Eric W. Van Stryland

A prescription for determining the nondegenerate three-photon absorption spectrum of zinc-blende semiconductors is presented. Theoretical calculations based on third-order perturbation theory and Kane’s band structure provide the nondegenerate three-photon absorption coefficient for any combination of photon energies and polarizations. The enhancement over three orders of magnitude is predicted when using extremely nondegenerate photon energies, which is greater than that predicted with two-photon absorption. A large polarization dependence is predicted for excite-probe measurements (two photons absorbed from the excitation and one from the probe), with variation between parallel and perpendicular polarizations of up to a factor of 10 with a significant spectral dependence. Experimental measurements on zinc-blende GaAs and ZnSe show excellent agreement with the predicted spectral shape, nondegenerate enhancement, and polarization dependence. In addition, wurtzite CdS also shows a large enhancement over the degenerate case.

There is growing interest in the refractive index of liquids beyond the visible and into the short-wave infrared (SWIR) for applications such as the study of liquid-core fibers and supercontinuum generation. However, most of the data reported are in the visible. For liquids with a wide transmission window in the SWIR region, refractive index data are sparse. We present a Rayleigh interferometry-based refractometer to characterize the refractive index relative to standard materials at seven different wavelengths (543.4, 632.8, 780, 973, 1064, 1550, and 1970 nm) at a temperature of ~ 21.3 ± 0.6 °C. We also show Sellmeier fits using our results juxtaposed with previously published data. Our data extends previous work to the SWIR.

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.

Epsilon-near-zero (ENZ) materials have emerged as viable platforms for strong nonlinear optical (NLO) interactions. The NLO phase shift in materials exhibiting an ENZ condition is extremely large; however, direct experimental measurements of the magnitude and time dynamics of this phenomenon, particularly nondegenerate NLO phase shifts, have so far been lacking. Here, we directly measure the NLO phase shift of an Indium-Tin-Oxide (ITO) thin film using three different techniques. By characterizing the excitation-induced, time-resolved beam deflection (BD) of a probe beam, we measure the nondegenerate NLO effects, allowing a separate determination of the effects of excitation and probe wavelengths on the NLO phase shift as they are varied across the ENZ region. These experiments reveal that having the probe pulse centered at ENZ greatly contributes to this enhancement; however, the NLO phase shift is less sensitive to the excitation wavelength, which only slightly enhances the nonlinearity for obliquely incident TM-polarized light. We also find that the spectral shift of the probe pulse induced by the excitation follows both the magnitude and time dynamics of the NLO phase shift measured via the BD experiments. We observe large, ultrafast cross-phase modulation in agreement with a redistribution of carriers in the conduction band. Finally, using the Z-scan method, we measure the degenerate nonlinear refraction at ENZ near normal incidence. The results of all three measurements agree, revealing a gigantic sub-picosecond NLO phase shift in ITO. At its largest, we consistently measure an effective induced index change greater than the linear index.

Epsilon-near-zero (ENZ) materials have emerged as viable platforms for strong nonlinear optical (NLO) interactions. The NLO phase shift in materials exhibiting an ENZ condition is extremely large, however, direct experimental measurements of the magnitude and time dynamics of this phenomenon, particularly nondegenerate NLO phase shifts, have so far been lacking. Here, we directly measure the NLO phase shift of an Indium-Tin-Oxide (ITO) thin film using three different techniques. By characterizing the excitation-induced, time resolved Beam Deflection (BD) of a probe beam, we measure the nondegenerate NLO effects, allowing a separate determination of the effects of excitation and probe wavelengths on the NLO phase shift as they are varied across the ENZ region. These experiments reveal that having the probe pulse centered at ENZ greatly contributes to this enhancement; however, the NLO phase shift is less sensitive to the excitation wavelength, which only slightly enhances the nonlinearity for obliquely incident TM-polarized light. We also find that the spectral shift of the probe pulse induced by the excitation follows both the magnitude and time dynamics of the NLO phase shift measured via the BD experiments. We observe large, ultrafast cross-phase modulation in agreement with a redistribution of carriers in the conduction band. Finally using the Z-Scan method, we measure the degenerate nonlinear refraction at ENZ near normal incidence. The results of all three measurements agree, revealing a gigantic sub-picosecond NLO phase shift in ITO. At its largest, we consistently measure an effective induced index change that is greater than the linear index.

The fast relaxation processes in the excited electronic states of functionalized aza‐boron‐dipyrromethene (aza‐BODIPY) derivatives (1–4) were investigated in liquid media at room temperature, including the linear photophysical, photochemical, and nonlinear optical (NLO) properties. Optical gain was revealed for nonfluorescent derivatives 3 and 4 in the near infrared (NIR) spectral range under femtosecond excitation. The values of two‐photon absorption (2PA) and excited‐state absorption (ESA) cross‐sections were obtained for 1–4 in dichloromethane using femtosecond Z‐scans, and the role of bromine substituents in the molecular structures of 2 and 4 is discussed. The nature of the excited states involved in electronic transitions of these dyes was investigated using quantum‐chemical TD‐DFT calculations, and the obtained spectral parameters are in reasonable agreement with the experimental data. Significant 2PA (maxima cross‐sections ∼2000 GM), and large ESA cross‐sections ∼10⁻²⁰ m² of these new aza‐BODIPY derivatives 1–4 along with their measured high photostability reveal their potential for photonic applications in general and optical limiting in particular.

Pd(PPh ₃ ) ₂ Cl groups hinder aggregation and afford promising solid-state NLO properties.

Weakly focused, near mJ, 1800nm femtosecond pulses in a 1.8m Krypton gas chamber generates a high-spectral-irradiance, Gaussian spatial profile continuum for nonlinear spectroscopy in the 800-1600nm range. We demonstrate its usefulness with Z-scans on GaAs.

The dispersion of nondegenerate nonlinear refraction in semiconductors is measured using our beam-deflection method. With high nondegeneracy, n₂ is significantly enhanced over degenerate case, and rapidly switches sign to negative near the bandgap.

Nonlinear absorption refers to any effect in which a material's optical transparency depends on the intensity of the illumination. This includes changes in which the transparency increases or decreases. Such processes can occur almost instantaneously as in two-photon absorption, or can accumulate in time as in optically triggered chemical reactions (e.g., the mechanism in many photochromic sunglasses). In general, the magnitude of the nonlinear optical response gets smaller as the response time gets faster. Thus, slow nonlinear optical effects can be observed with sunlight while fast effects require pulsed laser beams. This entry discusses many but by no means all such effects. In general, nonlinear refraction accompanies nonlinear absorption since these processes are intimately connected by causality. Thus, this entry is a companion to the one on nonlinear refraction by M. Sheik-Bahae and M. Hasselbeck. In that entry, the causal relationship is described in more detail.