Laser-guided real-time automatic target identification for endoscopic stone lithotripsy: a two-arm in vivo porcine comparison study.

INTRODUCTION AND OBJECTIVE: Thermal injuries associated with Holmium laser lithotripsy of the urinary tract are an underestimated problem in stone therapy. Surgical precision relies exclusively on visual target identification when applying laser energy for stone disintegration. This study evaluates a laser system that enables target identification automatically during bladder stone lithotripsy, URS, and PCNL in a porcine animal model. METHODS: Holmium laser lithotripsy was performed on two domestic pigs by an experienced endourology surgeon in vivo. Human stone fragments (4-6 mm) were inserted in both ureters, renal pelvises, and bladders. Ho:YAG laser lithotripsy was conducted as a two-arm comparison study, evaluating the target identification system against common lithotripsy. We assessed the ureters' lesions according to PULS and the other locations descriptively. Post-mortem nephroureterectomy and cystectomy specimens were examined by a pathologist. RESULTS: The sufficient disintegration of stone samples was achieved in both setups. Endoscopic examination revealed numerous lesions in the urinary tract after the commercial Holmium laser system. The extent of lesions with the feedback system was semi-quantitatively and qualitatively lower. The energy applied was significantly less, with a mean reduction of more than 30% (URS 27.1%, PCNL 52.2%, bladder stone lithotripsy 17.1%). Pathology examination revealed only superficial lesions in both animals. There was no evidence of organ perforation in either study arm. CONCLUSIONS: Our study provides proof-of-concept for a laser system enabling automatic real-time target identification during lithotripsy on human urinary stones. Further studies in humans are necessary, and to objectively quantify this new system's advantages, investigations involving a large number of cases are mandatory.

Infrared Laser Application to Wood Cutting.

While lasers are widely used across various industries, including woodworking, few studies to date have addressed the issue of cutting fresh wood. In the present investigation, wood stemming from fresh tree branches was cut at different laser powers and beam travel speeds. A fiber laser and a CO2 laser were used for the research. The cellular structures of the cut surfaces were examined, with some of them found to be covered with a layer of compacted, charred cells. This may be a favorable phenomenon, preventing the invasion of pathogens via the wounds caused by laser beam branch cutting in nurseries, plantations, and orchards.

Experimental Investigation of Actively Q-Switched Er3+:ZBLAN Fiber Laser Operating at around 2.8 µm.

A diode-pumped Q-switched Er3+:ZBLAN double-clad, single-transverse mode fiber laser is practically realized. The Q-switched laser characteristics as a function of pump power, repetition rate, and fiber length are experimentally investigated. The results obtained show that the Q-switched operation with 46 µJ pulse energy, 56 ns long pulses, and 0.821 kW peak power is achieved at a pulse repetition rate of 10 kHz. To the best of our knowledge, this is the highest-ever demonstrated peak power emitted from an actively Q-switched, single-transverse mode Er3+:ZBLAN fiber laser operating near 2.8 µm.

Correction: Prospective on using fibre mid-infrared supercontinuum laser sources for in vivo spectral discrimination of disease.

Correction for 'Prospective on using fibre mid-infrared supercontinuum laser sources for in vivo spectral discrimination of disease' by Angela B. Seddon et al., Analyst, 2018, 143, 5874-5887.

A Novel Laser Lithotripsy System with Automatic Real-Time Urinary Stone Recognition: Computer Controlled Ex Vivo Lithotripsy is Feasible and Reproducible in Endoscopic Stone Fragmentation.

PURPOSE: Urinary stone treatment has been strongly influenced by advances in technology. Nevertheless, the photonic characteristics of stones as the treatment target have been neglected. Monitoring fluorescence spectra is sufficient for automatic target differentiation and laser feedback control as previously described. We investigated the characteristics of fluorescence signals and the clinical practicability of real-time laser feedback control during lithotripsy. MATERIALS AND METHODS: Fluorescence excitation light was superimposed on a holmium laser beam into the treatment fiber. Spectra were recorded and signal amplitude changes were analyzed during increases in distance between the fiber tip and the stone to identify the optimal threshold level for stone recognition. Ho:YAG lithotripsy was performed under in vitro surgical conditions in porcine tissue while our feedback system autonomously controlled the laser impulse release during lithotripsy. The tissue was then endoscopically and macroscopically examined for laser induced lesions. RESULTS: Mean ± SD autofluorescence signal amplitudes from urinary stone samples varied between 142 ± 29 and 1,521 ± 152 ADU while tissue and endoscope coating emission was negligible. Signal amplitude decreased rapidly at distances larger than 1 to 2 mm. Clinically reliable threshold values for target recognition could be set to prevent laser pulse emission if the stone was out of range or urothelial tissue might be harmed by laser irradiation. We observed no incorrectly released laser pulse or injury to tissue during autonomously controlled holmium laser lithotripsy. CONCLUSIONS: Our laboratory study strengthens the evidence that tracking real-time autofluorescence spectra during endoscopic stone surgery via automatic feedback control of the laser impulse release may become a potentially useful clinical tool for surgeons who navigate in the upper urinary tract.

Prospective on using fibre mid-infrared supercontinuum laser sources for in vivo spectral discrimination of disease.

Mid-infrared (MIR) fibre-optics may play a future role in in vivo diagnosis of disease, including cancer. Recently, we reported for the first time an optical fibre based broadband supercontinuum (SC) laser source spanning 1.3 to 13.4 µm wavelength to cover the spectral 'fingerprint region' of biological tissue. This work has catalysed the new field of fibre MIR-SC and now very bright sources equivalent to a 'few synchrotrons' have been demonstrated in fibre. In addition, we have made record transparency MIR fibre for routeing the MIR light and reported first-time MIR photoluminescence (with long lifetime) in small-core, rare earth ion doped, MIR fibre - an important step towards MIR fibre lasing at >4 µm wavelength for pumping fibre MIR-SC. First time fibre MIR-SC spectroscopic imaging of colon tissue is described at wavelengths in the 'fingerprint region'.

Ho:KY(WO4)2 thin-disk laser passively Q-switched by a GaSb-based SESAM.

A Holmium thin-disk laser based on a 3 at.% Ho:KY(WO4)2 / KY(WO4)2 epitaxy and single-bounce pumping by a 1960 nm Tm-fiber laser is passively Q-switched with a GaSb-based quantum-well semiconductor saturable absorber mirror. It generates an average output power of 551 mW at 2056 nm with a slope efficiency of 44% (with respect to the absorbed pump power). The best pulse characteristics (energy and duration) are 4.1 µJ / 201 ns at a repetition rate of 135 kHz and the conversion efficiency with respect to the continuous-wave regime is as high as 93%.

Holmium thin-disk laser based on Ho:KY(WO4)2/KY(WO4)2 epitaxy with 60% slope efficiency and simplified pump geometry.

We report on the first holmium (Ho3+) monoclinic double tungstate thin-disk laser. It is based on a 250 µm thick 3 at. % Ho:KY(WO4)2 active layer grown on a (010)-oriented KY(WO4)2 substrate. When pumped by a Tm-fiber laser at 1960 nm with a single-bounce (single double-pass) pump geometry, the CW Ho:KY(WO4)2 thin-disk laser generated 1.01 W at 2057 nm, corresponding to a slope efficiency η of 60% and a laser threshold of only 0.15 W. Implementing a double-bounce (second double-pass) for the pump, the output of this laser was scaled to 1.57 W with η=55%. The maximum stimulated emission cross section σSE of the Ho3+ ions in the epitaxial layer reaches 2.5×10-20 cm2 at 2056.5 nm for E‖Nm. The Ho:KY(WO4)2 epitaxial structures are promising for multi-watt mode-locked thin-disk lasers at ∼2.06 µm.

Mid-infrared supercontinuum generation to 12.5µm in large NA chalcogenide step-index fibres pumped at 4.5µm.

We present numerical modeling of mid-infrared (MIR) supercontinuum generation (SCG) in dispersion-optimized chalcogenide (CHALC) step-index fibres (SIFs) with exceptionally high numerical aperture (NA) around one, pumped with mode-locked praseodymium-doped (Pr(3+)) chalcogenide fibre lasers. The 4.5um laser is assumed to have a repetition rate of 4MHz with 50ps long pulses having a peak power of 4.7kW. A thorough fibre design optimisation was conducted using measured material dispersion (As-Se/Ge-As-Se) and measured fibre loss obtained in fabricated fibre of the same materials. The loss was below 2.5dB/m in the 3.3-9.4µm region. Fibres with 8 and 10µm core diameters generated an SC out to 12.5 and 10.7µm in less than 2m of fibre when pumped with 0.75 and 1kW, respectively. Larger core fibres with 20µm core diameters for potential higher power handling generated an SC out to 10.6µm for the highest NA considered but required pumping at 4.7kW as well as up to 3m of fibre to compensate for the lower nonlinearities. The amount of power converted into the 8-10µm band was 7.5 and 8.8mW for the 8 and 10µm fibres, respectively. For the 20µm core fibres up to 46mW was converted.

Q-switched Ho:Lu2O3 laser at 2.12 µm.

We report on a Q-switched Ho:Lu2O3 laser resonantly pumped by a GaSb-based laser diode stack at 1.9 µm. The maximum output energy extracted from the compact plano-plano acousto-optically Q-switched resonator was 8 mJ at a 100 Hz pulse repetition rate, while the peak power was 40 kW. The laser wavelength was 2.124 µm.

Holmium-doped Lu2O3, Y2O3, and Sc2O3 for lasers above 2.1 µm.

Efficient room-temperature laser operation was obtained in the wavelength range from 2117 nm to 2134 nm with Ho:Lu(2)O(3) and Ho:Y(2)O(3) as the active materials. With an FBG-stabilized Tm-doped fiber laser as the pump source, the maximum slope efficiency and output power of the Ho:Y(2)O(3) laser were 63% and 18.8 W, respectively. With Ho:Lu(2)O(3) the respective values were 76% and 25.2 W. With Ho:Sc(2)O(3) as the active material the accessible wavelength range could be expanded to 2158 nm in a diode-pumped setup.

Directly diode-pumped high-energy Ho:YAG oscillator.

We report on the high-energy laser operation of an Ho:YAG oscillator resonantly pumped by a GaSb-based laser diode stack at 1.9 µm. The output energy was extracted from a compact plano-concave acousto-optically Q-switched resonator optimized for low repetition rates. Operating at 100 Hz, pulse energies exceeding 30 mJ at a wavelength of 2.09 µm were obtained. The corresponding pulse duration at the highest pump power was 100 ns, leading to a maximum peak power above 300 kW. Different pulse repetition rates and output coupling transmissions of the Ho:YAG resonator were studied. In addition, intracavity laser-induced damage threshold measurements are discussed.

Efficient diode-pumped laser operation of Tm:Lu2O3 around 2 µm.

We report on the first diode-pumped laser operation of thulium-doped Lu2O3. With a very compact setup an output power of 75 W and slope efficiencies of around 40% with respect to the incident pump power were achieved at room temperature. Free running laser operation was observed at wavelengths of 2065 nm and 1965 nm. With a birefringent filter the wavelength could continuously be tuned from 1922 nm to 2134 nm. The thermal conductivity of Tm:Lu2O3 was measured for different dopant concentrations and is compared to the one of thulium-doped YAG.