We study nonlinear collective behaviors in periodic arrays of silver spherical nanoparticles embedded into a silica matrix, that are excited normally by an external field with the frequency close to the frequency of the localized surface plasmon resonance.

Temporal optics, and specifically time-lenses and time-stretch systems, revolutionized the field of ultrafast measurements. Over the last years, we utilized time-lenses to measure different quantum schemes and studied the temporal modes of correlated photons with high temporal resolution. We developed temporal schemes based on quantum light, for realizing quantum tomography in the time-domain. We developed low-resolution time-lenses for weak quantum measurements. Finally, we suggest how quantum time-lens can lead to optical deep learning systems. In the talk, I will give an overview of the different types of quantum temporal schemes, elaborate on the future challenges in the field, and discuss the prospects and future applications which may be possible.

Time-lenses can image ultrafast signals in time. Placing them in a 2-f configuration leads to Fourier transform of the input signal and ultrafast spectroscopy. We utilized two time-lenses in a 4-f configuration and formed an interferometer in the time domain. Our time lenses are based on four-wave mixing process, generating an idler beam which serves as the output. The output from the first time-lens is the input to the second time-lens. At the output of the second time-lens, we get an interference between the signal beams of both time-lenses and the idler beams of both time-lenses. This interference is sensitive to ultrafast phase shifts in time and can lead to interfere signals in different times. This interferometer is good for quantum imaging, and studying the temporal structure of entangled photons. In this talk we will demonstrate the interferometer, how we exploit time-lenses for interferometry, the application of the interferometer, and our experimental results.

We introduce an ultralow latency computing technique that utilizes femtosecond pulses for the classification of optical data. Spectral mapping of data onto femtosecond pulses and transformation utilizing the Nonlinear Schrodinger Kernel reduces the latency in data classification by several orders of magnitude and increases inference accuracy in experiments. Closed-loop optimization and training of the optical nonlinearities is achieved using spectral phase-encoding and leads to improvement in the accuracy of data classification in time-stretch microscopy.

Sending an ultrafast pulse in multimode fiber can lead to nonlinear interactions between the modes. When sending such a pulse in graded-index fibers there are cases where all the energy is transferring from the high-order modes into the lowest one. This effect is called modal self-cleaning. We developed a multimode time-lens, which measures the temporal and spatial dynamics of ultrafast signals in multimode fibers. With our system, we can detect the dynamics of each mode in time with high temporal resolution, and identify which mode is coupled to which and how the energy transfers between them. In this talk, We will present our measurement system in details and describe our novel results on modal self-cleaning. We will also comment on other multimode effects which our system can measure for the first time.

Whispering gallery mode microresonators are excellent devices to observe nonlinear optical effects at extremely low threshold powers. This talk will present recent results from our research group on optical frequency comb generation in these devices. This includes work on frequency combs with dark and bright solitons, microcomb-based generation of stabilized THz signals, and the spectral extension of frequency combs using multiple seed lasers. In addition we investigate the nonlinear interaction of counterpropagating light in microresonators.

We investigate quantum cascade lasers emitting in the THz range based on a new, planarized waveguide platform. We measure temporal intensity profile by means of Shifted Wave Interference Fourier Transform Spectroscopy (SWIFTs) of both Fabry-Pérot and ring resonators. We observe a variety of phemomena varying the amount of microwave injected in the laser cavities. In Fabry-Pèrot devices we observe transition from FM comb behaviour to AM with pulses formation as short as 4.4 ps. Additionally, we measure with SWIFTS fundamental as well as harmonic comb states under RF injection. In the case of the ring lasers, we fabricate devices displaying spectrally dependent dispersion. We observe hysterical behaviour of the lasing spectra as a function of the RF power. In the case of very weak RF injection, we observe pulses and spectral envelopes well fitted by a sech^2 profile corresponding to anomalous dispersion region, hinting at the presence of solitons.

Coherent Raman scattering (CRS) microscopy is a powerful third-order nonlinear optical technique for label-free chemical identification of molecules based on their intrinsic vibrational spectrum. It can reach video-rate imaging speed and detect very dilute species. I will review the working principles and state of the art of this technique, presenting our recent results and perspectives. I will also show how artificial intelligence methods can be employed effectively to increase the signal-to-noise ratio and extract the relevant information from the large experimental hyperspectral datacubes.

Raman spectra provide a rich and powerful label-free probe of biological systems. While the narrow spectral features make Raman spectroscopy extremely attractive, the weak strength of Raman scattering makes it difficult to deeply in many situations. Low frequency Raman scattering spectroscopy provides the potential for probing macromolecular and local material properties. Until recently, the acquisition of such low frequency Raman spectra has been limited by technical challenges. We will discuss newly developed tools that allow for high-speed time-domain Raman spectroscopy of low and fingerprint region Raman spectra. Imaging performance and robustness of the signal to scattering will also be discussed.

We recently discovered a novel ultrafast coupling mechanism of femtosecond solitons via coherent optical phonons inside a solid-state laser cavity, forming stably bound states - “Soliton molecules”[1]. Moreover, preceding the stable binding, the relative motion of two solitons can be harnessed to sample THz phonons using real-time spectroscopy within a single rapid all-optical delay sweep. In this contribution, we discuss the sampling and contrast mechanism for highspeed spectroscopy and compare the scheme to conventional extra-cavity time-domain Raman sampling schemes. [1] A. Völkel et al., Intracavity Raman Scattering couples Soliton Molecules with Terahertz Phonons, Nature Comms. 13 (1) (2022)

Recording complex terahertz pulse shapes in single-shot is needed in various applications, ranging from terahertz time-domain spectroscopy to real-time accelerator diagnostics. Among existing solutions, association of photonic time-stretch with electro-optic detection has been shown to provide the highest repetition rates. However a fundamental bottleneck in time resolution and bandwidth has severely limited those strategies so far. We present here the first demonstration of a time-stretch ADC, that is no more subjected to this time-resolution limit, by using the DEOS (Diversity Electro-Optic Sampling) reconstruction method [1]. Experiments are performed on the ELBE intense Terahertz source. [1] Roussel et al., Light Science & Applications 11, 14 (2022) https://doi.org/10.1038/s41377-021-00696-2

Multi-pass optical and electron microscopes outperform standard single-pass instruments in dose-limited regimes and have been shown to be quantum optimal. We report on recent progress towards demonstrating multi-pass transmission electron microscopy with a focus on the electron gun and monochromator system. Prompt electron emission from a Schottky emitter is laser-triggered with nanosecond optical pulses, and a single-photon emission process can be used to generate high current pulses with narrow intrinsic energy spreads. These pulse properties could be useful for nanosecond time-resolved and potentially single-shot microscopy experiments and are well-suited for use in a multi-pass transmission electron microscope.

Countless ultrafast imaging techniques have been developed and even though they brought significant insights, their application out of a laboratory environment is however often quite limited, either by the complexity of operation or by a heavy data processing. We demonstrate flexible single-shot imaging via the combination of sequentially timed all-optical mapping photography with acousto-optics programmable dispersive filtering and digital in-line holography. The frame rate and exposure time can be independently adjusted without complex shaping stages, making the system remarkably agile. In-line holography allows to achieve an even higher simplicity through its lensless operation and the reconstruction on a wide depth of field.

Ultrafast pulsed lasers are integral for a variety of industrial, medical, and scientific endeavors. Fundamentally, pulsed lasers are complicated four-dimensional space-time phenomena that can be described by their complex spatiotemporal electric field profiles. Here we present the first ever single-shot, full-field, reference-free spatiotemporal pulse-beam measurement system capable of single-pulse characterization. Our technique combines single-shot spatiospectral characterization from broadband single-shot ptychography (BBSSP) with a collocated single-shot spectral phase measurement from single-shot frequency resolved optical gating (SSFROG). Together, these measurements provide the full complex spatiospectral field at the plane, which can be computationally propagated and Fourier transformed to provide the spatiotemporal profile of the pulse at any plane.

High frame rate (HFR) phase-and-amplitude contrast imaging is imperative for a better understanding of the underlying physics in dynamically evolving phenomena. Here we present, to our knowledge, the first experimental HFR ptychographic reconstructions using a novel Time-Resolved Imaging via Multiplexed Ptychography (TIMP) system. Our TIMP system is composed of a time-encoding device, which creates a train of temporally separated pulses of different phase profiles, and a novel beam-sampling single-shot ptychography microscope. HFR imaging is achieved by reconstructing the complex object from each pulse independently and time ordering the reconstructed objects based on the phase structure of the reconstructed probes.