This PDF file contains the front matter associated with SPIE Proceedings Volume 11497, including the Title Page, Copyright Information, and Table of Contents.

Time-resolved magneto-optical Kerr microscopy measures the spatio-temporal evolution of electron spin textures in modulation-doped GaAs and CdTe quantum wells. The structures feature similar Dresselhaus and Rashba coefficients, such that there is negligible impact of spin-orbit coupling for electrons moving along the [11̅0] or [1̅10] directions. In contrast, strong spin-orbit coupling emerges for electrons moving perpendicular to those crystallographic directions. As a result, we observe a helical spin pattern often refered to as persistent spin helix. After analyzing the purely diffusive electron motion after ultrafast optical spin injection we move on to study the impact of in-plane electric fields, magnetic fields and the combination of both.

Most electrochemical processes occur in the electrode-solution interface, thus, understanding the structure and dynamic of the electric double layer is mandatory for the development of the field and its related technologies. Herein, we present an apparatus for in situ ultrafast dynamics and low-frequency stimulated Raman spectroscopy measurements of the electrochemical interface by time-resolved optical Kerr effect spectroscopy. We give details of the laser system, the spectroelectrochemcial cell, and calibration of the integrated setup. We studied the time-resolved measurements as a function of the sample position and the electrochemical potential. Analysis in the time and frequency domain together with root-mean-squared amplitude analysis of the nonlinear signals are shown. The results obtained by femtosecond spectroscopy depends on the electrochemical potential and are discussed in terms of orientation and collective molecular dynamics.

Femtosecond mode-locked lasers are an important tool for the physical and life sciences. However, applications such as biomedical imaging require complex and expensive auxiliary systems to achieve desirable wavelengths and pulse repetition rates. In this talk I will discuss progress on the development of a complementary approach to femtosecond pulse generation based on fiber Kerr resonators. Recent experimental and theoretical results reveal a range of new phenomena including the shortest pulses observed to date from a fiber Kerr resonator

Using two multiple-cycle optical pulses with incommensurate frequencies (e.g., at wavelengths 1400 nm and 800 nm) in a collinear configuration, a cascaded background-free four-wave mixing EUV field can be realized because the EUV pulse produced by phase-matched high order harmonic generation in combination with the other two optical pulses creates a third-order nonlinear polarisation which drives a phase-matched four-wave mixing process along the propagating direction. The four-wave mixing emission can be manipulated by varying the delay of the second optical pulse. The phase-matching of the four-wave mixing process together with the relatively long interaction path combine to produce a strong output signal which leads to an enhanced signal-noise ratio of the Fourier-transformed signal used to obtain the two-dimensional cross correlation spectrum. Some key features of this two-dimensional spectroscopy, such as the on-axis and off-axis peaks, can lead to the determination of interaction pathways of real dipole-allowed transitions and virtual transitions in the EUV.

The conversion of light into chemical and mechanical energy can take place at the level of single molecules, where the absorption of a photon leads to changes in the molecular structure on ultrafast time scales. Observing these dynamics requires simultaneously reaching atomic (sub-Angstrom) spatial resolution and femtosecond temporal resolution. We have recently showed that we can reach these milestones with ultrafast electron diffraction (UED), capturing structural dynamics in isolated molecules as they take place. We have observed bond breaking, the motion and splitting of nuclear wavepackets in complex photochemical reactions and coherent motions that persist after the reaction is completed.

The discovery of Archimedean spiral vortex patterns in single ionization of the helium atom by a pair of time-delayed, counter-rotating circularly-polarized attosecond pulses has created a new subfield in atomic molecular and optical (AMO) physics field. While this novel electron phenomenon has been demonstrated experimentally using femtosecond pulses and small binding energy atomic targets, our prediction of electron vortices has stimulated a number of theoretical studies for the occurrence of electron vortices in other atomic or molecular systems and linear or nonlinear processes. Great applications of electron vortices include laser pulse diagnostics, control of electron motions, control of charge migration in matter, imaging electron correlation processes while they occur, measuring of quantum mechanical phase of ionic states.

Ultrafast electron diffraction (UED) has become a leading technique for investigation of structural dynamics in solids providing high spatial and temporal resolutions. Radio frequency (RF) based photoinjectors providing Mega-electron-volt (MeV) scale electron beams are improving the source brightness and instrument versatility and are largely responsible for advancement of the field of structural dynamics. At Lawrence Berkeley National Laboratory (LBNL), an RF photoinjector gun for ultrafast structural studies using UED has been in development and is now producing high-quality scientific results. Here we describe some factors that enable UED of materials at LBNL and present some exemplary results.

Combining the temporal resolution of optical spectroscopy with the spatial resolution of electron microscopy, ultrafast transmission electron microscopy (UTEM) enables resolving out-of-equilibrium processes in heterogeneous systems on the sub-nanometer length scale using imaging, diffraction and spectroscopy ^[1]. Here, we employ the Göttingen UTEM ^[2] to unravel real-space dynamics of an order parameter to a charge-density wave (CDW) phase transition in the correlated material 1T-TaS2. Specifically, a tailored dark-field approach enables tracking of dynamics of the CDW amplitude with nanometer spatial resolution. Following a global CDW quench, we observe localized formation, condensation and subsequent spatiotemporal evolution of domain patterns on femtosecond to nanosecond time scales. We corroborate our findings by time-dependent Ginzburg-Landau simulations. ^[1] A. H. Zewail, Science 328, 187 (2010). ^[2] A. Feist et al., Ultramicroscopy 176, 63 (2017).

Ultrashort pulse characterization and measurement is critical in the field of ultrafast and nonlinear optics. Here we present a method to reconstruct the complex pulse profile using a colinear frequency resolved optical gating (CFROG) acquisition combined with a convolutional neural network (CNN). The CFROG approach can be implemented with nonlinear nanoprobes for probing complex ultrafast optical fields. Typically, a CFROG trace is filtered and converted to a standard FROG trace which can then be processed by using the FROG retrieval algorithm to reconstruct both the amplitude and the phase profiles of the pulse. In this method, however, the reconstruction is often dependent on the subjective filtering step. In our approach, a CNN is trained with simulated unfiltered CFROG traces. Furthermore, we customize the CNN architecture to mitigate the ambiguity in the solution space and minimizes the error between the predicted and the input

dWe demonstrate a nonlinear chiral meta-mirror consisting of an array of amorphous silicon split-ring resonators on top of a silver backplane with a silica spacer layer. This hybrid dielectric-plasmonic system can enhance Mie-resonance to result in strong light-matter interaction on the nanometer scale. The chiral meta-mirror exhibits a sharp absorption on one handedness of the circular polarization, and reflects the opposite handedness in a manner that preserves its polarization state in the linear regime. We show that the chiroptical responses can be tuned dynamically by leveraging photoexcited carriers in amorphous silicon. All optical, picosecond scale intensity modulation and polarization switching are studied.

The investigated functional materials make it possible to visualize, register, and digitize the volumetric picture of highly nonlinear interaction of light and matter. Using highly nonlinear photographs, including luminescent microtomograms, it is possible to reconstruct the configuration of intense light fields in self-action modes. Crystals with a wide band gap, in which the exciton mechanism of radiation-induced defect formation is realized, are investigated. The generated radiation defects are capable of photoluminescence, they are thermally and optically stable. These media are excellent materials for the manufacture of optical storage media in the form of images and in digital codes.

Chemical imaging of living cells is critically important for understanding the function and pathophysiology of biological systems such as the brain. The main obstacles are the limited amount of analyte in a single cell and the need for noninvasive in situ analysis in order to preserve cell function and microenvironmental information. We apply label-free chemical imaging methods to quantify the spatiotemporal distribution of important biomolecules at subcellular resolution. In combination with deep learning algorithms, we aim to build an integrated chemical imaging platform to study a wide range of normal and diseases processes in the brain.

Brain is a complex organ displaying cellular structural and functional heterogeneity. Understanding the dynamics of metabolism in brain with cellular resolution is essential to unraveling the mechanistic basis of many neuronal activities. Traditional imaging methods cannot provide metabolic activity information with high resolution in situ. We developed a new method that combines bioorthogonal labeling and Raman Scattering microscopy to visualize metabolic dynamics in brains. For example, the incorporation of deuterated glucose, or heavy water (D2O) into biomolecules will generate new carbon-deuterium (C-D) bonds in protein, lipids and nucleic acids in brain. We obtained new insights through high resolution imaging of whole brain, such as new protein and lipids synthesis in different brain regions during the developmental and aging processes. We demonstrate that this is an efficient methods for visualizing metabolic activities in brain.

We investigated the donor effects (mCerulean3 versus mTurquoise2.1) on the spectroscopy and dynamics of mCerulean3-linker-mCitrine constructs using integrated fluorescence spectroscopy methods. Here, mCerulean3 (a cyan fluorescent protein) and mCitrine (a yellow fluorescent protein) act as Förster resonance energy transfer (FRET) pair, separated by flexible linker region. We hypothesize that the construct with mTurquoise2.1 would have many advantages as a donor, which include a higher FRET efficiency as compared with the mCerulean3 due to the enhanced spectral overlap with mCitrine. To test this hypothesis, we used steady-state spectroscopy, time-resolved fluorescence, and fluorescence correlation spectroscopy of both mCerulean3-linker-mCitrine and mTurquoise2.1-linker-mCitrine to investigate the donor effect on the FRET efficiency and translational diffusion as a means for developing a rational design for hetero-FRET constructs for environmental sensing.

In this work, based on fluorescence blinking and blench microscope systems, we proposed a super-resolution method based on auto-correlation two-step deconvolution (SACD) to enhance the temporal resolution at lower signal intensity levels, utilizing LR deconvolution as two separated steps and combining with the multi-plan auto-correlation (MPAC). In this SACD model, the time-varying fluorescence intensity images can be analyzed and produce super-resolution images under insufficient frames involved or the sparse photons level. By using three typical datasets, i.e., the simulated fluctuation data, the experimental fluctuation data, and high density SMLM data, we demonstrate the accuracy and the effectiveness of our proposed SACD model. Our SACD and conventional methods are also compared in details and the reconstructions substantially outperform these current algorithms.

Upconversion nanoparticles (UCNP) is a lanthanide ion-doped nanocrystal that has a natural nonlinear photo-response from their upconverting energy transfer process. The nonlinearity can be further modified by changing the doping element and concentration. Here we present a strategy that applies UCNPs as near-infrared (NIR) nonlinear fluorescence probe for in-depth super-resolution imaging. We present a method that takes advantage of “non-diffractive” Bessel beam, further employs the photon-saturation of the NIR emission from UCNPs, so that enabling super-resolution mapping of single nanoparticles located 55 μm inside a spheroid, with a resolution of 98 nm, without adaptive optics compensation. We further apply the photon-conversion of UCNPs for a high efficient NIR nonlinear structured illumination microscopy (NIRNSIM) for a rapid in-depth super-resolution imaging. With 10 kW/cm2 continuous wave (CW) excitation, NIR-NSIM achieves a resolution of 130 nm, 1/7th of the excitation wavelength, and a frame rate of 1 fps, through 50 μm biological tissues.

In classical Two photon microscopy (TPM), fluorescence excitation happens via absorption of two photons with the same energy. However, the energies of the two photons do not need to be the same: the sum of their energies must be equal to the total energy required for the ground state to excited state transition. This feature allows for non-degenerate two-photon excitation (ND-TPE), where excitation occurs via simultaneous absorption of two photons of different energies derived from two laser beams. ND-TPE has been exploited in fluorescence microscopy to extend the range of excitation wavelengths , increase resolution, increase penetration depth, and mitigate excitation outside of the focal volume.We use non-degenerate two-photon excitation where the two excitation beams are displaced in space outside the focal volume to increase the signal-to-background ratio (SBR), overcoming the fundamental penetration depth limit of conventional two-photon microscopy.

Mid-infrared photothermal imaging is a novel chemical imaging modality that combines high sensitivity with enhanced spatial resolution. Subcellular features in fibroblast cells and tissues are imaged and analyzed with regards to their molecular structures without the need of exogenous fluorophores at a resolution that overcomes the diffraction limited spot size of the mid-infrared excitation beam. With a phase-sensitive lock-in detection scheme, changes in the thermal diffusion properties can be detected and can provide a complementary sample characterization.

Raman microscopy has been widely developed for label free nonlinear optical microscopy of biological systems. Imaging speed in these systems is hampered by low Raman scattering cross sections and the requirement of scanning a focused laser beam through the sample in conventional Raman microscopy. The serial acquisition that is necessary in point scanning microscopy slows image acquisition and limits the dwell time are each image pixel. Here, we discuss two new imaging methods that are based on spatial frequency modulation imagining (SPIFI) [1-2], where a structured line focus is used to image is used to image specimens by collecting light on a single pixel detector. We discuss the use of SPIFI to improve the imaging speed of Spontaneous Raman scattering and coherent anti-Stokes Raman scattering microscopy. A detailed noise analysis highlighting the advantages and disadvantages of SPIFI as compared to conventional point scan imaging is presented.

A novel polarization-modulation transient method has been developed for studying fast anisotropic relaxation in electronic excited states of polyatomic and biologically relevant molecules under excitation with femtosecond laser pulses. The method is based on the modulation of pump beam polarization with a photo-elastic modulator and detection of an anisotropic contribution to the transient signal by a highly-sensitive demodulation balanced scheme. The method was tested on aqueous solution of coenzyme NADH (nicotinamide-adenine-dinucleotide) pumped at 360 nm and probed at 720 nm. Anisotropic vibrational relaxation and rotational diffusion have been observed in the sub-picosecond time domain. The method significantly enhances the accuracy of transient measurements and allows for recording of high-quality signals at low energy (a nJ) pump pulses.

Fluorescence kinetics of the biological cofactor flavin adenine dinucleotide (FAD) in water-methanol solutions at 0%, 20%, 40%, 60% and 80% methanol concentration have been investigated. Fluorescence lifetimes, corresponding weighting coefficients, anisotropy, and rotational diffusion time were determined from experiment through analysis of the polarized fluorescence decay excited by picosecond laser pulses. The dependence of the fluorescence parameters on solution polarity and viscosity has been analyzed.

Lubricating oils are essential in vehicles motors, and there are currently three variations in oil types: mineral, semisynthetic and synthetic. This work aimed to evaluate the degradation of these three types, by heating them in the laboratory between 120 to 150 ºC for 48h, and subsequently evaluating their change in the composition through Raman spectroscopy. It was possible to observe compounds in common between the mineral and semi-synthetic oils in the peaks at 1002, 1380 and 1621 cm^-1, and between the semi-synthetic and synthetic in the peak at 892 cm^-1. In the evaluation of samples after heating, trough principal component analysis (PCA) technique, it was observed a decrease in the intensity of some peaks, suggesting molecular breakdown, as well as an increase in the intensity of other peaks suggesting formation of amorphous carbon. It was found a high correlation through heating time and peak intensity, by adjusting 2^nd order polynomial curves, R² ranging from 0.96 to 0.99.

Today, perspectives of using the picosecond and femtosecond pulses for biological tissue analysis are limited with several problems. One of them is an absence of direct sources of radiation in water transparency windows, e.g. 1.3 and 1.7 microns. There are several techniques that can produce that kind of radiation. In order to generate it we used synchronous pump and stimulated Raman scattering in a phosphosilicate fiber inside an external cavity. Our work presents the experimental and numerical modeling results for 1.3 micron Raman dissipative soliton generation in an all-fiber system. Additionally, attempts of pulse synchronous amplification are reported.