Natalia Munera

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.

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.

The implementation of a digital holographic interferometry setup for high-speed micro-deformation measurement is presented. This proposal uses a dual-wavelength recording strategy to reconstruct micro-deformations up to 4.85 µm with no phase wrapping. The numerical processing required to recover the phase maps containing the information of micro-deformations is carried out in a general-purpose computing on graphics processing unit environment to boost its performance. The method completely processes recorded holograms of 1024 × 1024 p i x e l s in 48 ms, i.e., 21 frames per second (FPS) for a single-wavelength acquisition and 96 ms or 11 FPS for dual-wavelength recordings. The method is experimentally evaluated measuring deformations ranging from 0.033 µm to 4.85 µm with no need for phase unwrapping algorithms for an 8 cm diameter aluminum plate in a 110 c m 2 field of view.

We use the polarization-sensitive, time-resolved Beam-Deflection technique to measure the nonlinear refraction of air, exciting in both the near and mid-IR and probing in the mid-IR. This gives us the first measurements for air using both excitation and probe in the mid-IR, and we find no dispersion of the bound-electronic nonlinear refractive index, n_2,el(λ _p ;λ _e ), assuming, as has been shown earlier, that the nuclear rotational nonlinear refraction is nearly dispersionless. From these data, we can model the pulsewidth dependence of the effective nonlinear refractive index, n_2,eff, i.e., as would be measured by a single beam. Interestingly, n_2,eff is maximized for a pulsewidth of approximately 0.5 ps. The position of this maximum is nearly independent of pressure while its magnitude decreases with increasing pressure and temperature. From the measurements and modeling, we predict the nonlinear refraction in the atmosphere at different altitudes.

The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as non-fullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 10³ GM) in the near infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (7 rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement and their moderate magnitudes (ca. 10^-21 m²) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.

We used the polarization-resolved beam-deflection technique to separate the bound-electronic and molecular-rotational components of the transient nonlinear refraction (NLR) of ambient air in the Mid-infrared spectral range below the ionization threshold.

We present a detailed study of the nonlinear pulse propagation in a commercial hollow-core photonic crystal fiber (PCF), whose core was infiltrated with carbon disulfide (CS 2 ), an organic solvent with high nonlinear properties useful to increase the performance of the supercontinuum generation (SCG) in terms of the bandwidth centered at the telecom range. We included the recently CS 2 response function measured by Reichert et al [1] which gives rise to a new so-called hybrid soliton due to the slow response of the material [2]. We also study the dependence of SCG on several input parameters such as pulse width, energy, and length of the liquid-core PCF (LCPCF). The zero dispersion wavelength was numerically found around 1.86 μm for this geometry. In this sense, the pump wavelength was chosen to be around 1.95 μm in order to ensure propagation in the anomalous dispersion regime.

The third-order optical nonlinearities of Si and GaAs have been characterized throughout the near-infrared spectral region (1.1-2 μm) using multiple ultrafast spectroscopic techniques. These results have been independently confirmed at two different laboratories.