100 W, tunable in-band thulium fiber amplifier pumped by incoherently combined 1.9 µm fiber lasers.

We detail the design and performance of a high efficiency in-band pumped thulium fiber amplifier operating at the 100 W level. Using a novel pumping architecture based on three incoherently combined thulium fiber oscillators at 1904 nm and a seed laser tunable from 1970-1990 nm, efficient amplification is demonstrated in a high dopant concentration 25/65/250 µm thulium fiber. Here we use the 65 µm pedestal surrounding the core as a pump cladding to increase the cladding to core overlap and improve the overall pump absorption. Up to 89% slope efficiency is obtained with ∼100 W output power at 1990 nm. These results indicate that in-band pumping is a viable route to circumvent the thermal limitations associated with 793 nm diode pumping and provide a pathway for development of multi-kW laser sources in the 2 µm spectral window.

Single-centre review of the management of intra-thoracic oesophageal perforation in a tertiary oesophageal unit: paradigm shift, short- and long-term outcomes over 15 years.

BACKGROUND: Oesophageal perforation is an uncommon surgical emergency associated with high morbidity and mortality. The timing and type of intervention is crucial and there has been a major paradigm shift towards minimal invasive management over the last 15 years. Herein, we review our management of spontaneous and iatrogenic oesophageal perforations and assess the short- and long-term outcomes. METHODS: We performed a retrospective review of consecutive patients presenting with intra-thoracic oesophageal perforation between January 2004 and Dec 2020 in a single tertiary hospital. RESULTS: Seventy-four patients were identified with oesophageal perforations: 58.1% were male; mean age of 68.28 ± 13.67 years. Aetiology was spontaneous in 42 (56.76%), iatrogenic in 29 (39.2%) and foreign body ingestion/related to trauma in 3 (4.1%). The diagnosis was delayed in 29 (39.2%) cases for longer than 24 h. There was change in the primary diagnostic modality over the period of this study with CT being used for diagnosis for 19 of 20 patients (95%). Initial management of the oesophageal perforation included a surgical intervention in 34 [45.9%; primary closure in 28 (37.8%), resection in 6 (8.1%)], endoscopic stenting in 18 (24.3%) and conservative management in 22 (29.7%) patients. On multivariate analysis, there was an effect of pathology (malignant vs. benign; p = 0.003) and surgical treatment as first line (p = 0.048) on 90-day mortality. However, at 1-year and overall follow-up, time to presentation (≤ 24 h vs. > 24 h) remained the only significant variable (p = 0.017 & p = 0.02, respectively). CONCLUSION: Oesophageal perforation remains a condition with high mortality. The paradigm shift in our tertiary unit suggests the more liberal use of CT to establish an earlier diagnosis and a higher rate of oesophageal stenting as a primary management option for iatrogenic perforations. Time to diagnosis and management continues to be the most critical variable in the overall outcome.

Numerical simulation of steady-state thermal blooming with natural convection.

This work investigates steady-state thermal blooming of a high-energy laser in the presence of laser-driven convection. While thermal blooming has historically been simulated with prescribed fluid velocities, the model introduced here solves for the fluid dynamics along the propagation path using a Boussinesq approximation to the incompressible Navier-Stokes equations. The resultant temperature fluctuations were coupled to refractive index fluctuations, and the beam propagation was modeled using the paraxial wave equation. Fixed-point methods were used to solve the fluid equations as well as to couple the beam propagation to the steady-state flow. The simulated results are discussed relative to recent experimental thermal blooming results [Opt. Laser Technol.146, 107568 (2022) OLTCAS0030-399210.1016/j.optlastec.2021.107568], with half-moon irradiance patterns matching for a laser wavelength at moderate absorption. Higher energy lasers were simulated within an atmospheric transmission window, with the laser irradiance exhibiting crescent profiles.

Tackling a Post-COVID-19 Cholecystectomy Waiting List: Are We Meeting the Challenge?

Background and Objectives: The COVID-19 pandemic has led to a tremendous backlog in elective surgical activity. Our hospital trust adopted an innovative approach to dealing with elective waiting times for cholecystectomy during the recovery phase from COVID-19. This study aimed to evaluate trends in overall cholecystectomy activity and the effect on waiting times. Materials and Methods: A prospective observational study was undertaken, investigating patients who received a cholecystectomy at a large United Kingdom hospital trust between February 2021 and February 2022. There were multiple phased strategies to tackle a 533-patient waiting list: private sector, multiple sites including emergency operating, mobile theatre, and seven-day working. The correlation of determination (R2) and Kruskal-Wallis analysis were used to evaluate trends in waiting times across the study period. Results: A total of 657 patients underwent a cholecystectomy. The median age was 49 years, 602 (91.6%) patients had an ASA of 1-2, and 494 (75.2%) were female. A total of 30 (4.6%) patients were listed due to gallstone pancreatitis, 380 (57.8%) for symptomatic cholelithiasis, and 228 (34.7%) for calculous cholecystitis. Median waiting times were reduced from 428 days (IQR 373-508) to 49 days (IQR 34-96), R2 = 0.654, p < 0.001. For pancreatitis specifically, waiting times had decreased from a median of 218 days (IQR 139-239) to 28 (IQR 24-40), R2 = 0.613, p < 0.001. Conclusions: This study demonstrates the methodology utilised to safely and effectively tackle the cholecystectomy waiting list locally. The approach utilised here has potential to be adapted to other units or similar operation types in order to reduce elective waiting times.

Sonic anemometer data processing for comparison to optical turbulence theory and simulation.

With appropriate processing techniques, sonic anemometry can provide useful insights into the strength and spectral shape of optical turbulence. Closed form propagation models and simulations require stationary optical turbulence statistics to make a meaningful comparison with experimental results. This work presents a new approach for examining the stationarity of data provided by sonic anemometry and by fitting optical turbulence parameters. Von Kármán, Greenwood-Tarazano, and one minus exponential spectral models are fitted to experimental data. Each model fit is evaluated using information criteria. The Greenwood-Tarazano model is shown to provide the best fit to experimental data. Optical turbulence parameters from the Greenwood-Tarazano model are compared with results from instruments at varying heights above the ground.

Laser-plasma coupling for enhanced ablation of GaAs with combined femtosecond and nanosecond pulses.

The laser-plasma interactions that occur during the ablation of solid materials by a femtosecond filament superimposed with a lower-intensity nanosecond pulse are investigated. Pulses of 50 fs duration with intensities of ∼1014 W/cm2 centered at 800 nm are combined with 8 ns pulses at 1064 nm with ∼1010 W/cm2 intensity with delays of ±40 ns on crystalline GaAs targets in air. For each delay, the volume of material removed by a single femtosecond-nanosecond dual-pulse is compared to the laser-plasma interactions that are captured with ultrafast shadowgraph imaging of the plasma and shockwave generated by each pulse. Sedov-Taylor analysis of the shockwaves provides insight on the coupling of energy from the second pulse to the plasma. These dynamics are corroborated with radiation-hydrodynamics simulations. The interaction of the secondary pulse with the pre-existent plasma is shown to play a critical role in enhancing the material removal.

Filament conductivity enhancement through nonlinear beam interaction.

Laser filament applications relying on filament plasma conductivity are limited by their low electron densities and corresponding short lifetimes. Filament plasma formation, an intensity-dependent process, is limited by the clamping of the filament core intensity. Consequently, increasing initial beam energy results in the breakup of the beam into multiple filaments rather than the enhancement of the electron density and conductivity of an individual filament. However, we demonstrate here the augmentation of the filament plasma density up to three times the typical value through the energy exchange between two co-propagating femtosecond beams with total powers between 1.7 and 2.2 Pfil.

Stereotactic Body Radiation Therapy (SBRT) in Pelvic Lymph Node Oligometastases.

The role of stereotactic body radiation therapy (SBRT) in achieving durable local control and palliation of pain in pelvic lymph node oligometastatic disease is not well-studied. We performed a retrospective analysis of 30 patients with 43 pelvic lymph node oligometastases from various primary cancers all but one with non-prostate primaries treated at our institution with SBRT. The median follow-up time was 21 months. The median SBRT dose was 24 Gy in four fractions. The one-, two-, and five-year local control was 74%, 71%, and 70% and one-, two-, and five-year overall survival was 70%, 47%, and 31%. Toxicities were mild with no grade 3 or higher.

Stereotactic body radiation therapy (SBRT) in recurrent, persistent or oligometastatic gynecological cancers.

OBJECTIVE: SBRT is a well-tolerated technique and provides local-regional control in a variety of metastatic and recurrent tumor types. The role of SBRT in extracranial recurrent, persistent, or oligometastatic gynecological tumors is not well-studied. We therefore retrospectively analyzed a sizeable number of patients in this setting. METHODS: We performed a retrospective review of 86 patients with 209 tumors treated at our institution with SBRT for recurrent, persistent, or oligometastatic extracranial gynecological tumors. The median follow-up was 20 months (range 1-91). The median SBRT dose was 24 Gy (range 10-50) delivered in a median of 4 fractions (range 1-6). The Kaplan-Meier curves and log rank tests were used to assess local control (LC) and overall survival (OS). Cox proportional hazards model was used to evaluate for covariates associated with LC and OS. RESULTS: The 1- and 3-year LC were 80% and 68% respectively. The 1- and 3-year OS were 70% and 39%. 32% of the lesions demonstrated complete response, 23% partial response and 20% stable disease. SBRT achieved better local control in smaller tumors. Toxicity was typically mild with grade 1 gastrointestinal toxicity and fatigue being the most common. Only 4.3% of treatments resulted in grade 2 or greater toxicity. There was only one case of grade 3 and no grade 4 or 5 toxicities. CONCLUSIONS: SBRT offers a high rate of local control with low incidence of toxicity, mainly grade 1 GI toxicity and fatigue, and provides effective salvage therapy for oligometastatic extracranial pelvic and extra-pelvic gynecological tumors.

Direct wavefront measurements of filaments in the assisted-collapse regime.

Wavefront measurements are used to characterize the process of filament formation in air under assisted-collapse conditions. Direct wavefront evolution within the filament, measured for the first time, is used to characterize the role of energy reservoir in filament formation. This information provides new insights into the filament process and phase sensitive applications such as engineered plasma waveguides.

Efficient coupling of a quantum cascade laser to a few-mode chalcogenide fiber: erratum.

The authors wish to acknowledge an additional funding source which was absent from our manuscript.

Efficient coupling of a quantum cascade laser to a few-mode chalcogenide fiber.

We report efficient coupling of a quantum cascade laser (QCL) into step-index chalcogenide fibers (As 2S 3). Mechanically robust and low-loss chalcogenide fibers were fabricated using a hybrid, multi-material thermal drawing process. With suitable free-space optics, more than 160 mW of optical power was coupled into the fiber with predominantly single-mode excitation. Antireflection coatings on the fiber facets enabled 88.9% transmission with strong core confinement. By accurately tailoring the core diameter and antireflection-coating thickness, these fibers offer a versatile platform for high-power and low-loss transmission across the infrared spectrum. This work introduces an attractive alternative to the use of hollow-core fibers or multimode solid-core fibers for diffraction-limited infrared beam delivery.

Nanosecond laser coupling for increased filament ablation.

Laser filaments can project intensities sufficient to ablate materials at long ranges, but the clamping of a filament's intensity to ∼1014 W/cm2 limits the effective ablation of targets with which the laser pulses interact. We seek to identify regimes in which auxiliary radiation can be used to augment the ablation created by single filaments. In this work, the combination of an 800 nm, 50 fs beam at single filament intensity and a 1064 nm, 8 ns laser pulse is studied. The ablation of GaAs is quantitatively evaluated for varying interpulse delays. Under optimum conditions, an ∼threefold increase in the ablation is observed. The metrology and surface features of the resultant ablation craters are examined to gain insight on the mechanisms of ablation in the dual-pulse cases.

Broadband space-time wave packets propagating 70 m.

The propagation distance of a pulsed beam in free space is ultimately limited by diffraction and space-time coupling. "Space-time" (ST) wave packets are pulsed beams endowed with tight spatio-temporal spectral correlations that render them propagation-invariant. Here we explore the limits of the propagation distance for ST wave packets. Making use of a specially designed phase plate inscribed by gray-scale lithography and having a laser-damage threshold of ∼0.5 J/cm2, we synthesize a ST light sheet of width ≈700 µm and bandwidth ∼20 nm, and confirm a propagation distance of ≈70 m.

A decade of Australian and New Zealand orthopaedic publications: a bibliometric trend analysis from 2008 to 2018.

PURPOSE: We aimed to apply bibliometric tools to Australian and New Zealand orthopaedic publications produced between 2008 and 2018 to identify the most highly cited publications, author and institution collaboration networks and topic trends. Analysis of the literature can highlight areas of emerging interest and knowledge gaps, and direct future research. METHODS: A systematic search was conducted using Clarivate Analytics Web of Science. Citation analysis was carried out using Web of Science. Collaboration networks were constructed using chord diagrams. Trends in publication topics were analysed using simple linear regression to find the rate of change of publication volume on each topic. RESULTS: A total of 3097 publications contributed to by 8855 individual authors met inclusion criteria. Across the study period, there was a large increase in the annual volume of publications on the topic of ACL (Anterior Cruciate Ligament) surgery. We also found that collaboration between Australian and New Zealand authors was very low with only 1% (n = 31) of publications including authors from both countries and 0.4% (n = 12) including orthopaedic surgeons or trainees from both. CONCLUSIONS: Publications on ACL surgery have increased over the past decade, likely due to the presence of competing surgical approaches and the recently recognized risk of osteoarthritis following ACL reconstruction. The overall collaboration between Australian and New Zealand authors was very low which lends itself to opportunities for future research.

Synthesizing broadband propagation-invariant space-time wave packets using transmissive phase plates.

Space-time wave packets are a class of pulsed optical beams that are diffraction-free and dispersion-free in free space by virtue of introducing a tight correlation between the spatial and temporal degrees of freedom of the field. Such wave packets have been recently synthesized in a novel configuration that makes use of a spatial light modulator to realize the required spatio-temporal correlations. This arrangement combines pulse-modulation and beam-shaping to assign one spatial frequency to each wavelength according to a prescribed correlation function. Relying on a spatial light modulator results in several limitations by virtue of their pixelation, small area, and low energy-handling capability. Here we demonstrate the synthesis of space-time wave packets with one spatial dimension kept uniform - that is, light sheets - using transparent transmissive phase plates produced by a gray-scale lithography process. We confirm the diffraction-free behavior of wave packets having a bandwidth of 0.25 nm (filtered from a typical femtosecond Ti:sapphire laser) and 30 nm (a multi-terawatt femtosecond laser). This work paves the way for developing versatile high-energy light bullets for applications in nonlinear optics and laser machining.

Rotator cuff contact pressures at the tendon-implant interface after anatomic total shoulder arthroplasty using a metal-backed glenoid component.

BACKGROUND: Rotator cuff tears following anatomic total shoulder arthroplasty increase with duration of follow-up. This study aimed to evaluate contact pressure between the rotator cuff tendons and prosthesis after anatomic total shoulder arthroplasty and compare these with the tendon-contact pressures in the native shoulder. METHODS: Eight entire upper extremities were mounted onto a testing apparatus, and simulated muscle loading was applied to each rotator cuff tendon with the shoulder positioned in abduction, internal rotation, and external rotation. Pressure-sensitive film placed between each tendon and bone was used to measure the resultant tendon contact pressures. Experiments were repeated after anatomic total shoulder arthroplasty using standardized implant sizes, and pressure-sensitive film was used to evaluate tendon-prosthesis contact pressure. RESULTS: Both joint angle and shoulder joint replacement surgery had significant effects on the maximum contact pressure measured between the humeral head and all rotator cuff tendons (P < .05) except the teres minor. The supraspinatus demonstrated a significantly larger peak tendon contact pressure after surgery at 45° of abduction relative to that in the native shoulder (mean difference, 0.2 MPa; P = .031), while the subscapularis had a significantly larger maximum contact pressure at 10° of abduction (mean difference, 0.45 MPa; P = .032) and 90° of abduction (mean difference, 0.80 MPa; P = .008) postoperatively. CONCLUSION: Anatomic total shoulder arthroplasty results in significantly larger tendon contact pressures relative to those in the native shoulder. High tendon contact pressures may ultimately predispose rotator cuff tendons to postoperative wear-induced damage and tearing.

Fabrication of computer-generated holograms using femtosecond laser direct writing.

We demonstrate a single-step fabrication method for computer-generated holograms based on femtosecond laser direct writing. Therefore, a tightly arranged longitudinal waveguide array is directly inscribed into a transparent material. By tailoring the individual waveguide length, the phase profile of an incident laser beam can be arbitrarily adapted. The approach is verified in common borosilicate glass by inscribing a designed phase hologram, which forms the desired intensity pattern in its far field. The resulting performance is analyzed, and the potential as well as limitations of the method are discussed.

Divided-pulse amplification to the joule level.

Divided-pulse amplification (DPA) has proven to be a valuable tool in scaling the peak power of diode-pumped ytterbium-doped amplifiers to beyond the single-pulse threshold for parasitic nonlinear effects. DPA enables the amplification of picosecond pulses in solid-state amplifiers with limited bandwidth beyond the single-pulse damage threshold. In this Letter, we demonstrate DPA of picosecond pulses in a flashlamp-pumped Nd:YAG amplifier for the first time, to the best of our knowledge, yielding a combined pulse energy of 167 mJ.