4.2 Coherent Light Sources
105
Fig. 4.2 Experimental setup schematically displaying an ultrafast mode-locked VECSEL (a)
employed as a pump source for a single-photon source (b), from which a record-high single-photon
flux was obtained [34] (also see Fig. 4.7). a A z-shaped VECSEL resonator with semiconductor
saturable-absorber mirror (SESAM) delivers a 500-MHz pulse train of ps-pulses in the IR region,
which are frequency-doubled externally in a nonlinear crystal (BBO) to a wavelength of 508 nm.
These green laser pulses are directed to a typical micro-PL experiment (b) with a cryostat containing a quantum-dot–microlens (an AFM image of the produced 2 µm-diameter microlens device
is displayed in c and a Hanbury–Brown-and-Twiss (HBT) setup behind a double monochromator
for wavelength-sensitive second-order temporal autocorrelation function measurements. OC: Output coupler. MM: Multi-mode. MO: Microscope objective. TCSPC: Time-correlated single-photon
counting. Reproduced with permission. [34] Copyright 2015 AIP Publishing
wavelength) to the visible (see [99] for a red-emitting VECSEL exhibiting self-modelocking under stable single-pulse operation at a repetition rate of 3.5 GHz). Only due
to more advanced characterisation in support of a mode-locked operation claim,
this field could be established as a promising research direction (for an overview of
self-mode-locked VECSELs, see [100]).
Nonlinear Optics in the VECSEL Chip
To understand whether the mechanism behind pulse formation through self-modelocking is governed by a Kerr-lensing effect, as has been one major work hypothesis
in this field, or another effect or, likely, an interplay of different complementary
effects, preliminary studies aimed at the characterisation of the effective nonlinear
refractive index in “black-box” VECSEL chips [101–105].
Among these studies, the works by Kriso et al. not only investigated nonlinear
refraction, but also nonlinear absorption. More importantly, these optical nonlinearities were systematically studied as a function of the microcavity resonance, as
well as of the probe wavelength in the spectral vicinity of the laser’s output mode
[101], and as a function of the optical irradiance [105]. By optical irradiance (pump
105
Fig. 4.2 Experimental setup schematically displaying an ultrafast mode-locked VECSEL (a)
employed as a pump source for a single-photon source (b), from which a record-high single-photon
flux was obtained [34] (also see Fig. 4.7). a A z-shaped VECSEL resonator with semiconductor
saturable-absorber mirror (SESAM) delivers a 500-MHz pulse train of ps-pulses in the IR region,
which are frequency-doubled externally in a nonlinear crystal (BBO) to a wavelength of 508 nm.
These green laser pulses are directed to a typical micro-PL experiment (b) with a cryostat containing a quantum-dot–microlens (an AFM image of the produced 2 µm-diameter microlens device
is displayed in c and a Hanbury–Brown-and-Twiss (HBT) setup behind a double monochromator
for wavelength-sensitive second-order temporal autocorrelation function measurements. OC: Output coupler. MM: Multi-mode. MO: Microscope objective. TCSPC: Time-correlated single-photon
counting. Reproduced with permission. [34] Copyright 2015 AIP Publishing
wavelength) to the visible (see [99] for a red-emitting VECSEL exhibiting self-modelocking under stable single-pulse operation at a repetition rate of 3.5 GHz). Only due
to more advanced characterisation in support of a mode-locked operation claim,
this field could be established as a promising research direction (for an overview of
self-mode-locked VECSELs, see [100]).
Nonlinear Optics in the VECSEL Chip
To understand whether the mechanism behind pulse formation through self-modelocking is governed by a Kerr-lensing effect, as has been one major work hypothesis
in this field, or another effect or, likely, an interplay of different complementary
effects, preliminary studies aimed at the characterisation of the effective nonlinear
refractive index in “black-box” VECSEL chips [101–105].
Among these studies, the works by Kriso et al. not only investigated nonlinear
refraction, but also nonlinear absorption. More importantly, these optical nonlinearities were systematically studied as a function of the microcavity resonance, as
well as of the probe wavelength in the spectral vicinity of the laser’s output mode
[101], and as a function of the optical irradiance [105]. By optical irradiance (pump