Feedback systems have been utilized to reduce the possible thermal side effects of lasers for surgery by means of temperature monitoring to control irrigation systems. In this study, we investigated the potential application of optical coherence tomography as a means of detecting bone dehydration status. We investigated the penetration depth of the OCT laser and its respective relation to the hydration status of bone. A deep-learning method was utilized to differentiate between different levels of water content in bone tissue (fresh/hydrated, dehydrated, and carbonized) based on the OCT images. The proposed model achieved an accuracy of 0.912 on an independent test set, demonstrating its ability to accurately predict the state of the bone considering these three conditions. We believe this method can potentially accelerate the detection of dehydration during laser surgery, improving the safety of using lasers with real-time feedback.

Photoemission in modern high-brightness electron sources is under study at the DESY-PITZ photo injector. The electron source optimization process is under continuous upgrading. The developments in modern digital signal processing provide an opportunity for building intelligent algorithms that implement mathematical methods unattainable by analogue technology which can support the related image of emittance measurements from PITZ system. In this work, we provide an intriguing technique for designing multilayer FIR filters with minimal computing effort. As a result, the filter design is particularly effective at reducing complicated noise and performs quickly and efficiently.

Selective Emitters (SEs) are the main components of solar thermophotovoltaic (STPV) systems; they act as intermediate thermal radiation emitters to shape the incident solar spectrum to match the wavelengths useful for the PV cell. In this work, we present the design, optimisation, fabrication, and characterisation of an SE based on a multilayer design made of SiNx, SiO2, and TiO2 layers. The SE is optimised to work with PV cells based on III-V semiconductors, such as GaSb, InGaAs, and InGaAsS, the bests suitable for SPTV applications. The fabricated SE shows an emitter efficiency (ηSE) of 50% if matched with a PV cell with an energy bandgap of 0.63 eV.

In this work, we present proof of concept of a Raman based distributed temperature sensor using standard telecommunication fiber as the sensing element. To allow coexistence with data transmission, a pump source with a wavelength of 1064 nm is used. The proposed DTS is characterized in the range of 20 °C to 100 °C, using the ratio between the Raman band’s powers linearized. We established a characteristic curve of the sensor with a sensitivity of 0.0018±0.0001 /°C, showing that the proposed DTS can detect temperature variations. This work is the first step forward in the development of distributed sensors that coexist with data transmission over the same optical fiber.

Recent results of a long-term effort of Tomsk-Reims research teams on accurate intensity data obtained from high-resolution absorption spectra of ozone suitable for the atmospheric remote sensing in a wide IR range are summarized. This includes vibronic bands corresponding to the transitions towards triplet electronic states near 1 micron, and vibration-rotation bands covering the far-infrared and near-infrared ranges.

Quantitative and Material-specific Nanoscale imaging with Table-top High Harmonic Sources

Passive modelocking (PML) of lasers is pivotal in modern science and industry. Here, solving a half-century-long challenge, we present the first master equation (ME) describing PML on all time scales, from Q-switched to fundamental and harmonic modelocking, valid for both slow and fast saturable absorption and short and long cavities. The proposed ME should become the workhorse for analytical and numerical studies of ultrafast lasers in both the photonics engineering and laser physics communities.

We present here an experimental demonstration of a new method to access the multi-pulse regime in mode-locked fibre laser. This method allows us to drastically reduce the pumping power, while having a stable train of multiple pulses.

Predicting complex nonlinear dynamical systems has been even more urgent because of the emergence of extreme events such as earthquakes, volcanic eruptions, extreme weather events (lightning, hurricanes/cyclones, blizzards, tornadoes), and giant oceanic rogue waves, to mention a few. The recent milestones in the machine learning framework offer a new prospect in this area. For a high dimensional chaotic system, increasing the system’s size causes an augmentation of the complexity and, finally, the size of the artificial neural network. Here, we propose a new supervised machine learning strategy to locally forecast bursts occurring in the turbulent regime of a fiber ring cavity.

The targeted generation of fs pulses is essential for a variety of applications and it is routinely carried out by 4f pulse shapers. However, this seemingly simple task is complicated by hidden experimental limitations, such as modulator crosstalk or pixelation. We present an approach to overcome this issue by using a high-precision phase plate with a phase change characterized with /500 precision. We generated pseudorandom pulses using a 4f pulse shaper by using a structured PMMA plate with the high-precision predefined shape made by the SPDT machine. We study the accuracy, reproducibility, as well as the sufficiency, and limits of the method. The generated pulses are characterized using the FROG method. The reconstructed pulses’ shapes and their spectral phases are compared to the results of simulations.

The impact of the amount of nonlinearity per focal pass on the beam quality in gas-filled Herriott-type multipass cells (MPCs) is investigated. Through the variation of the gas pressure, the peak nonlinear phase shifts per focal pass was varied from 0.8 rad up to 5.9 rad, which is the highest value demonstrated in a MPC. Simultaneous monitoring of the effective homogeneity [1] and M² revealed no degradation of either. Supported by numeric simulations the findings suggest that the nonlinearity per focal pass in gas-filled MPCs below the self-focusing limit is not limited by spatio-spectral couplings. The presented findings become especially important for challenging regimes such as high compression factors and few-cycle pulses. Here the reduction of passes can significantly boost the transmission and optimized designs may enable the technology to move towards the single-cycle regime.

Silicon photonics has been largely developed as a platform to address the future challenges in several applications including datacom, sensing or optical communications, among others. However, the properties of silicon itself is not enough to overcome all limitations in terms of speed, power consumption and scalability. Especially, silicon exhibits strong two photon absorption (TPA) and is centrosymmetric limiting the use of its nonlinear optical properties including Kerr and Pockels effects. New strategies have then been encouraged based on the heterogeneous integration of new materials in the silicon photonics platform. In this perspective, the recent trends in the development of new materials with optical properties complementary to the silicon and silicon nitride properties will be presented. In particular, the presentation will focus in a new integration approach of doped crystalline-oxides on silicon and silicon nitride photonics platform. Especially, the integration of doped-zirconia (ZrO2), compatible with CMOS technology has been developed. Indeed, such an oxide exhibits linear and nonlinear optical properties suitable to address the challenges of silicon photonics: low propagation loss, no two-photon absorption (TPA) due to its large bandgap energy, a large transparency window from the ultraviolet to the mid-infrared, Kerr and Pockels effect, and light emission.

We study the antimony trisulfide’s (Sb2S3) linear optical properties for potential applications in reconfigurable chip-based supercontinuum mid-IR sources. We experimentally demonstrate that Sb2S3 cladding on SiGe-on-Si waveguides induces relatively low extra propagation loss below 1 dB/cm between 3.3 and 3.9 μm wavelength.

Since their first demonstration more than 15 years ago, subwavelength metamaterials in silicon photonic devices have attracted increasing research interest while also breaking into commercial applications. We will discuss recent advances in this research field, in particular novel components and circuits for beam steering applications, on-chip filtering and quantum optics. The use of Mie resonant particle chains as on-chip waveguides has only recently been demonstrated and is opening the door to a new and exciting branch of integrated metamaterials research. We will review the early work in this area.

Recently, we successfully realized amorphous silicon carbide (a-SiC) integrated photonics with

optical losses as low as 0.78 dB/cm. Moreover, the deposition of a-SiC was done at 150 ℃, which enables

successful lift of a-SiC as an additive step to existing photonics circuits. In this work, we present an adiabatic

taper coupler which provides bidirectional lossless connection between two integrated photonics platforms:

thin-film silicon nitride (Si3N4) and a-SiC. Normalized power transmission of 96.61% is presented, and the

coupler enables strong confinement when coupling from weakly confined thin-film device to normal thickness

device. By utilizing such a coupler as bridge, switching back and forth between Si3N4 and a-SiC platforms

can be easily realized. This allow us to carry out applications including quantum interference and digital

Fourier spectroscopy, in which long optical delay lines are constructed on Si3N4 and highly integrated circuits

are built on a-SiC.

The longwave infrared and terahertz bands present unique obstacles for the generation of compact broadband frequency combs. I will discuss some of our work that aims to address this grand challenge, focusing on two types of combs. First, I will discuss our work on quantum cascade laser-based frequency combs, light sources that are able to directly generate broadband combs through an active cavity nonlinearity. In particular, I will discuss how our work on terahertz combs led to the discovery of frequency-modulated combs, a fundamental comb state that can manifest in any laser at any wavelength. This mode of operation is well-suited for efficient and broadband comb generation in semiconductor lasers. Following this, I will discuss some of our recent work on low-loss passive photonic platforms in the longwave infrared based on hybrid photonic integration. This approach allowed us to create optical microresonators in the longwave infrared with quality factors two orders of magnitude better than the state-of-the-art, offering a promising direction for the production of broadband microresonator-based solitons.

Inverse design is used to spectrally shape Kerr microcombs via dispersion

optimization. We experimentally demonstrate flexible ‘meta’ dispersion control using

selective multimode hybridization in photonic crystal ring resonators, and present initial

comb shaping results.

Frequency combs (FC) generated by quantum cascade lasers (QCLs) are a promising tool for precision spectroscopy and gas sensing. Recently, ring QCLs have emerged as a new platform for generating FC with unique advantages over Fabry-Perot geometry. While the bandwidth of such Fabry-Perot devices is determined by the device geometry and dispersion, radio-frequency injected devices with circular geometry enable the exploitation of the full gain bandwidth in a controlled manner. Together with this platform, a predictive analytical model that shows excellent agreement with the experimental data was developed. Our results pave the way for a new approach for frequency comb generation based on fast-gain saturation.

Locking multiple modes into a frequency comb is key for multiple metrological applications, and a great effort has been therefore invested in this challenge over the last decade. The most common techniques are based on either nonlinearities or modulation of the cavity, while the latter is considered the more controllable method to produce frequency combs. The modulation couples cavity modes and creates a lattice in a synthetic dimension with coherent walk dynamics, but typically these dynamics are overthrown by the dissipative processes, leading to a spectrum that is narrow relatively to the full frequency ladder potential. Here we propose and demonstrate that by using fast-gain we preserve the full potential of the coherent walk and lock the frequency comb at its maximum possible bandwidth. Moreover, we find in our system a unique regime of dissipative fast-gain Bloch oscillations. We demonstrate these dynamics in RF-modulated quantum cascade laser ring devices.

We present a dual-comb spectrometer based on quantum cascade lasers operating at 7.7 µm with a stabilization scheme that enables coherent averaging. We show that by illuminating a low cost near-infrared light source of the front facet of the quantum cascade laser, we can tightly lock one comb line of the dual-comb spectrum, resulting in narrow linewidth with sub-radian integrated phase noise for all RF comb lines.

Nonlinear random waves exhibit a phenomenon of irreversible thermalization, in analogy with the thermalization of a classical gas system. This irreversible process of thermalization to the Rayleigh-Jeans equilibrium distribution has been recently observed experimentally in multimode optical fibers. Here we discuss a recent progress along two different directions. Firstly, we report the observation of thermalization to negative temperature equilibrium states, in which high-order fiber modes are more populated than low-order modes. Secondly, we analyze the impact of disorder inherent to light propagation in multimode fibers. We identify an unexpected regime in which strong random coupling among non-degenerate modes leads to a nonequilibrium process of thermalization.

We study experimentally the spatial coherence across the full spatial beam profile of supercontinuum light generated in both in graded-index and step-index multimode fibers. We observe a decrease of the coherence area with an increase of the injected pump power. Numerical simulations based on linearly polarized modes and mode coupling theory are in good agreement with our experiments and indicate that the decrease of coherence area is strongly related to a change in the modal amplitude distribution.

We present theoretical as well as experimental evidence of far-detuned nonlinear wavelength conversion towards the mid-infrared, namely beyond 3.5 μm, in a few-mode graded-index silica fiber pumped at 1.064 μm. We take into account the full frequency-dependence of the propagation constants, which allows us to obtain excellent agreement of theoretical predictions with experimental observations and provides new and accurate interpretation of intramodal and intermodal four-wave mixing processes in few-mode fibers.

We propose and demonstrate the concept of beam-by-beam cleaning in multimode optical fibres, i.e., the increase of the spatial quality of an intense laser beam, induced by a relatively weak, quasi singlemode seed beam. This effect, which relies on the Kerr nonlinearity of the fibre, is quite efficient: a seed beam is capable of providing a bell-shape to a ten times more powerful beam. Our results pave the way for the development of a new class of all-optical switching devices for intense laser beams.

Dual-comb molecular and pump-probe spectroscopy with equivalent time sampling are currently limited by the cost, complexity, and size of conventional optical comb systems, based on two modelocked lasers and corresponding feedback loops. The single-cavity dual-comb diode-pumped solid-state and semiconductor lasers, however, substantially reduce the complexity of existing systems to a single compact free-running laser. In comparison to other competing new approaches such as quantum cascade lasers or micro resonator combs, these dual-comb lasers provide substantially more power per comb line with low linewidth and noise, and are ideally suited for a 40 MHz to 5 GHz comb spacing. The optimal operating regime lies within this range for many different applications including spectroscopy and thin-film inspection, allowing for fast, accurate, and sensitive measurements.