Intensity dependent self-action of a continuous wave (CW) or pulsed
optical beam can lead to spatial or spectral effects upon propagation
through a nonlinear medium, which can be described as an intensity
dependence of the refractive index, known as self-phase modulation
(SPM). In this work, we revisit the nonlinear optical propagation of a
CW and a CW mode-locked (CW-ML) high repetition rate [
∼
megahertz (MHz)] laser propagating
through pure ethanol in regions of very low optical absorption
(800 nm) or very high absorption (1480 nm, 1560 nm). Spatial and
spectral SPM and
Z
-scan experiments were performed to
clarify the origin of the third-order nonlinear optical response in
the different optical excitation regimes. From spatial SPM and
Z
-scan at either CW or CW-ML MHz
regime, a thermal nonlinear response was determined to be the origin
of the nonlinearity at 800 nm or 1480 nm, 1560 nm region, with the
nonlinear refractive index response of the order of
10
−
4
−
10
−
9
c
m
2
/
W
. From the spectral SPM, the
non-thermal origin of the nonlinearity, arising from electronic or
nuclear processes in the ethanol, was determined, and values of the
order of
10
−
13
−
10
−
16
c
m
2
/
W
were obtained, depending upon the
spectral region. The results were supported by theoretical
calculations using the nonlinear Schrödinger equation for the spectral
behavior or Fresnel–Kirchhoff integral for the spatial results and
clarify some of the misinterpreted results reported in the literature,
besides complementing other nonlinear refraction data available at
different wavelengths from 355 nm to 1560 nm.
We report experimental studies of spatial self-phase modulation (SSPM) in liquid suspensions of semiconducting MoS 2 , MoSe 2 , MoTe 2 , WS 2 , semimetallic ZrTe 2 , WTe 2 , and metallic NbS 2 , NbSe 2 using linearly and circularly polarized light with CW or CWmode-locked (ML) excitation lasers. For the semiconducting suspension of nanoflakes, excitation above and below the bandgap was performed. The results show that the intensity-dependent changes in the refractive index responsible for SSPM and associated ring formation are explained as arising from thermal origin. Measured values of the effective thermal nonlinear coefficient, n 2,th , range from ∼4.3 × 10 −7 to ∼4.2 × 10 −5 cm 2 /W, depending on the absorption strength of the suspension, and are independent of the optical excitation regime (polarization and laser mode of operation). The use of circularly polarized light to obtain the same results as seen with linearly polarized light is fundamental to complement the results, demonstrating that at the spectro-temporal regimes studied, thermal nonlinearity explains well the ring formation, in addition to providing the original SSPM results for NbS 2 , ZrTe 2 , and WTe 2 .
In its 60 years of existence, the field of nonlinear optics has gained momentum especially over the past two decades thanks to major breakthroughs in material science and technology. In this article, we present a new set of data tables listing nonlinear-optical properties for different material categories as reported in the literature since 2000. The papers included in the data tables are representative experimental works on bulk materials, solvents, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and materials suitable for nonlinear optics at THz frequencies. In addition to the data tables, we also provide best practices for performing and reporting nonlinear-optical experiments. These best practices underpin the selection process that was used for including papers in the tables. While the tables indeed show strong advancements in the field over the past two decades, we encourage the nonlinear-optics community to implement the identified best practices in future works. This will allow a more adequate comparison, interpretation and use of the published parameters, and as such further stimulate the overall progress in nonlinear-optical science and applications
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