Nonlocal exciton emission in the two-dimensional material WS2 is an important indicator of dynamics of the system. Spectral shift of the emission is also important, as it indicates regions with different bandgaps, and a smaller bandgap region can 'trap' excitons. We observe both at once using a CCD readout on a spectrometer in which 1D spectral together with 1D spatial measurements are performed. Back-propagation of the slit to the sample indicates the Photo Luminescent (PL) emission region around the excitation spot. A dove prism allows effective rotation of the slit. Quantitative analysis of the spectral and spatial dynamics is discussed.

Hybrid perovskites formed of both organic and inorganic materials in the same crystal unit provide new functionalities otherwise not possible in either organic and inorganic components alone. Due to the ionic nature of these materials, electrons and phonons are strongly coupled and coherent phonons could be excited with ultrashort laser pulses. In this study, using transient absorption spectroscopy measurements, we show that these coherent phonons could be used to manipulate charge transfer in a two-dimensional double perovskite. Findings of this study may serve as a new degree of freedom to consider when designing materials for optoelectronic applications where charge transfer kinetics are crucial.

Surface-enhanced coherent Raman scattering (SE-CRS) promises high signal rates at low molecular concentrations, down to the single molecule limit. Although single molecule SE-CRS has been reached, experiments thus far have been affected by heating effects at plasmonic substrates, which has stifled progress. We discuss a SE-CRS strategy based on dielectric nano-antennas of high index materials, which feature low losses and are thermally more robust than nano-structured metals. We demonstrate molecular SE-CRS signals using Si-based antennas and show improved repeatability, controllability and signal stability.

The selective control of population in the various degrees of freedom in molecules has opened the possibility for unprecedented understanding of reactive potential energy surfaces in gas phase chemical physics. While significant work has been dedicated to understanding, and controlling, the vibrational and translational degrees of molecular freedom, far less attention has been paid to the direct molecular control of rotational energy. In part, this is due to the quantum mechanical selection rules that govern rotational excitation. In this talk an optical molecular centrifuge has been developed and used for extreme rotational excitation of molecules. Coherence beating and energy transfer processes of these super-rotors are followed through coherent nonlinear scattering of the evolving rotational wavepacket.

We present advances in Doppler Raman (DR) microscopy that enable rapid Raman imaging of complex samples. DR spectroscopy is a form of impulsive-stimulated Raman spectroscopy (ISRS), employing a pump-probe excitation. In ISRS, refraction perturbation is generated the pump pulse, imparting a small center frequency shift to the spectrum of the probe pulse. This small frequency shift is converted into a probe pulse timing jitter that is detected by adapted methods of precision timing jitter metrology. We apply this method of high-sensitive ISRS to imaging of complex specimens at high speeds with experimental arrangements that are robust to optical scattering.

Raman spectroscopy is a powerful tool for detecting and identifying molecular structures and chemical bonds in materials. Diverse platforms have been developed to enhance spectroscopic sensitivity. We present a novel doubly enhanced Raman spectroscopy through an optoplasmonic microprobe configuration. The microprobe includes a high-Q whispering-gallery-mode microsphere resonator and nanoplasmonic structures on a substrate with samples sandwiched between them. The optoplasmonic hybrid modes can realize a two-order-of-magnitude improvement over traditional surface-enhanced Raman spectroscopies (SERS), such as commercial SERS test papers. Additionally, 2D Raman imaging is demonstrated by scanning the sample surfaces, showing a new tool for highly sensitive Raman spectroscopy imaging.

We have developed Second Harmonic Generation (SHG) microscope tools to selectively and specifically probe all levels of collagen architecture organization in human ovarian cancer and idiopathic pulmonary fibrosis. We classified normal and diseased tissues in both diseases based on the respective fiber morphology using a novel form of 3D machine learning. We also developed polarization sensitive SHG methods to extract collagen macro/supramolecular structural aspects and found significant differences between normal and healthy tissues. We also present a new theoretical approach to phasematching in biological tissues as an additional characterization method. Collectively, this structural information provides insight into disease etiology.

As light propagates through a multimode fiber, the optical modes exchange power, create new optical frequencies via a complex spatiotemporal non-linear transformation that occurs at relatively low optical powers because of the light confinement and the long interaction length that is possible in a fiber. In this talk, we will review exciting new developments in this field including from our research group. In particular, we show recent results of programming the nonlinear interaction in MMFs for machine learning applications. Several different databases were used to train a system consisting of a multimode fiber of different length/core size of a MMF and a simple, single layer digital network. In several recognition tasks, the classification accuracy that was obtained was comparable to deep, digitally implemented networks. The energy requirement for training and reading the optical system was orders of magnitude less than the digital counterpart.

Femtosecond mode-locked lasers are an essential tool in the physical and life sciences. However, many applications, including 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 Kerr resonators that does not have these limitations. Recent experimental and theoretical studies in fiber Kerr resonators reveal novel pulse parameter scaling-laws and dependencies in resonators based on chirped-pulse solitons, and record-short 120-fs pulses and single-pulse trapping from resonators based on stretched-pulse solitons.

We present time resolved mid-infrared photothermal imaging that allows studying thermal dynamics of samples based on intrinsic vibrational absorption contrast. By using a gated detection in a boxcar configuration, temporal heat profiles at the sub-micron scales can be obtained. Further, the signal to noise is enhanced compared to standard lock-in detection without the need of averaging and post image processing. This imaging platform can be attractive to simultaneously obtain chemical identification and heat diffusion dynamics for a wide range of samples in a label-free manner.

Non-linear optical processes are effective label-free methods for molecular sensing and imaging. An essential consideration for implementing nonlinear optical spectroscopy and imaging is the ultrafast laser source. Applications, such as coherent Raman spectroscopy and imaging, also require wavelength tunability and multiline outputs. Existing solid state systems are complex, costly and bulky. Fiber-based systems, on the other hand, are cost-effective and easier to use. Here we present the development of a divided pulse soliton self-frequency shift source capable of generating multi-line, ultrashort pulses with broadband tunability, while keeping a compact footprint. Recent experimental progress will be discussed.

Ultrafast modulation, switching and optical wave mixing are essential functionalities for various CMOS compatible photonic integrated circuits with applications for optical communication, signal processing and computing. We explore second and third order nonlinear susceptibilities of various inhomogeneous thin film compositions and characterize their properties using a Maker fringes setup and ultrashort femtosecond scale laser pulses. Specifically, we demonstrate enhanced effective second order nonlinear response by engineering the compositions to create a strong internal DC electric fields (~20 pm/V) as well as synthesizing silicon rich silicon nitride films with high second order nonlinear polarizability (~8 pm/V) in as grown films.

Epsilon-near-zero materials are a rapidly expanding field due to their enhanced light matter interaction. These materials have shown large changes in refractive index on the order of the linear index; however, this is associated with large absorption changes. Here we experimentally and theoretically show a method to mitigate the absorption changes in the film while doubling the refractive index modulation. Using beam deflection, a nonlinear technique to measure χ^((3)), individual excitation processes can be controlled in time and space on a film so the nonlinear refractive index change can double on a sample, while the absorption change can be nullified.

Nonlinear optical processes resulting from the interaction of light with matter have provided great opportunities in photonics technologies by enabling spectral control of light. Here, based on first-principles calculations, we investigate the linear and nonlinear optical response of monolayer hBN in the mid-infrared polaritonic region following time-domain and perturbative schemes, from which we conclude an extraordinarily large nonlinear response, which can be modulated by lateral electrical gating and presents an opportunity to achieve quantum blockade at the level of a few quanta. Our study reveals a range of potential applications that include harmonic generation, optical modulation, and quantum information in the mid-infrared range.

An imaging system capable of acquiring high-resolution data at a high speed is in demand. However, the amount of optical information captured by a modern camera is limited by the data transfer bandwidth of electronics, resulting in a reduced spatial and temporal resolution. To overcome this problem, we developed continuously streaming compressed high-speed photography, which can record a dynamic scene with an unprecedented space-bandwidth-time product. By performing compressed imaging in a time-delay-integration manner, we continuously recorded a 0.85 megapixel video at 200 kHz, corresponding to an information flux of 170 gigapixels per second.

Matter under extreme conditions has attracted increasing attention because of its high relevance to many areas including astrophysics, shock physics and inertial confinement fusion experiments. The capabilities of time-resolved diffraction techniques based on X-ray Free Electron Lasers and field-accelerated ultrafast electrons have allowed unprecedented explorations in this area of research, enabling femtosecond visualization of transient atomic dynamics at Ångstrom length scales. In this talk, I will present an overview of our recent work using the technique of single-shot MeV ultrafast-electron diffraction (MeV-UED) to study phase transitions and structural dynamics in ultrafast laser excited solids and liquids under warm dense conditions.

Merging the cutting-edge metaphotonics and the compressive sensing technology, we demonstrate a compact single-shot imaging system enabled by a space-time encoding metasurface - an artificially engineered synthetic surface consisting of nanometer-sized elements that can locally manipulate the time delays of incoming light at the femtosecond scale - for capturing the dynamic properties of ultrafast phenomena and uncovering the unknown or hidden laws that govern such dynamics.

New spatial domain (SD) frequency modulation imaging (SPIFI) architectures are developed that enable the use of the full numerical aperture of long working distance excitation optics without sacrificing the field-of-view. When multiplexed with wavelength domain (WD) SPIFI, multiple advantages follow. One, the WD-SPIFI signals can be used to optimize the multiphoton SD-SPIFI signals. Two, these new SD-SPIFI architectures enable video rate SPIFI. Finally, applications of these new architectures to advanced manufacturing will be presented.

Transient absorption microscopy (TAM) provides imaging contrast from absorptive pigments such as hemeproteins and melanin, based on femtosecond to picosecond-timescale relaxation dynamics. TAM operates by exciting the sample with a short pump pulse, then measuring the time-dependent change in optical absorption, after excitation, with a probe pulse. Here we show that a 520nm pump and 620nm probe provides label-free imaging contrast for hemoglobin, myoglobin, and respiratory chain hemes of mitochondria with sensitivity to redox. We also introduce a simple convolutional neural network for analysis of TAM stacks. Finally, we will discuss future clinical applications to mitochondrial disease.