterizes the problem with the filtering approach. For a suitable amount of
decorrelation filters with a width below 1 nm have to be applied. The tradeoff
between decorrelation and intensity loss is huge, but can be compensated by a longer
measurement time.
1/K and Brightness
1
0.8
0.6
0.4
0.2
Filtering the JSA
0
0 2 4 6 8 10 12 14 16 18 20 22
Filter sigma [nm]
Brightness
1/K
Figure 3.36: Loss in brightness and gain in purity for different filter bandwidths
In this crystal higher order spatial modes lead to a minimal shift in the phasematching
function and the result is a vast array of JSAs that produce downconverted
28