This PDF file contains the front matter associated with SPIE Proceedings Volume 10903, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Modulation instability (MI) is one of the most nonlinear instability of the focusing nonlinear Schrödinger equation that describes how a low amplitude noise on an input signal can be exponentially amplified to create high-intensity localised structures. Recently, MI has attracted renewed attention due to its potential link with the development of extreme events or rogue waves, and many theoretical, numerical and experimental studies have been reported in various physical systems including optics and hydrodynamics. A particular difficulty associated with experimental studies of MI in optics is the need for real-time measurement techniques. In the time domain, the time-lens approach is complex and constrains the measurement bandwidth and power. In the spectral domain, the dispersive Fourier transform is simpler but only typically allows for low dynamic range measurements and does not provide information about the associated temporal properties. We report on our recent work on the use of machine learning to predict from real-time spectral data statistics for the maximum intensity of the localised temporal peaks in a fibre-optic chaotic MI field, peaks which are preferentially associated with extreme events. We subsequently train a neural network to correlate the spectral and temporal properties using data from numerical simulations and we use this model to predict the temporal probability distribution based on near 60 dB dynamic range real-time spectral data from experiments. These results open novel perspectives in all systems exhibiting chaos and instability where direct time-domain observations are difficult.

Real-time measurements are now mature enough to cover a wide span of applications from fundamental laser physics and dynamics to applied sciences. In this talk, we focus on the application of time-stretch techniques for the ultrafast imaging of non-repetitive ultrafast events. In particular, we show that amplified time-stretch imaging fills the gap between ultra-high frame rate imaging techniques (burst-mode and/or temporal mapping cameras) and continuous imagers (CCD/CMOS) as it allows MHz frame rates on long - ms - timescales. As an illustration, we demonstrate the real-time tracking - i.e. propagation and reflection - of single laser-induced shockwaves (SWs) with velocities exceeding a few km/s and show that it allows, on the one hand, to monitor its full dynamics, from its deceleration to the observation of the plasma contact wave, and, on the other hand, to easily acquire intensity and velocity statistics on large ensembles of SWs [1]. This study has numerous potential applications in applied physics e.g. in the study of transient phenomena in pulsed laser-material interactions as these dynamics indeed strongly impact many scientific fields such as micromachining, material analysis or high-harmonics generation, to name a few. We also report the use of 1-D amplified time-stretch imaging to capture the rupture of liquid ligaments, which could bring new insights in two-phase flows physics. [1] Hanzard et al., Appl. Phys. Lett. 112, 161106 (2018)

KALYPSO is a novel detector operating at line rates above 10 Mfps. The detector board holds a silicon or InGaAs linear array sensor with spectral sensitivity ranging from 400 nm to 2600 nm. The sensor is connected to a cutting-edge, custom designed, ASIC readout chip, which is responsible for the remarkable frame rate. The FPGA readout architecture enables continuous data acquisition and processing in real time. This detector is currently employed in many synchrotron facilities for beam diagnostics and for the characterization of self-built Ytterbium-doped fiber laser emitting around 1050 nm with a bandwidth of 40 nm.

A bottleneck for the investigation of electron beam dynamics in ring accelerators is a fast detection scheme coping with their high repetition rates in the MHz range. For example, at KARA (KArlsruhe Research Accelerator), the electron storage ring at the Karlsruhe Institute of Technology (KIT) in Germany, we showed that electro-optical methods enable single-shot detection of longitudinal electron bunch profiles by imprinting them onto chirped laser pulses. However, commercial cameras required to detect the spectra are typically limited to hundreds of kHz in readout speed. To tackle these challenges, we developed KALYPSO (KArlsruhe Linear array detector for MHz-rePetition rate SpectrOscopy), a linear detector array with a data acquisition system (DAQ) allowing high data-rates over long time scales. Due to a modular approach, various sensors (InGaAs and Si) can be used, so that KALYPSO can be adapted to different experiments with spectral regimes ranging from near-ultraviolet (NUV) to near-infrared (NIR). In this talk, we present recent results on studies of longitudinal and horizontal bunch profiles using KALYPSO. As an outlook, we give another example for MHz-range readout using KALYPSO, namely horizontal bunch profile diagnostics measuring the radiation emitted from a dispersive section in a storage ring. At the KARA visible light diagnostics (VLD) port the emitted radiation above 400 nm was previously recorded with a fast-gated camera. Here, limitations are the repetition rate in combination with the huge number of cycles during continuous measurements. To overcome these limitations, KALYPSO can repleace the fast-gated camera. Furthermore, due to the easy implementation of KALYPSO, we envision numerous applications for table-top experiments as well as for large-scale facilies.

The Accelerator for the European X-Ray Free Electron Laser delivers femtosecond electron bunches at an energy of currently 14GeV at a repetition rate of up to 4.5MHz in bursts of up to 2700 pulses every 100ms to distribute them between different undulator beamlines. The emitted femtosecond x-ray laser pulses at wavelengths between 0.05nm and 6nm can serve up to three experiments in parallel. To measure the longitudinal bunch profile of the electron bunches, three detection systems based on electro-optical spectral decoding have been installed and are currently being commissioned. The systems are capable of recording individual longitudinal bunch profiles of all bunches in a burst with sub-ps resolution at a bunch repetition rate of 1.1 MHz, sampling the electron Coulomb field with laser pulses at 1030nm. A short detector latency of about 10µs also gives the prerequisites to establish a fast intra-burst feedback to stabilize the bunch profile. Bunch lengths and arrival times of entire bunch trains with single-bunch resolution have been measured as well as jitter and drifts for consecutive bunch trains. For comparison of detection techniques at one position, the laser signal is split and measured with a time-stretch setup in parallel.

We evaluated the capabilities of an intense ultrafast high-harmonic seeded soft X-ray laser at 32.8 nm wavelength regarding single-shot lensless imaging and ptychography. Additionally the wave front at the exit of the laser plasma amplifier is monitored in amplitude and phase using high resolution ptychography and backpropagation techniques.Characterizing the laser plasma amplifier performance depending on the arrival time of the seed pulse with respect to pump pulses provides insight into the light plasma interaction in the soft X-ray range.

High-speed optical measurement systems are wholly constrained by the number of measurements that can be acquired in a limited amount of time. Unfortunately, most of these painstakingly acquired measurements are wasted collecting much more data than is required to accurately determine a given signal of interest. Specifically, real-world signals (e.g. images) are highly compressible and can be accurately represented by relatively few significant coefficients in an appropriate mathematical basis. Traditionally a signal is sampled in the physical domain according to the Nyquist theorem to acquire a raw digital representation and then a compression algorithm is applied, which eliminates as much of the redundancy in the original data as possible. Hence, most of the acquired data is essentially thrown away and, consequently, for most applications in high-speed measurement the raw data bandwidth is far larger than is truly necessary. In this talk, we will discuss our recent research in applying optical signal processing and compressed sensing to enhance performance in such high-speed measurement-limited applications. Compressed sensing is a recent and influential sampling paradigm that advocates a more efficient signal acquisition process by implementing image compression directly in the physical layer. Specifically, we will discuss our research into constructing compressed sensing based optical hardware systems for high-throughput microscopy, optical coherence tomography, LIDAR, and hyperspectral imaging.

Ghost imaging is an unconventional imaging technique that generates high resolution images by correlating the intensity of two light beams, neither of which independently contains useful information about the shape of the object. It has been shown that ghost imaging has great potential to provide robust imaging solutions in the presence of environmental perturbations. Originally demonstrated in the spatial domain with entangled photons, ghost imaging has been subsequently extended to the use of classical incoherent light sources. Significantly, the fundamental principle of ghost imaging is not restricted to producing spatial images, and in a recent time-domain application, measurement of ultrafast signals on picosecond timescales was reported. Here, exploiting recent progress in ultrafast real-time measurement techniques, we perform the first demonstration of ghost imaging in the spectral domain. Specifically, we show that, by correlating the spectral fluctuations of an incoherent supercontinuum light source measured in real-time using the dispersive Fourier transform with the total (integrated) signal detected after an object, one can obtain the spectral signature of this object. As a particular application, we report on the spectroscopic measurements of methane absorption lines in the near-infrared over a 50 nm bandwidth and with sub-nm resolution. The method is broadband, scan-free, has rapid acquisition time, and requires neither a high-power source nor particularly sensitive detectors. The results are in excellent agreement with independent direct measurements and offer novel perspectives for remote sensing in low light conditions, or in spectral regions where sensitive detectors are lacking.

We investigated the vectorial nature of ultrafast rogue waves in fiber lasers. In this proceeding, we present the analytical evolution of the nonlinear Schroedinger equation in vector field and show that when considering two Solitons with different state of polarization, they do not stay static which indicates that such Solitons are not a solution of the system.

Pulse-by-pulse single-shot spectrum measurement can be realized using the time stretch dispersive Fourier Transform technique. In this paper, we report a fully integrated and modular pulse-by-pulse single-shot optical spectrum analyzer (PS-OSA) system. Many modules including a picosecond gain-switched laser, multiple fibers with different chromatic dispersions, high-power optical amplifiers, a clock-generator, a photodetector and a digitizer are integrated into a main-frame. These modules are standard in size and can be replaced to improve the performance or changed to adapt the system to different applications. Here, we present the specification of this single-platform PS-OSA and successfully demonstrate high throughput measurement of the transmission spectrum of electroabsorption optical modulators with 11.7 ns refresh time.

To investigate changes of ultrafast dynamics during irreversible phase change in phase change materials Ge2Sb2Te5, we performed high-repetition-rate singleshot pump-probe spectroscopy using a combination of time-encoding and timestretching methods. By measuring the pump-probe traces while ramping the pump intensity, we observed a clear change in the ultrafast pump-probe dynamics after the phase change. Correlation between the ultrafast dynamics in the femtosecond timescale and the amount of phase change observed in millisecond timescale indicates that accumulation of the excited states in the sample plays an important role in the acceleration of the phase change. The result clearly demonstrates the usefulness of our method, which could be applied to the investigation of multi-timescale dynamics in various irreversible phenomena. Improved signal-to-noise ratio and the variable time-window of the single-shot pumpprobe measurements were also demonstrated using a grating pair and a chirped fiber Bragg grating.

Concatenating fibers to extend supercontinuum generation beyond the multiphonon absorption edge of silica to access longer wavelengths in the mid infrared region has received much attention due to the various molecular fingerprints that exist in this region. Thulium doped (Tm) fiber has been used as an intermediate fiber to get above the multiphonon absorption edge of silica through absorption (900 and 1600 nm) and emission processes between (1800 – 2100 nm) and (2200 - 2600 nm). The advantages of the Tm-doped fiber is not only limited to generating SC above the multiphonon edge of silica but also reducing the high peak power which easily damages the facet of soft glass fibers whose transmission window extends well into the longer mid infrared region. The mechanisms governing the generation of SC in active fibers is quite different from passive fibers as there is interplay of the nonlinear processes that are commonly observed in passive fibers as well as energy transition contributions by the dopants in the fiber. SC generation and its application are hindered by pulse-to-pulse fluctuations as the generation is initiated by noise seeded processes especially in the long pumped regime (> 1ps). In this work we have experimentally studied the pulse fluctuations in thulium gain fiber whose SC spans 1550 – 2700 nm at three different repetition rates (10 KHz , 100 KHz, 200 KHz). We have illustrated the relative intensity noise across the whole spectrum most importantly within the absorption and emission regions of the Tm-doped fiber.

The capability to produce femtosecond laser pulses with wavelengths in the atmospheric absorption window requires a new understanding of pulse propagation effects. In this work, we characterize the changes in temporal propagation of middle infrared femtosecond laser pulses by cross-correlation frequency resolved optical gating (XFROG). The temporally distorted infrared pulses are cross-correlated with 800 nm pulses by a four-wave mixing process in air. For the first time, we investigate these propagation effects through gas molecules that are not present in the atmosphere. Each molecule is shown to have a unique effect on the temporal propagation of the pulse that is wavelength dependent. We verify our experimental data with simulations based on a KramersKronig transformation of spectral data from the HITRAN database. The propagation effects are similar to optical free induction decay. Multiple vibrational and rovibrational absorption lines are excited by the middle infrared pulse and constructive interference occurs at various delay times relative to the initial pulse. The constructive interference impresses a unique fingerprint onto the pulse because the spectral lines of each molecule are unique. The fingerprint behaves as a nonlinear function related to the molecular concentration. To account for this, a regression model is developed to predict the concentration of unknown gas species. The middle infrared beam is the only laser beam sensitive to the analytes. Thus, standoff detection is a possibility since the XFROG can be performed locally.

We report the surprising observation of yellow to red visible light flashes in the splice point connecting the seed stage to the power amplifier in a high power, narrow-linewidth, polarisation-maintaining Ytterbium doped fiber laser. The multistage laser delivers upto 500W of power with a tuneable linewidth between 2.88 GHz to 9.88 GHz at 1064 nm. For different linewidths, the visible flashes were observed at different power levels of the laser. We observed a strong correlation between these flashes to the appearance of backward pulses with the onset of Stimulated Brillouin Scattering (SBS). We identify the cause for the flashes to be a two part phenomena. Beyond a threshold level, SBS results in the formation of high peak power pulses. These pulses undergo cascaded Raman scattering into higher order stoke wavelengths. These higher order pulses are unaffected by the isolator separating the amplifier stages and moves back into the seed stage with lower effective area, higher NA fibers. We recently demonstrated that 2nd and 3rd harmonic generation can occur in high NA, low effective area fibers assisted by Cherenkov-type phase matching between core light in the NIR and cladding light in the visible. Through processing of the images of the flash acquired with high resolution, we identified the wavelengths to be a mixture of the second harmonic components of the 2nd and 3rd order Raman Stokes of the 1064 nm laser wavelength (1175nm/588nm and 1240nm/620nm). We anticipate the use of these flashes as a potential monitor for the onset of SBS.

In this proceeding, we describe in details our experimental setup and the free-space scheme which enable us to develop advanced time-lenses. We compare different methods for preparing the pump pulses and explain their pros and cons. Specifically, we show that when assembling the time-lens in free space, the system has lower losses which result in higher efficiency and thus less amplifiers. Since we do not need as many amplifiers, the noise level is lower and we can detect weaker signals.

Optical cavitation is the formation of vapor cavities in a liquid when a pulsed laser is focused over highly absorbent liquid; however, when a continuous laser is used, the phenomenon is called thermo-cavitation. Recently, thermocavitation has been studied in different materials^1–3. In this work, we present the analysis of extra-cavity pulses generation by thermo-cavitation induced by a CW laser beam focused into solutions of Hibiscus Sabdariffa in ethanol and Hibiscus Sabdariffa in methanol. Due to the high absorption of the natural dye and the low boiling point of the solvents (< boiling point of the water), heating is produced which gives origin and implosion of bubbles. The process of explosion and implosion of the bubbles acts as an obturator allowing the pulses formation of the light passing through the sample. The characterization of the pulses was performed by moving the sample around the focus of the lens, we observe a modification in the thermo-cavitation time, an analysis of the changes in the frequency rate and the amplitude of pulses was performed. The frequency rate, the amplitude, and the full width half maximum (FWHM) of the pulses were measured. We found that the average frequency decreases, and the average amplitude increases when we move the sample at a distance from the focus. The temporary response of the pulses obtained in both solutions, change as a consequence of the difference between the boiling point of the methanol and ethanol.

We demonstrate a novel algorithmic approach for second-harmonic-generation (SHG) frequency-resolved optical gating (FROG) that always converges and is also faster for complex pulses. It takes advantage of the Paley-Weiner Theorem for generating significantly better initial guesses. It also uses a multi-grid approach, which allows the algorithm to operate initially on smaller arrays for early iterations and only on the complete array for the final few iterations. We tested it on sets of twenty thousand noisy FROG traces and have achieved 100% convergence even for pulses with time-bandwidth products of 100.

We demonstrated distributed strain measurement using the slope-assisted Brillouin optical correlation-domain analysis (SA-BOCDA) with polarization maintaining fiber (PMF), which has no polarization scrambler. The 0.35- m-long strained section in 47-m-long PMF was clearly measured with 1-kHz sampling ratio and no averaging. Next, we proposed the new concept of the human interactive sound effector using SA-BOCDA with PMF, which means that the distributed measurement data was used as sound waveform directly. Then we demonstrated the sound wave controlling with SA-BOCDA with PMF. This result will be useful for not only the sensing application but also the musical instrument application based on nonlinear optical phenomenon.

Optical spatial solitons have been subject of intense research over the past years due to their natural potential to control light by light and become essential for the future of all-optical technologies. We report soliton solutions in optical lattices completely described by Hermite-Gaussian beams for the (1+1)D case that are stable if their power remains below a critical threshold value. The pure local nonlinear system studied here can mimic, up to certain extent, a strongly nonlocal medium. We conclude that our methodology of imposing an optical lattice as a restriction on the nonlinear Schrödinger equation can be used to generate new families of solutions by taking advantage of different restrictions.

Self-injection locking - an efficient method to improve the spectral performance of semiconductor lasers without active stabilization - has already demonstrated its high potential for operation with single-longitude-mode fiber lasers. Recently, we demonstrated that self-injection locking of a conventional DFB laser through an external fiber optic ring cavity causes a drastic decrease of the laser linewidth and makes possible its direct application in a phase-sensitive optical time domain reflectometry (φ-OTDR) acoustic sensor system. Detection and localization of dynamic perturbations in the optical fiber were successfully demonstrated at the distance of 9270 m. However, the ability of the system to restore the perturbating frequency spectrum was not quantified. Here, we have evaluated the performance of a φ-OTDR system for acoustic/vibration measurements utilizing a conventional telecom DFB laser self-stabilized through an external PM optical fiber ring resonator. The use of PM fiber components prevents the polarization mode-hopping that is proved to be a major source of the laser instability, resulting in single frequency laser operation with 6 kHz linewidth. The laser diode current and the laser fiber configuration temperature both have been stabilized with accuracies better than 0.3%. All laser components have been placed into a special insulating box to protect the laser from external perturbations. Under these conditions, the typical duration of laser operation in self-maintaining stabilization regime is ~30 minutes. The laser long-term frequency drift is estimated to be less than ~30 MHz/min. This low-cost solution is directly compared with the use of a commercial, ultra-narrow linewidth (~ 100 Hz) fiber laser implemented into the same setup. Both systems are tested for measurement of the frequency of vibration applied to a fiber at a distance of 3500 m. The obtained SNR value higher than 6 dB demonstrates the ability of the DFB laser to be used in distributed measurements of vibrations with frequencies up to 5600 Hz with a spatial resolution of 10 meters.