The field of nonlinear optics (NLO) has been continuously growing over the past decades, and several NLO data tables were published before the turn of the century. After the year 2000, there have been major advances in materials science and technology beneficial for NLO research, but a data table providing an overview of the post-2000 developments in NLO has so far been lacking. Here, we introduce a new set of NLO data tables listing a representative collection of experimental works published since 2000 for bulk materials, solvents, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and THz NLO materials. In addition, we provide a list of best practices for characterizing NLO materials. The presented data tables and best practices form the foundation for a more adequate comparison, interpretation, and practical use of already published NLO parameters and those that will be published in the future.
The field of Nonlinear Optics (NLO), launched about 60 years ago, has gained considerable momentum over the past two decades, resulting in an enormous growth in NLO publications for a wide range of material categories, including bulk materials, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, and hybrid waveguiding systems. However, a convenient summary of NLO data collected since 2000 for these different material types has been lacking and would be a valuable resource for researchers in the field. Here, we present a new set of data tables showcasing a representative list of NLO properties taken from the literature since 2000 on the above-mentioned material categories. Furthermore, we provide best practices for performing and reporting NLO experiments. These best practices underpin the selection process that we used for including papers in the tables, and also form the foundation for a more adequate comparison, interpretation, and use of the NLO parameters published today and those that will be published in the future.
Since the first reports of their successful synthesis in 2015, all-inorganic perovskite quantum dots (PQDs), emerged as promising material for lighting applications. Despite their unique optical properties, to date, PQDs based LEDs and lasing media operation is still far from ideal. One of the limiting factors is the strong Coulomb interaction, which contributes to nonradiative decay processes. Here, we discuss in detail the multiexciton interactions in PQDs based on their size dependence. We expand on their nonlinear optical properties, focusing on the two-photon absorption characteristics, showing results for two-photon pumped amplified stimulated emission, suggesting that these materials may be promising for two-photon pumped lasers.
We report on transient absorption experiments performed at high optical excitation fluences and used to study the ultrafast dynamics in graphene. We employed a degenerated scheme of pump and probe at 800 nm (1.55 eV). The time resolution of our measurements was limited by the pulse duration ~ 100 fs. The samples were prepared by chemical vapor deposition (CVD) as single-layers on silica and, then staked layer-by-layer in order to make a stack of up to 5 graphene monolayers. We observed saturable absorption (SA) and fluence-dependent relaxation times. We see that the ultrafast carrier dynamics is composed by two decay mechanisms, one with response time of about 200 fs and a slower process of about 1 ps. The fast decay, due to both carrier-carrier and carrier-optical phonon scattering, becomes slower when the density of excited carrier was increased. We implemented a theoretical model and found that both the optical phonon rate emission and the optical phonon lifetime are affect by the pump fluence.
Energy-resolving gamma-ray detectors are of particular interest for the detection of illicit radioactive materials at border crossings and other portals because they offer fast, contactless screening that can discriminate between dangerous and benign materials. Among detector classes, scintillators offer an intriguing balance between cost and performance, but current technologies rely on single-crystal materials that are not scalable to portal-relevant detector sizes. Thus, there is a recognized need for novel, processible, high-performance scintillating materials or composites. Composites based on semiconductor nanocrystal quantum dots (QDs) are of interest because of their potentially high gamma-stopping power, high emission quantum yields, and low-cost solution synthesis and processing. Yet the performance of these and other granular nanomaterials has not met expectations. We suggest that this is due to the general lack of insight into the gamma-to-photons transduction process within these inherently more complex materials, which reduces the development and refinement of candidates to simple trial-and-error. Here, we describe the development of ultrafast transient cathodoluminescence as a unique spectroscopic tool for probing the population of excited states formed within a material during scintillation, and thus determining the major sources of energy loss. Our analysis shows that in the case of CdSe/ZnS core/shell QDs, any efficiency loss due to previously blamed factors of low-stopping power and high reabsorptive losses are likely dwarfed by the losses attributable to efficient, non-radiative Auger recombination. We examine how we reached this conclusion, and how this insight defines the characteristics needed in the next generation of scintillating QD composites.
Understanding the nonlinear optical processes in semiconductor nanostructures leads to possible applications in areas
including laser amplifiers, optical switches, and solar cells. Here we present a study of the frequency degenerate two-photon
absorption (2PA) spectrum of a series of PbS and PbSe quantum dots (QDs). The influence of the quantum
confinement is analyzed using a four-band model which considers the mixing of valence and conduction bands. In
contrast to our observations of CdSe QDs, the present results point to an increase of the 2PA cross-section (normalized
by the QD volume) as the quantum dot size is made smaller. This is explained by the symmetry between the valence and
conduction bands which allows the density of states to remain high even for small QDs. A study of the ultrafast carrier
dynamics of the PbS quantum dots is also presented. Through nondegenerate femtosecond pump-probe experiments we
show evidence of multi-exciton generation with quantum yield (number of excitons generated per absorbed photon) up
to 170% for excitation with hω> 3 Eg (where Eg is the bandgap energy).
We have been developing tools for nonlinear spectroscopy aimed toward the ultimate goal of building a nonlinear
spectrophotometer analogous to the ubiquitous linear spectrophotometer where a sample is placed in the instrument, a
button is pushed, and the absorption spectrum is obtained sometime later. This paper describes our progress toward this
goal, describing many difficulties and complications as well as opportunities. We also show spectroscopic data and
analysis of a variety of materials that we have taken with preliminary nonlinear spectroscopic instrumentation we have
already developed. One of the more interesting observations obtained along this research path is the realization that
linear dispersion theory can also be applied to nonlinear systems when formulated properly such that Kramers-Kronig
relations can be used to connect the dispersion of nonlinear refraction to the spectrum of nonlinear absorption. In some
circumstances this can be more easily applied to nonlinear systems than to linear systems since the nonlinear absorption
spectrum can be limited in wavelength. In addition, we have developed tools that can simultaneously give the spectrum
of nonlinear absorption as well as the dispersion of the nonlinear refraction over an octave spectral range from 400nnm
to 800 nm, the so called White-Light-Continuum Z-scan. Much of the research on nonlinear optical materials has been a
collaborative effort requiring the skills and expertise of organic chemists and materials manufacturers. The goals of this
part of the research are to determine predictive structure-property relation capabilities. The database needed for this
research makes the nonlinear spectrophotometer a necessity.
We present the design, fabrication and characterization of the optical properties of one-dimensional metal-organic
photonic bandgaps (MO-PBGs) composed of a tetraphenyldiaminobiphenyl-based polymer and ultrathin electrically
continuous Cu layers. The fabricated MO-PBGs achieve a peak transmission of around 44% at 620 nm combined with
very large spectral, around 120 nm FWHM, and angular, more than 120° field-of-view, bandwidths. Using 140 fs pulses
at various wavelengths we have found up to 10 × enhancements in the nonlinear optical (NLO) properties of the MO-PBGs
when compared with the NLO response of ultrathin electrically continuous Cu layers.
We present degenerate and nondegenerate two-photon absorption spectra in a series of CdSe and CdTe quantum dots. The measurements show that the two-photon absorption (2PA) spectrum is strongly dependent on the quantum dot size and that the 2PA coefficient decreases as the quantum dot size decreases, and it is larger for the frequency nondegenerate process. Previously we had shown a theoretical analysis of these results based on a simple model using the effective mass approximation. Although this model works well for larger quantum dots, it fails for the smaller ones. Here we use the more (formula available in manuscript) model for the band structure and consider the hole band mixing in quantum dots to describe our data. This theory better describes the spectral structures for smaller quantum dots and also predicts the decrease of the 2PA coefficient with the decrease of quantum dot size. This is due to the reduction of the number of possible transitions and the blue shift of the optical bandgap from quantum confinement. This theory predicts the reduction of the 2PA coefficient with size, although our experimental results show an even stronger reduction.
The nonlinear optical performance of several Fluorene-based molecules was studied using different measurement methods and pulse durations. We used picosecond pulses at 532 nm and, femtosecond pulses tunable from 532-810 nm for performing open and closed aperture Z-scans, and we used femtosecond 570-930 nm pulses for two-photon induced fluorescence (2PF) spectroscopy. The observed nonlinear losses were compared using the three methods. The results exhibit much stronger nonlinear absorption with picosecond pulses due to the additional excited-state absorption processes involved. Also the nonlinear refractive index was found to be higher for the picosecond measurements. In addition using a femtosecond white-light continuum (WLC) pump-probe method we showed that by proper tuning of pump and probe wavelengths an intermediate state resonance enhancement (ISRE) of the 2PA can be observed yielding the same overall nonlinear absorption observed using picosecond pulses.
Both degenerate and nondegenerate two-photon absorption (2PA) spectra are studied in two different samples of CdTe quantum-dots in borosilicate glass hosts. One sample (CdTe-600) contains quantum-dots of radius 3.2 ± 0.2 nm and has its absorption edge at 600nm. The other sample (CdTe-750) contains quantum-dots of radius 6.6 ± 0.9 nm and absorption edge at 750nm. CdTe-600 contains quantum-dots with a narrower size distribution than CdTe-750. Consequently, the peaks corresponding to discrete transitions are more clearly visible in CdTe-600 than in CdTe-750. Both nondegenerate and degenerate spectra for these samples show a marked difference from bulk CdTe. In CdTe-750 the two-photon absorption spectrum has a shape similar to that for bulk solids but for CdTe-600 the 2PA spectrum is somewhat different from that expected for the bulk. In the Z-scan measurements we also observed a photo-darkening effect, which is accompanied by an increase in the measured effective 2PA coefficient. All results suggest that 2PA cannot be predicted by the bulk theory especially near to the 2PA edge, that the 2PA in quantum dots is generally smaller than would be expected for the same volume of bulk semiconductor with the same band edge, and that the quantum-dot size and size distribution play important roles in the 2PA spectral behavior and magnitude.
Thin films of glass doped with PbTe quantum dots were successfully fabricated. The semiconducting quantum dots were grown by laser ablation of a PbTe target (99.99%) using the second harmonic of a Q-Switched Quantel Nd:YAG laser under high purity argon atmosphere. The glass matrix was fabricated by a plasma chemical vapor deposition method using vapor of tetramethoxysilane (TMOS) as precursor. The QD's and the glass matrix were alternately deposited onto a Si (100) wafer for 60 cycles. Cross-section TEM image clearly showed QD's layer well separated from each other with glass matrix layers. The influence of the ablation time on the size distribution of the quantum dots is studied. HRTEM revealed anisotropy in the size of the QD's: they were about 9nm in the high and 3-5 in diameter. Furthermore HRTEM studies revealed that the QD's basically growth in the (200) and (220) directions. The thickness of the glass matrix layer was about 20 nm. Absorption, photo luminescence and relaxation time of the multilayer were also measured.
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