This PDF file contains the front matter associated with SPIE Proceedings Volume 11991, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Femtosecond laser processing is well known because of the achievable unparalleled precision with minimized thermal effects on most materials, making this technology competitive for its clinical use on living tissue. Nevertheless, femtosecond laser processing often requires an optimization of the parameters in order to increase the ablation rate which remains too limited compared to CW or QCW lasers. This study identifies an optimized set of process parameters (wavelength, temperature, bone hydration) for efficiently ablating bone tissue. Three different absorption regimes are studied using fs laser sources centered at wavelengths of 1030 nm, 515 nm and 343 nm. The thermal effects generated by the interaction of the fs laser and the bone were analyzed using a thermal camera and thermocouples with different cooling methods (water and air). Our results highlight (i) the significant capacity of the visible wavelength (515 nm) to ablate bone tissue with a maximum value of 0.66 mm³/s on pork femurs and that (ii) the use of water for cooling the sample is the most effective method of cooling and reduce thermal propagation without impacting the ablation rate. This study also raises awareness about the role of the anatomical region (femur, tibia, etc.) and species (pig, chicken, etc.) of the investigated bone tissue samples which may induce significant differences in ablation efficiency.

Ultrashort pulsed lasers are being increasingly used for high precision micromachining across many industries. To further optimise these processes, consideration of the spatial profile of the laser beam is essential, as the shape of the processed area often closely resembles the intensity distribution used. Within surgical contexts, ultrashort infrared pulsed lasers offer significantly improved localisation in the ablation of biological tissues over current electrocautery methods through their non-contact, plasma-mediated interaction mechanisms. This localisation can reduce the risk of severe complications such as bowel perforation. However, for incorporation into an endoscopic device, the limited focal depths inherent to tightly focused Gaussian beams can greatly hinder the ablation of inhomogeneous tissue surfaces. However, alternative beam shapes, such as Bessel-Gauss beams, enable a decoupling of the focal volume from the focal depth. Various beam profiles and laser scanning parameters have been investigated, capitalising upon the distinct advantages offered from applying ultrashort pulsed lasers to microsurgery of tissue. Assessment of the corresponding ablation profiles in porcine intestinal tissue was performed through both three-dimensional optical surface profilometry and histological analysis. Using a Bessel-Gauss beam, ablated depths close to a millimetre were achieved while showcasing peak thermal damage margins of around 30 µm. If adopted in operating theatres, surgeons could benefit from increased precision when resecting neoplasia in the mucosal and submucosal layers of the colon, providing them with greater levels of control both in terms of lateral accuracy and in moderating the depth of tissue removed, especially when compared to current electrocautery methods.

Multiphoton microscopy is regularly used to produce high-resolution images of in vivo neural structure, but strategies to increase both the imaging depth and field of view are needed. To aid with deep imaging, we present an ultrafast laser system consisting of a custom ytterbium fiber amplifier and diamond Raman laser that output high powers (6.5 W, 1.3 W) at valuable wavelengths (1060 nm, 1250 nm) for multiphoton excitation of red-shifted fluorophores. The entire system is relatively inexpensive and simple to construct as compared to alternative custom and commercial excitation options. The 80 MHz repetition rate of each laser in the system is also notable, as it allows a resonant scanner to be used for imaging to dramatically increase acquisition rate. In this work we demonstrate the ability to acquire neuronal images, and the capability to image vasculature at deep locations (<1 mm) within the mouse cerebral cortex. We also present a strategy to image over a large field of view involving a resonant scanner and make use of this to monitor neurovascular structure longitudinally within a volume of one cubic millimeter.

Integrated optical switches and modulators allow performing reconfigurability in integrated circuits, resulting as fundamental components in different fields ranging from optical communications to sensing and metrology. Among different methods, the thermo-optic effect has been successfully used to fabricate optical modulators by femtosecond laser micromachining (FLM) in glass substrates, proving high stability, no losses dependance but long switching time. In this work, we present an integrated optical switch realized by FLM with a switching time of less than 1 ms: which is about 1 order of magnitude faster than the other devices present in literature. This result has been achieved by carefully optimizing the geometry and the position of resistors and trenches near the waveguides through simulation and experimental validation. In addition, by means of an optimization of the applied voltage signal, we have demonstrated a further significant temporal improvement, measuring a switching time of less than 100 μs.

In recent years, quantum cascade lasers have matured to become compact, powerful sources of coherent midinfrared light. Yet, the ultrafast carrier dynamics in these sources has so far restricted the formation of highintensity ultrashort pulses. In this work, we demonstrate the formation of ∼ 630 fs QCL pulses with a peak power of ∼ 4.3 W. We break the picosecond barrier in an approach similar to chirped pulse amplification, where we externally recompress the maximally chirped output of a quantum cascade laser frequency comb. Ultrashort pulse formation is confirmed with a novel asynchronous optical sampling technique. These results emphasise the potential of quantum cascade lasers also as sources for non-linear experiments in the mid-infrared.

We report on the separation of glass substrates with customized edge contours including C-shapes. To achieve single-pass laser modifications along the entire contour geometry a processing optics is presented where a multitude of foci are simultaneously distributed inside a specific volume using a large-working-volume focusing unit. Tangential angles of the focus trajectory to the surface can be almost arbitrarily chosen and amount to even less than 45-deg in case of aiming for chamfered edges. After having induced laser modifications along the desired edge geometry, separation is done chemically in the present case. The glass articles, thus fabricated, meet the demands of the display industry in terms of bending strength and surface quality.

We report on the design and realization of novel non-diffracting beams for ultrashort laser materials processing. Our method is axicon based and introduces subtle azimuthal modifications to the conical lenses or well-defined misalignments to achieve a set of novel non-diffracting beams. These focus distributions retain all well-known advantages of non-diffracting beams, such as self-healing, high optical efficiency, or possible extreme aspect ratios. Additionally, tailored transverse intensity profiles with, for example, well-defined preferential direction can be generated. Clear advantages for controlling residual stress and crack orientation in glass processing are discussed and results of different micro-machining experiments are presented.

There are significant advantages for on-board and co-packaged optics in next-generation data centers. However, the highvolume manufacturing of the photonic circuits that underpin the technology will require the fabrication of large quantities on a wafer- or panel-scale, which must then be singulated into individual devices. A major challenge is the requirement for low-loss edge coupling to optical fibers (optical-quality and vertical end-facets) which typically requires expensive and time-consuming post-processing steps such as mechanical polishing. In this work, an ultrafast laser is employed to singulate glass substrates using a non-diffracting beam that creates a localized material modification through the entire glass thickness via nonlinear laser-material interactions. By controlling the placement of the laser modifications, the regions around the waveguides could be strategically avoided. This leaves optical-quality regions around the waveguides which provide the same low-loss edge coupling as the polished end-facets. This process can be applied to optical circuits containing planar ion-exchanged waveguides and 3D ultrafast laser-inscribed waveguides in the bulk glass without the need for post-polishing the end-facet and thus opens the opportunity for more rapid device prototyping and lower-cost high-volume manufacturing.

Ultrashort optical pulses find uses in many areas such as multiphoton microscopy, spectroscopy, and material processing. These pulse sources are complex systems that are resource-intensive. This necessitates methods for the robust delivery of pulses to time-varying satellite locations. Characterization of the power spectrum and the temporal profile of the delivered pulses without the need for specialized equipment at the satellite location is highly desirable. Here, we demonstrate a simple method using a compact measurement apparatus at satellite locations with power detectors at the fundamental and second harmonic wavelengths (Germanium and Silicon detectors, respectively). The module also includes a thin β-Barium Borate crystal for second harmonic generation and a communication link to the source using standard data protocols. A pulse shaper at the source emulates an interferometer by creating pulse pairs with varying time delays. At satellite locations, fundamental and SHG power measurements of the pulse pair provide the field autocorrelation function (Fourier transform of the power spectrum) and the intensity autocorrelation function, respectively. Transform-limited pulses can be delivered by compensating the measured dispersion dynamically using the pulse shaper. We have delivered sub-picosecond pulses from a C-band mode-locked fiber laser with a bandwidth of 20nm over 50 and 100m using existing telecom fiber links. The pulse widths and spectra obtained using the remote measurement matched with those made directly at the satellite location. This provides easy distribution and remote characterization for femtosecond lasers from a central location to various satellite locations.

Optical coherence tomography (OCT) is a high-resolution and non-invasive internal structural imaging technique. Since the first introduction of OCT, it has been widely studied to enhance the scanning speed of the system to enhance the applicability. Spectral-domain OCT (SD-OCT) is one of the representative types of Fourier-domain OCT, which consisted with lower prices than swept-source OCT and offers higher axial resolution, but there are limited hardware performance to improve the scanning speed. In this paper, we introduced the space-time division multiplexing (STDM) method-based superfast SD-OCT with 1 MHz A-scan rate. In terms of the time-division method, dual-cameras were implemented in a single spectrometer to reduce the alignment error between each camera and fully utilize the operating time of camera by remove the dead time. In addition, the path length difference of the two-sample arm is accurately controlled to utilize the space-division method. By concurrently integrating the time- and space-division methods in STDM with GPU parallel computing, 32 volume/sec was acquired. The quantitative evaluation of the performance of STDM-OCT was analyzed with sensitivity roll-off and image quality comparison measured at different depth. The proposed STDM-OCT is able to enlarge the application of OCT including biomedical research areas, which require a high-speed scanning system.