Enhanced recovery after surgery is feasible and safe in liver transplantation: a cohort study.

BACKGROUND: The principles of enhanced recovery after surgery (ERAS) are being applied to still more advanced procedures. Liver transplantation offers a unique opportunity for a multimodal approach including donor care as well. Our objective was to determine if ERAS was applicable and safe in orthotopic liver transplantation (OLT). METHODS: A national single centre retrospective study showing the implementation of ERAS from 2013 to 2019 with the proceeding 2 years serving as baseline. The primary endpoints were mortality, length of stay (LOS) in the ward and intensive care unit stay. Secondary endpoints were complications estimated by Dindo-Clavien classification, comprehensive complication index (CCI®) and re-admissions. RESULTS: A total of 334 patients were included. LOS was significantly reduced from a median of 22.5 days at introduction to 14 days at 2019. Cold ischaemia time was reduced from a mean of 10.7 to 6.0 h and the use of blood products (erythrocytes, plasma and thrombocytes) from a median of 28 to 6 units. Complications were reduced in severity. Mortality and readmission rates were not affected. CONCLUSION: ERAS principles are safe and recommended in patients undergoing OLT resulting in reduced severity of complications and LOS without affecting re-admissions or mortality.

High-resolution mid-infrared optical coherence tomography with kHz line rate.

We report on mid-infrared optical coherence tomography (OCT) at 4 µm based on collinear sum-frequency upconversion and promote the A-scan scan rate to 3 kHz. We demonstrate the increased imaging speed for two spectral realizations, one providing an axial resolution of 8.6 µm, and one providing a record axial resolution of 5.8 µm. Image performance is evaluated by sub-surface micro-mapping of a plastic glove and real-time monitoring of CO2 in parallel with OCT imaging.

Thermally tunable dispersion modulation in a chalcogenide-based hybrid optical fiber.

A hybrid optical fiber comprising metal electrodes, high performance polymers, and a highly nonlinear glass core is presented in this work as a novel, to the best of our knowledge, platform for mid-infrared nonlinear devices. The fiber allows for electrical tuning of the temperature by joule heating using a set of embedded tungsten wires. Unlike temperature tuning by an external heater, this results in a strong modulation, which introduces alternating signs of its dispersion. Enhanced spectral broadening through supercontinuum generation in the mid-infrared due to this modulation is investigated numerically.

Power stable 1.5-10.5 µm cascaded mid-infrared supercontinuum laser without thulium amplifier.

We demonstrate a simple and power stable 1.5-10.5 µm cascaded mid-infrared 3 MHz supercontinuum fiber laser. To increase simplicity and decrease cost, the design of the fiber cascade is optimized so that no thulium amplifier is needed. Despite the simple design with no thulium amplifier, we demonstrate a high average output power of 86.6 mW. Stability measurements for seven days with 8-9 h operation daily revealed fluctuations in the average power with a standard deviation of only 0.43% and a power spectral density stability of ±0.18dBm/nm for wavelengths <10µm. The high-repetition-rate, robust, and cheap all-fiber design makes this source ideal for applications in spectroscopy and imaging.

Influence of pulse duration and repetition rate on mid-infrared cascaded supercontinuum.

We experimentally investigate the influence of varying pulse parameters on the spectral broadening, power spectral density, and relative intensity noise of mid-infrared (mid-IR) in-amplifier cascaded supercontinuum generation (SCG) by varying the pulse duration (35 ps, 1 ns, 3 ns) and repetition rate (100, 500, 1000 kHz). The system is characterized at the output of the erbium-ytterbium-doped in-amplifier SCG stage, the thulium/germanium power redistribution stage, and the passive ZBLAN fiber stage. In doing so, we demonstrate that the output of the later stages depends critically on the in-amplifier stage, and relate this to the onset of modulation instability.

In-amplifier and cascaded mid-infrared supercontinuum sources with low noise through gain-induced soliton spectral alignment.

The pulse-to-pulse relative intensity noise (RIN) of near-infrared (near-IR) in-amplifier supercontinuum (SC) sources and mid-IR cascaded SC sources was experimentally and numerically investigated and shown to have significantly lowered noise due to the fundamental effect of gain-induced soliton-spectral alignment. The mid-IR SC source is based on a near-IR in-amplifier SC pumping a cascade of thulium-doped and ZBLAN fibers. We demonstrate that the active thulium-doped fiber not only extend the spectrum, but also to significantly reduce the RIN by up to 22% in the long wavelength region above 2 µm. Using numerical simulations, we demonstrate that the noise reduction is the result of an interplay between absorption-emission processes and nonlinear soliton dynamics leading to the soliton-spectral alignment. In the same way we show that the RIN of the near-IR in-amplifier SC source is already significantly reduced because the spectral broadening takes place in an active fiber that also introduces soliton-spectral alignment. We further show that the low noise properties are transferred to the subsequent fluoride SC, which has a RIN lower than 10% (5%) in a broad region from 1.1-3.6 µm (1.4-3.0 µm). The demonstrated low noise significantly improves the applicability of these broadband sources for mid-IR imaging and spectroscopy.

All-fibre supercontinuum laser for in vivo multispectral photoacoustic microscopy of lipids in the extended near-infrared region.

Among the numerous endogenous biological molecules, information on lipids is highly coveted for understanding both aspects of developmental biology and research in fatal chronic diseases. Due to the pronounced absorption features of lipids in the extended near-infrared region (1650-1850 nm), visualisation and identification of lipids become possible using multi-spectral photoacoustic (optoacoustic) microscopy. However, the spectroscopic studies in this spectral region require lasers that can produce high pulse energies over a broad spectral bandwidth to efficiently excite strong photoacoustic signals. The most well-known laser sources capable of satisfying the multi-spectral photoacoustic microscopy requirements (tunability and pulse energy) are tunable nanosecond optical parametric oscillators. However, these lasers have an inherently large footprint, thus preventing their use in compact microscopy systems. Besides, they exhibit low-repetition rates. Here, we demonstrate a compact all-fibre, high pulse energy supercontinuum laser that covers a spectral range from 1440 to 1870 nm with a 7 ns pulse duration and total energy of 18.3 µJ at a repetition rate of 100 kHz. Using the developed high-pulse energy source, we perform multi-spectral photoacoustic microscopy imaging of lipids, both ex vivo on adipose tissue and in vivo to study the development of Xenopus laevis tadpoles, using six different excitation bands over the first overtone transition of C-H vibration bonds (1650-1850 nm).

Nanoimprinting and tapering of chalcogenide photonic crystal fibers for cascaded supercontinuum generation.

Improved long-wavelength transmission and supercontinuum (SC) generation is demonstrated by antireflective (AR) nanoimprinting and tapering of chalcogenide photonic crystal fibers (PCFs). Using a SC source input spanning from 1 to 4.2 µm, the total transmission of a 15 µm core diameter PCF was improved from ∼53% to ∼74% by nanoimprinting of AR structures on both input and output facets of the fiber. Through a combined effect of reduced reflection and redshifting of the spectrum to 5 µm, the relative transmission of light >3.5 µm in the same fiber was increased by 60.2%. Further extension of the spectrum to 8 µm was achieved using tapered fibers. The spectral broadening dynamics and output power were investigated using different taper parameters and pulse repetition rates.

Deep-UV to Mid-IR Supercontinuum Generation driven by Mid-IR Ultrashort Pulses in a Gas-filled Hollow-core Fiber.

Supercontinuum (SC) generation based on ultrashort pulse compression constitutes one of the most promising technologies towards ultra-wide bandwidth, high-brightness, and spatially coherent light sources for applications such as spectroscopy and microscopy. Here, multi-octave SC generation in a gas-filled hollow-core antiresonant fiber (HC-ARF) is reported spanning from 200 nm in the deep ultraviolet (DUV) to 4000 nm in the mid-infrared (mid-IR) having an output energy of 5 µJ. This was obtained by pumping at the center wavelength of the first anti-resonant transmission window (2460 nm) with ~100 fs pulses and an injected pulse energy of ~8 µJ. The mechanism behind the extreme spectral broadening relies upon intense soliton-plasma nonlinear dynamics which leads to efficient soliton self-compression and phase-matched dispersive wave (DW) emission in the DUV region. The strongest DW is observed at 275 nm which corresponds to the calculated phase-matching wavelength of the pump. Furthermore, the effect of changing the pump pulse energy and gas pressure on the nonlinear dynamics and their direct impact on SC generation was investigated. This work represents another step towards gas-filled fiber-based coherent sources, which is set to have a major impact on applications spanning from DUV to mid-IR.

Real-time high-resolution mid-infrared optical coherence tomography.

The potential for improving the penetration depth of optical coherence tomography systems by using light sources with longer wavelengths has been known since the inception of the technique in the early 1990s. Nevertheless, the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region, resulting in slow acquisition, low sensitivity, and poor axial resolution. In this work, a mid-infrared spectral-domain optical coherence tomography system operating at a central wavelength of 4 µm and an axial resolution of 8.6 µm is demonstrated. The system produces two-dimensional cross-sectional images in real time enabled by a high-brightness 0.9- to 4.7-µm mid-infrared supercontinuum source with a pulse repetition rate of 1 MHz for illumination and broadband upconversion of more than 1-µm bandwidth from 3.58-4.63 µm to 820-865 nm, where a standard 800-nm spectrometer can be used for fast detection. The images produced by the mid-infrared system are compared with those delivered by a state-of-the-art ultra-high-resolution near-infrared optical coherence tomography system operating at 1.3 µm, and the potential applications and samples suited for this technology are discussed. In doing so, the first practical mid-infrared optical coherence tomography system is demonstrated, with immediate applications in real-time non-destructive testing for the inspection of defects and thickness measurements in samples that exhibit strong scattering at shorter wavelengths.

High-pulse energy supercontinuum laser for high-resolution spectroscopic photoacoustic imaging of lipids in the 1650-1850 nm region.

We propose a cost-effective high-pulse energy supercontinuum (SC) source based on a telecom range diode laser-based amplifier and a few meters of standard single-mode optical fiber, with a pulse energy density as high as ~25 nJ/nm in the 1650-1850 nm regime (factor >3 times higher than any SC source ever used in this wavelength range). We demonstrate how such an SC source combined with a tunable filter allows high-resolution spectroscopic photoacoustic imaging and the spectroscopy of lipids in the first overtone transition band of C-H bonds (1650-1850 nm). We show the successful discrimination of two different lipids (cholesterol and lipid in adipose tissue) and the photoacoustic cross-sectional scan of lipid-rich adipose tissue at three different locations. The proposed high-pulse energy SC laser paves a new direction towards compact, broadband and cost-effective source for spectroscopic photoacoustic imaging.

Refractive index and dispersion control of ultrafast laser inscribed waveguides in gallium lanthanum sulphide for near and mid-infrared applications.

The powerful ultrafast laser inscription technique is used to fabricate optical waveguides in gallium lanthanum sulphide substrates. For the first time the refractive index profile and the dispersion of such ultrafast laser inscribed waveguides are experimentally measured. In addition the Zero Dispersion Wavelength of both the waveguides and bulk substrate is experimentally determined. The Zero Dispersion Wavelength was determined to be between 3.66 and 3.71 µm for the waveguides and about 3.61 µm for the bulk. This work paves the way for realizing ultrafast laser inscribed waveguide devices in gallium lanthanum sulphide glasses for near and mid-IR applications.

Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber.

A low-loss suspended core As(38)Se(62) fiber with core diameter of 4.5 µm and a zero-dispersion wavelength of 3.5 µm was used for mid-infrared supercontinuum generation. The dispersion of the fiber was measured from 2.9 to 4.2 µm and was in good correspondence with the calculated dispersion. An optical parametric amplifier delivering 320 fs pulses with a peak power of 14.8 kW at a repetition rate of 21 MHz was used to pump 18 cm of suspended core fiber at different wavelengths from 3.3 to 4.7 µm. By pumping at 4.4 µm with a peak power of 5.2 kW coupled to the fiber a supercontinuum spanning from 1.7 to 7.5 µm with an average output power of 15.6 mW and an average power >5.0 µm of 4.7 mW was obtained.