106
4 In the Field of Quantum Technologies
Fig. 4.3 Measurement data from VECSEL-chip Z-scan experiments revealing the wavelength- and
angle-dependent nonlinear absorption (a) and nonlinear refraction (b): Both nonlinear coefficients
are displayed for three incidence angles, that are 10, 20 and 30 ◦ with regard to the left axis in a, b as
a function of the wavelength. Arrows on top of the diagram indicate the PL from the quantum-well
(QW) gain medium and the different angle-dependent longitudinal-confinement factor (LCF) peaks.
Shaded plots show the corresponding angle-dependent surface PL from the chip for comparison.
Similarly, reflectivity spectra for the three angles are displayed as line plots. Both the PL and
reflectivity are normalised to 1 (right axes). Inset: sketch of the probe geometry with respect to the
VECSEL chip. Details and explanations about the experiment are provided in [101]. Reproduced
with permission. [101] Copyright 2019 Optical Society of America
light), nonresonantly-excited charge-carrier densities were introduced—in the relevant range for operation, below and above the laser’s threshold density. Thereby, an
angle-dependent, wavelength-dependent negative nonlinear refraction profile as well
as nonlinear absorption profile was revealed (Fig. 4.3) which is strongly shaped by
4 In the Field of Quantum Technologies
Fig. 4.3 Measurement data from VECSEL-chip Z-scan experiments revealing the wavelength- and
angle-dependent nonlinear absorption (a) and nonlinear refraction (b): Both nonlinear coefficients
are displayed for three incidence angles, that are 10, 20 and 30 ◦ with regard to the left axis in a, b as
a function of the wavelength. Arrows on top of the diagram indicate the PL from the quantum-well
(QW) gain medium and the different angle-dependent longitudinal-confinement factor (LCF) peaks.
Shaded plots show the corresponding angle-dependent surface PL from the chip for comparison.
Similarly, reflectivity spectra for the three angles are displayed as line plots. Both the PL and
reflectivity are normalised to 1 (right axes). Inset: sketch of the probe geometry with respect to the
VECSEL chip. Details and explanations about the experiment are provided in [101]. Reproduced
with permission. [101] Copyright 2019 Optical Society of America
light), nonresonantly-excited charge-carrier densities were introduced—in the relevant range for operation, below and above the laser’s threshold density. Thereby, an
angle-dependent, wavelength-dependent negative nonlinear refraction profile as well
as nonlinear absorption profile was revealed (Fig. 4.3) which is strongly shaped by