164
5 Optical Measurement Techniques
Fig. 5.14 a Typical Z-scan setup based on a mode-locked Ti:sapphire laser system and two intensity
detectors (power meter heads) analysing the reflected beam from a translated sample. Here, the
experiment is set up in reflection geometry to meet the requirements of VECSEL chip investigations
[108]. Two lock-ins are used for signal acquisition in combination with a chopper wheel. The
irradiation is adjusted by neutral-density (ND) filters. b Z-scan measurement at a fixed probe
wavelength for different irradiances, measured for an incidence angle of 20 ◦ . The corresponding
open scan c recorded by detector 1 shows nonlinear absorption. A partially closed aperture in front
of detector 2 is used to obtain nonlinear lensing signatures in the trace. To obtain the Z-scan trace,
the closed scan is corrected for nonlinear absorption by dividing it by the open scan, a background
subtraction with a low-intensity scan is performed and the transmission at z positions far away
from the focus region is normalised to a transmittance of 1. Reproduced with permission. [108]
Copyright 2019 Optical Society of America
recently investigated with regard to their nonlinear refraction and absorption using
the Z-scan method [110].
5.4.2 Nonlinear Frequency Conversion
Nonlinear processes can enrich the study of materials and structures. Among these
processes are particularly famous SHG [124] and difference-frequency generation
(DFG). In addition, the Kerr effect and other nonlinear processes such as optical
rectification can be used to generate strong fields of electro-magnetic radiation (cf.
[125, 126]) or white-light supercontinuum spectra (e.g., in fibers, see for instance
[127]) which are both desired for different spectroscopic applications.
On the one hand, higher-harmonic generation such as SHG and third-harmonic
generation (THG) can be used to probe crystal symmetries of a given sample due to
the dependence of nonlinear frequency conversion efficiencies on the tensor-elements
5 Optical Measurement Techniques
Fig. 5.14 a Typical Z-scan setup based on a mode-locked Ti:sapphire laser system and two intensity
detectors (power meter heads) analysing the reflected beam from a translated sample. Here, the
experiment is set up in reflection geometry to meet the requirements of VECSEL chip investigations
[108]. Two lock-ins are used for signal acquisition in combination with a chopper wheel. The
irradiation is adjusted by neutral-density (ND) filters. b Z-scan measurement at a fixed probe
wavelength for different irradiances, measured for an incidence angle of 20 ◦ . The corresponding
open scan c recorded by detector 1 shows nonlinear absorption. A partially closed aperture in front
of detector 2 is used to obtain nonlinear lensing signatures in the trace. To obtain the Z-scan trace,
the closed scan is corrected for nonlinear absorption by dividing it by the open scan, a background
subtraction with a low-intensity scan is performed and the transmission at z positions far away
from the focus region is normalised to a transmittance of 1. Reproduced with permission. [108]
Copyright 2019 Optical Society of America
recently investigated with regard to their nonlinear refraction and absorption using
the Z-scan method [110].
5.4.2 Nonlinear Frequency Conversion
Nonlinear processes can enrich the study of materials and structures. Among these
processes are particularly famous SHG [124] and difference-frequency generation
(DFG). In addition, the Kerr effect and other nonlinear processes such as optical
rectification can be used to generate strong fields of electro-magnetic radiation (cf.
[125, 126]) or white-light supercontinuum spectra (e.g., in fibers, see for instance
[127]) which are both desired for different spectroscopic applications.
On the one hand, higher-harmonic generation such as SHG and third-harmonic
generation (THG) can be used to probe crystal symmetries of a given sample due to
the dependence of nonlinear frequency conversion efficiencies on the tensor-elements