We report an all-fiberized, dissipative-soliton, mode-locked thulium fiber laser enabled by a single-wall carbon nanotube saturable absorber operating at 1790 nm for deep-penetration three-photon microscopy in bio-medical imaging applications. The laser provides output pulses with a maximum pulse energy of 1.3 nJ and a minimum pulse duration of 310 fs after compression. With a new pump recycling design, a low pump threshold of 110 mW is observed. Consequently, a compact mode-locked thulium fiber laser cavity using a single-mode pump laser diode is successfully realized.

With the expanding utility of ultrafast sources for interferometric techniques like optical coherence tomography (OCT), we present a Dispersion Compensation Technique for Evident Chromatic Anomalies (DISCOTECA) as a universal solution to correct dispersion mismatch. We report a chromatic anomaly in the propagation of an ultrafast pulse through an interferometer beyond lower-order dispersions that worsens the axial resolution and causes image artifacts. We demonstrate the origin of these artifacts, explain our algorithm for the piecewise reconstruction and correction of the phase mismatch, and present a decision-making guide for interferometry with ultrashort sources. DISCOTECA corrects the artifacts from using ultrashort sources in OCT.

Deep tissue imaging remains challenging, especially for thick media, due to spherical aberrations induced on focused beams by the tissue. In this framework we propose a miniaturized in-vivo imaging window composed of high dioptric power microlenses coupled to micro-scaffold, which were fabricated by two-photon polymerization (2PP) in the biocompatible photoresist SZ2080. We adopt a single-irradiation strategy for the fabrication of the whole structure: We first irradiate the micro-scaffold on the bottom side of the chip and afterwards the microlenses on the top. For the microlenses we adopted a hybrid approach by combining the 2PP of the micro lenses surface with a subsequent UV crosslinking of the inner volume. We explored different lenses profiles (plano-convex and parabolic) with variable parameters like diameter and focal lengths, to optimize the imaging characteristics. We envisage that these imaging windows will open the way to direct and continuous optical inspection of biological processes in vivo.

Spatiotemporally precise control over complex biological processes in live cells is a long-sought-after goal for researchers. Currently, limited methodologies exist that have the chemical selectivity, spatial precision, or temporal response needed to image and manipulate dynamic biological processes simultaneously. We develop a novel technology, real-time precision opto-control (RPOC), that uses the optical signal generated during laser scanning imaging to activate lasers and control the chemical processes only at the desired pixel locations. We demonstrate the ability of RPOC to precisely manipulate cellular dynamics and as a versatile microsurgery platform for biological applications using a femtosecond laser source.

Reactive Oxygen Species (ROS) affect biological processes in many ways, and their effect is a function of strength, content and the exposure duration. Whereas excessive oxidative stress has potential to cause various deleterious events such as damaged protein structure, interfered activation of signaling cascades, and even cell apoptosis, we argue that targeted and carefully dosed application of ROS can be used as a therapeutic modality. In appropriate dosage ROS can induce stimulatory effects on cells and activate pathways leading to migration and collagen synthesis. At the tissue level ROS are utilized in photochemical crosslinking. Thus, we propose use of femtosecond oscillators as a therapeutic platform that can be utilized for ocular wound healing, non-invasive vision correction, as well as treatment of keratoconus and early osteoarthritis.

In a recent book chapter ^[1], we explored the conceptual feasibility of a room-temperature atom printer capable of constructing complex macroscopic objects with precise atomic control. We identified three challenges within current direct writing techniques and proposed a solution: integrating laser-driven self-organisation with direct writing. We assert that achieving absolute control over individual atoms may not be necessary; instead, harnessing internal feedback mechanisms that drive self-organisation could suffice. The crux is fine-tuning these feedback mechanisms to exert control over the atomic structure. This presentation will offer insight into our concept and showcase proof-of-concept demonstrations.

[1] S. Ilday und F. Ö. Ilday, „The universality of self-organisation: A path to an atom printer?“, in Ultrafast laser nanostructuring, Bd. 239, R. Stoian und J. Bonse, Hrsg. Cham: Springer International Publishing, 2023, S. 173–207. doi: 10.1007/978-3-031-14752-4_4.

We experimentally observe the broadband amplification of a seed laser pulse by at least 70x over its 500-1000nm range. The amplification was achieved by crossing a few-cycle seed pulse with a short 800 nm pump pulse at a near-90 degree angle, deviating from conventional plasma-based Raman amplifiers which employ near-parallel configurations. The amplification phenomenon occurred when the pump and seed pulses were crossed within an supersonic gas jet target.

We study the effects of controlled atmospheric turbulence on femtosecond filament-induced plasmas and ablation characteristics upon its interaction with solids at standoff distances. We evaluated shot-to-shot optical emission signal stability, electron number density, and plasma temperature as a function of turbulence strength. The surface topography of the ablation craters resulting from the filament-matter interaction was studied in detail and was correlated to the corresponding optical emission signals under different levels of turbulence. These findings provide first insights into filament-induced plasma optical emission signals and filament target-interaction under controlled turbulence conditions for remote elemental and isotopic sensing applications.

Nonlinear spectroscopy, such as sum-frequency generation spectroscopy and coherent Raman spectroscopy, are powerful tools for analyzing transient molecular structural changes. Achieving fast and high-resolution spectroscopy with these methods requires bandwidth compression techniques to convert broadband femtosecond pulses into synchronized narrowband picosecond pulses. Here we present a novel single-pass narrowband SHG method based on a novel pulse-shaping scheme using dispersion-engineered optical filters. In our first verification experiment, we found that the SHG bandwidth after passing the filter was compressed to 1/6, and the wavelength conversion efficiency was improved by 18 times compared to the case without the filter. This result demonstrates that precision-engineered optical filters can be used as a pulse-shaping tool. This alignment-free, single-pass bandwidth compression method may be an important tool for promoting the use of nonlinear spectroscopy in a wider range of fields.

Ultrafast laser based micro-processing has opened great opportunities to produce high-quality customized 3D glass devices. Thanks to the distinct advantages of ultrafast laser processing allowing minimized thermal effect and 3D freeform shaping, this technology has been widely used in glass device fabrication towards such applications requiring high optical transparency, biocompatibility, and chemical inactivity.

In this talk, I will demonstrate a few examples on fabrication of micro-structured glass chips for sensing and chemical reaction, exploiting femtosecond laser-based fabrication which includes selective laser etching and direct laser welding. In addition, I will discuss their characterization results and evaluation of device performance quantitatively. In-fiber microstructure for saturable absorber coated with conformal graphene will also be demonstrated and evaluated via ultrafast pulse generation.

Efficient and robust free-space light coupling in integrated systems is a challenging task for photonic devices. Here we propose a femtosecond laser process combined with CW laser thermal reflow for manufacturing a fiber-to-fiber free-space light-coupling device in fused silica. The monolithic free-space coupler design consists of two fiber holders and two ball lenses, used to achieve both, fiber-output collimation and fiber-injection. The device proved to efficiently work at 633 nm for single mode fiber coupling, which can be extended beyond the whole visible range with a simulated maximum efficiency of up to 90-95% of coupling.

Lately, the use of ultrafast in-volume laser-based processing of transparent materials has gained ground as a 3D-printing method of functional materials, photonics devices and high-density storage media. In this talk, we discuss the use of wide-field third-harmonic imaging that offers a non-destructive means for investigating and characterizing laser-written in-volume complex structures. Specifically, the method is used for identifying laser-induced modifications and establishing their taxonomy over a large area of a material. Unlike confocal arrangements, its ability to capture both the direct and scattered signal enables the collection of comprehensive information related to the local laser-induced modifications. Its inline nature allows for in situ monitoring of the material's response to various laser exposure conditions. As future prospect, it offers a pathway towards the implementation of closed-loop control algorithms, guaranteeing the accuracy and consistency of the desired modifications.

We report on recent research on the development of data-driven ultrashort pulse laser processing to achieve higher productivity and quality. We are developing in-process monitoring, artificial intelligence (AI) optimization, and fast active control of the laser based on them. These key technologies are introduced for micro-drilling of metals and transparent materials and laser-induced periodic surface structure (LIPSS) formation on a silica glass. We demonstrate a fast pulse-to-pulse modulation of the fluences to control the ablation efficiency. A deep neural network was utilized to predict the 3-dimensional shapes of the ablation craters depending on the laser parameters (fluence and pulse duration). The scheme was extended to 10 sequential modulations of fluences. An in-process monitoring of the crack formation on glasses was implemented by optical transmission imaging with deep neural network. The optical reflection/transmission technique was also employed to probe the quality of the LIPSS formation on a silica glass.

Among recent advanced manufacturing techniques introduced over the last decades, non-ablative femtosecond laser processing has gained a lot of attention thanks to its applicability to a variety of substrates and its unique ability to locally process transparent materials in their volumes. The laser-induced taxonomy of structural modifications is rich and, despite the extreme brevity of the laser-matter interaction, includes nano-crystallization events as recently reported in various amorphous substrates. Yet, the mechanism leading to these nano-crystallization phenomena driven by locally extreme exposure conditions, similar to warm-dense state of matter (WDM), remains elusive.

We present in situ nano-crystallization dynamics using X-ray microdiffraction, reporting such experiments for the first time to our knowledge. Specifically, we investigate the case of a femtosecond laser-induced nano-crystallization process in an amorphous multilayer stack of Al₂O₃/Nb₂O₅ layers using operando X-ray micro-diffraction at the microXAS beamline of the Swiss Light Source (SLS). We identify the crystalline phases and the timescales of the transition using varying laser exposure conditions.

We report on the experimental demonstration of enhanced-frequency-chirping (EFC) in a multipass cell (MPC) based post-compression scheme through dispersion engineering. The transfer of the nonlinear interaction into the EFC-regime facilitates a smooth spectrum void of strong modulations that are present in regular self-phase-modulated spectra. The resulting 32 fs pulses exhibit minimal side features with more than 96% of energy contained in the temporal main feature. The experiments were performed with a mJ-class Yb:fiber laser with repetition rate of 50kHz at 70 W of average power. The results show the extended capabilities for dispersion-tailored pulse propagation in MPCs.

Gas-filled hollow core fibers are a promising and unique platform for generation of ultrafast and wavelength tunable UV light. We present recent advances from our lab focused towards two vastly different industrial applications: Laser processing of solar cells and scatterometry. For processing of solar cells, we use the intrinsic wavelength tuning ability to investigate the potential for selective ablation and wire bonding. For scatterometry, which requires a broadband, flat, and low noise spectrum, we use pump modulation to create a pseudo-supercontinuum.

We report on power scaling of Yb-doped femtosecond lasers emitting at 1030 nm with multi-mJ pulse energies from the level of several 100-W of average output power to a level exceeding 1 kW. Technological building blocks that are crucial for scaling power and pulse energy will be presented. Additionally, we highlight functionalities that have been developed and integrated into the high-power femtosecond laser systems to optimally exploit their potential in different relevant use cases for industrial applications. Moreover, the perspectives for further power and pulse energy scaling will be discussed.

Stabilizing the electric field in few cycle ultrashort laser pulses is necessary for performing many experiments in the attosecond time regime and for generating High-Harmonics (HHG). Traditional CEP methods are based on measuring the carrier envelope offset frequency and using an external feedback mechanism (pump power, intracavity dispersion, etc.) to stabilize the phase in femtosecond oscillators and amplifiers. In this talk, a novel feed-forward method for stabilizing a <25 fs, mJ-level regenerative amplifier is presented. Using this patented technique, <100 mrad (10-shot average) and <300 mrad single-shot noise performance was demonstrated for more than 150 hours. Details of this novel feed-forward approach will be discussed, and the results compared to other currently available methods.

Ultrafast Laser Inscription enables the fabrication of arbitrary 3-dimensional optical waveguides in optical glass. The use of material science and glass chemistry has facilitated the creation of substrate materials with properties tailored to Ultrafast Laser Inscription to reach sub-decibel end-to-end insertion losses. Using these 3D waveguide circuits to interface with multicore, few-mode and few-mode multicore fibers has seen the demonstration of record-breaking data rates for space-division-multiplexed optical communication.

We introduce a high-harmonic generation (HHG)-based XUV source that offers a broad photon flux range from 40 eV to 150 eV. This source utilizes an industrial-grade TruMicro 2030 laser system with 20-W average power, delivering up to 100 µJ with pulse durations under 400 fs. A post-compression unit is incorporated to reduce the pulses to approximately 40 fs with just a 10% average power loss. The turnkey source achieves a photon flux exceeding 10^10 photons/s around 70 eV.

Menhir Photonics’ robust and reliable ultra low-noise ultrafast seeders are now a reference at 1.5 um. At 1030 nm, we present a flexible concept using our new MENHIR-1030 at 160 MHz together with nearly lossless resonant EOM pulse-picking to serve as ultra-low noise seeder for amplifier systems requiring 80 MHz or 40 MHz repetition rate. We provide >1 nJ of pulse energy while maintaining the high robustness and compactness of a high repetition rate system, combined with state-of-the art low jitter. The passively stable MENHIR-1030 can be actively stabilized for utmost stability in amplifier applications. We will review the laser's key parameters with our innovative concept and details on key applications from our customers such as enhancement cavity pumping and high-power amplification.

The study and control of hypersonic air flow over a geometry or surface is an area of interest in aerodynamic engineering. Previous studies on drag reduction have utilised effects from short pulse lasers, however, the investigation of high energy ultrafast laser pulse deposition in hypersonic flow poses challenges from laser and wind tunnel requirements, and their integration. We present the novel application of an ultrafast Ti:Sapphire laser delivering pulses of 62 fs duration at energies up to 44 mJ on a 7° axisymmetric cone model in Mach 7.0 flow. We discuss laser-facility integration, optical and engineering challenges, and experimental results of parameterised characterisation of flow modification.