Neodymium laser-pumped ultra-low noise tunable Brillouin fiber laser around 920†nm.

We have developed an ultra-low noise tunable Brillouin fiber laser exhibiting three orders of magnitude better frequency noise performance than the Neodymium-doped fiber laser pump and remarkable optical signal-to-noise ratio exceeding 80 dB suitable for immediate applications in coherent nonlinear conversion, quantum computing and underwater communications. In addition, we have implemented a custom optical phase-locked loop to ensure long-term stable operation and have investigated its impact on frequency noise. We demonstrate the power scalability of the single frequency (Hz-class) Brillouin laser, delivering over 500 mW with tunability across the 900 nm to 930 nm range in an all-fiber fully polarization-maintaining architecture.

Watt-level deep-UV subnanosecond laser system based on Nd-doped fiber at 229†nm.

We report an efficient deep-UV master-oscillator power amplifier (MOPA) laser system at 229 nm that generates 350 ps pulses at 2 MHz repetition rate with an average power of 1.2 W. The use of a polarization-maintaining large mode area neodymium-doped fiber operating on the 4F3/2→4I9/2 transition allows high-power laser emission of up to 28 W near 915 nm in the sub-nanosecond regime with low spectral broadening. Two nonlinear frequency conversion stages (LBO + BBO crystals) in a single-pass configuration directly convert the IR laser emission to deep UV. This laser demonstrates the great potential of Nd3+-doped fiber lasers to produce high-power deep-UV emission.

In-band pumped Tm,Ho:LiYF4 waveguide laser.

A 4.5 at.% Tm, 0.5 at.% Ho:LiYF4 planar waveguide (thickness: 25 µm) grown by Liquid Phase Epitaxy is in-band pumped by a Raman fiber laser at 1679 nm (the 3H6 → 3F4 Tm3+ transition). A continuous-wave waveguide laser generates a maximum output power of 540 mW at 2051nm with a slope efficiency of 32.6%, a laser threshold of 337 mW and a linear laser polarization (π). This represents the highest output power extracted from any Tm,Ho waveguide laser. No parasitic Tm3+ colasing is observed. The waveguide propagation losses are determined to be as low as 0.19 dB/cm.

Mode-locked all-PM Nd-doped fiber laser near 910 nm.

We present a compact passively mode-locked fiber laser emitting near 910 nm with an all-polarization-maintaining fiber laser architecture. The ring-cavity laser configuration includes a core-pumped neodymium-doped fiber as a gain medium and a semiconductor saturable absorber mirror as a passive mode-locking element. A bandpass filter is used to suppress parasitic emission near 1.06 µm and allows wavelength tuning between 903 and 912 nm. The laser operates in a highly stable and self-starting all-normal-dispersion regime with a minimum pulse duration of 8 ps at 28.2 MHz pulse repetition rate and 0.2 nJ maximum pulse energy. A single-pass amplifier stage increases the pulse energy up to 1.5 nJ, and pulse compression with a pair of gratings is demonstrated with nearly Fourier transform limited pulses.

Linearly-polarized pulsed Nd-doped fiber MOPA at 905†nm and frequency conversion to deep-UV at 226†nm.

We present the first frequency-quadrupled linearly-polarized Q-switched neodymium-doped fiber laser generating > 500 mW average power at 226 nm. For this purpose, an amplified Q-switched oscillator using novel large-mode-area (LMA) fibers and generating up to 24 W average power (15 kW peak power) at 905 nm was developed. Two nonlinear frequency conversion stages using a LBO crystal for SHG and a BBO crystal for FHG generate respectively up to 4.9 W average power in the deep blue at 452 nm and a maximum of 510 mW average power in the deep ultra-violet (DUV) at 226 nm. Performance limitations and further improvements are discussed.

Tm3+ and Ho3+ colasing in in-band pumped waveguides fabricated by femtosecond laser writing.

We report on the first, to the best of our knowledge, in-band pumped Tm3+,Ho3+ codoped waveguide (WG) laser. A depressed-index surface channel WG (type III) with a 50 µm half-ring cladding is fabricated in a 5 at. % Tm3+, 0.5 at. % Ho3+:KLu(WO4)2 crystal by femtosecond pulse direct laser writing. Under in-band pumping by a 1679 nm Er Raman fiber laser, Tm3+ and Ho3+ colasing is observed in the WG and explained by bidirectional energy transfer. The maximum total output power at ∼1942nm(Tm3+) and 2059 nm (Ho3+) is 448 mW with a slope efficiencyM of 40.6%, which is a record high for this type of WG lasers. The maximum output power of the Ho laser reaches 144 mW.

Incidence and characteristics of cerebral hypoxia after craniectomy in brain-injured patients: a cohort study.

OBJECTIVE: After craniectomy, although intracranial pressure (ICP) is controlled, episodes of brain hypoxia might still occur. Cerebral hypoxia is an indicator of poor outcome independently of ICP and cerebral perfusion pressure. No study has systematically evaluated the incidence and characteristics of brain hypoxia after craniectomy. The authors' objective was to describe the incidence and characteristics of brain hypoxia after craniectomy. METHODS: The authors included 25 consecutive patients who underwent a craniectomy after traumatic brain injury or intracerebral hemorrhage and who were monitored afterward with a brain tissue oxygen pressure monitor. RESULTS: The frequency of hypoxic values after surgery was 14.6% despite ICP being controlled. Patients had a mean of 18 ± 23 hypoxic episodes. Endotracheal (ET) secretions (17.4%), low cerebral perfusion pressure (10.3%), and mobilizing the patient (8.6%) were the most common causes identified. Elevated ICP was rarely identified as the cause of hypoxia (4%). No cause of cerebral hypoxia could be determined 31.2% of the time. Effective treatments that were mainly used included sedation/analgesia (20.8%), ET secretion suctioning (15.4%), and increase in fraction of inspired oxygen or positive end-expiratory pressure (14.1%). CONCLUSIONS: Cerebral hypoxia is common after craniectomy, despite ICP being controlled. ET secretion and patient mobilization are common causes that are easily treatable and often not identified by standard monitoring. These results suggest that monitoring should be pursued even if ICP is controlled. The authors' findings might provide a hypothesis to explain the poor functional outcome in the recent randomized controlled trials on craniectomy after traumatic brain injury where in which brain tissue oxygen pressure was not measured.

Widely tunable in-band-pumped Tm:CaF2 laser.

This Letter presents the efficient laser operation of a Tm:CaF2 crystal in-band pumped at 1610 nm by an Er-Yb-codoped fiber laser system. A laser slope efficiency of 55% (versus incident pump power) was achieved in a continuous-wave regime, with a maximum output power of 1.25 W at ∼1.88µm in a nearly diffraction-limited beam (M2=1.14). We also demonstrated a continuous tuning range of 180 nm, which extends to short wavelengths down to 1773 nm.

Ultrafast laser inscribed waveguide lasers in Tm:CALGO with depressed-index cladding.

Depressed-index buried and surface channel waveguides (type III) are produced in a bulk 3.5 at.% Tm3+:CALGO crystal by femtosecond direct-laser-writing at kHz repetition rate. The waveguides are characterized by confocal microscopy and µ-Raman spectroscopy. Under in-band-pumping at 1679 nm (3H6 → 3F4 transition) by a Raman fiber laser, the buried channel waveguide laser with a circular cladding (diameter: 60 µm) generated a continuous-wave output power of 0.81 W at 1866-1947 nm with a slope efficiency of 71.2% (versus the absorbed pump power) and showed a laser threshold of 200 mW. The waveguide propagation losses were as low as 0.3 ± 0.2 dB/cm. The laser performance under in-band pumping was superior compared pumping at ∼800 nm (3H6 → 3H4 transition), i.e., the convetional pump wavelength. Vibronic laser emission from the WG laser above 2 µm is also achieved. The low-loss behavior, the broadband emission properties and good power scaling capabilities indicate the suitability of Tm3+:CALGO waveguides for mode-locked laser operation at ∼2 µm.

Dissipative soliton resonance in a mode-locked Nd-fiber laser operating at 927 nm.

We demonstrate for the first time, to our knowledge, an all-polarization-maintaining double-clad neodymium fiber laser operating in the dissipative soliton resonance (DSR) regime where stable mode-locking is achieved using a nonlinear amplifying loop mirror (NALM) with large normal dispersion in a figure-8 cavity design. The laser thereby generates square-shaped nanosecond pulses whose duration linearly scales with pump power from 0.5 up to 6 ns, with a maximum energy of 20 nJ. In addition, output pulses feature a remarkably narrow bandwidth of 60 pm along with a signal-to-noise ratio higher than 80 dB. This study then paves the way toward using such DSR-based sources for efficient frequency doubling in the blue spectral range.

In-band pumping of Tm:LiYF4 channel waveguide: a power scaling strategy for ∼2 µm waveguide lasers.

We report on a novel power scaling strategy for thulium waveguide (WG) lasers relying on in-band pumping by high-brightness Raman fiber lasers (RFLs) and the use of liquid-phase-epitaxy-grown fluoride crystalline thin films for better thermal management. Thulium channel WGs are produced by microstructuring the Tm3+:LiYF4/LiYF4 epitaxies via diamond-saw dicing. They are pumped by a RFL based on an erbium master oscillator power amplifier and a GeO2-doped silica fiber and emit polarized output at 1679 nm. A CW in-band-pumped (H63→F43) Tm3+:LiYF4 WG laser generates up to 2.05 W of a linearly polarized single-transverse-mode output at 1881 nm with a slope efficiency of 78.3% and a laser threshold of only 12 mW (versus the absorbed pump power).

Minimal PaO2 threshold after traumatic brain injury and clinical utility of a novel brain oxygenation ratio.

OBJECTIVE: Avoiding decreases in brain tissue oxygenation (PbtO2) after traumatic brain injury (TBI) is important. How best to adjust PbtO2 remains unclear. The authors investigated the association between partial pressure of oxygen (PaO2) and PbtO2 to determine the minimal PaO2 required to maintain PbtO2 above the hypoxic threshold (> 20 mm Hg), accounting for other determinants of PbtO2 and repeated measurements in the same patient. They also explored the clinical utility of a novel concept, the brain oxygenation ratio (BOx ratio = PbtO2/PaO2) to detect overtreatment with the fraction of inspired oxygen (FiO2). METHODS: A retrospective cohort study at an academic level 1 trauma center included 38 TBI patients who required the insertion of a monitor to measure PbtO2. Various determinants of PbtO2 were collected simultaneously whenever a routine arterial blood gas was drawn. A PbtO2/PaO2 ratio was calculated for each blood gas and plotted over time for each patient. All patients were managed according to a standardized clinical protocol. A mixed effects model was used to account for repeated measurements in the same patient. RESULTS: A total of 1006 data points were collected. The lowest mean PaO2 observed to maintain PbtO2 above the ischemic threshold was 94 mm Hg. Only PaO2 and cerebral perfusion pressure were predictive of PbtO2 in multivariate analysis. The PbtO2/PaO2 ratio was below 0.15 in 41.7% of all measures and normal PbtO2 values present despite an abnormal ratio in 27.1% of measurements. CONCLUSIONS: The authors' results suggest that the minimal PaO2 target to ensure adequate cerebral oxygenation during the first few days after TBI should be higher than that suggested in the Brain Trauma Foundation guidelines. The use of a PbtO2/PaO2 ratio (BOx ratio) may be clinically useful and identifies abnormal O2 delivery mechanisms (cerebral blood flow, diffusion, and cerebral metabolic rate of oxygen) despite normal PbtO2.

7.5 W blue light generation at 452 nm by internal frequency doubling of a continuous-wave Nd-doped fiber laser.

We present the first frequency-doubled neodymium-doped fiber laser generating multi-watt CW power near 450 nm. A bow-tie resonator incorporating a LBO nonlinear crystal is integrated within a Nd-doped fiber laser emitting near 900 nm. This scheme achieves an IR to blue conversion efficiency close to 55% without any active control of the internal resonant cavity. As a result, up to 7.5 W of linearly-polarized blue power is generated, with beam quality factors Mx2 ~1.0 and My2 ~1.5. A simple numerical model has been developed to optimize and analyse the IR to blue conversion efficiency in the resonant cavity. Performance limitations and prospects for further improvements are discussed.

2.3 µm Tm3+:YLF mode-locked laser.

A passively mode-locked Tm:YLF laser emitting at 2.3 µm is reported for the first time, to the best of our knowledge. The continuous-wave stable mode-locking operation is obtained with a semiconductor saturable absorber mirror at a repetition rate of 100 MHz. The average output power is 165 mW for a pulse duration of 94 ps.

Transverse mode selection in a Nd-doped fiber amplifier at 910 nm.

Selective amplifications of LP01 fundamental mode and higher order modes LP11 and LP01 are demonstrated in a double-pass Nd-doped LMA fiber amplifier operating at 910 nm. A multimode core fiber Bragg grating is employed to select a single guided mode by simply adjusting the wavelength of the seed signal. Although the M2 parameter of the output beam from the amplifier was ~2.5 in a single-pass configuration, a double-pass configuration with LP01 mode selection reduces the value of the M2 parameter to 1.06 in spite of the multimode nature of the core (V~5). In addition, it is shown that this amplifier configuration permits to lower both the power saturation and the parasitic emission at 1060 nm, which consequently increase the pump-to-signal conversion efficiency at 910 nm.

Risk of Delayed Intracranial Hemorrhage in Anticoagulated Patients with Mild Traumatic Brain Injury: Systematic Review and Meta-Analysis.

BACKGROUND: Delayed intracranial hemorrhage is a potential complication of head trauma in anticoagulated patients. OBJECTIVE: Our aim was to use a systematic review and meta-analysis to determine the risk of delayed intracranial hemorrhage 24 h after head trauma in patients who have a normal initial brain computed tomography (CT) scan but took vitamin K antagonist before injury. METHODS: EMBASE, Medline, and Cochrane Library were searched using controlled vocabulary and keywords. Retrospective and prospective observational studies were included. Outcomes included positive CT scan 24 h post-trauma, need for surgical intervention, or death. Pooled risk was estimated with logit proportion in a random effect model with 95% confidence intervals (CIs). RESULTS: Seven publications were identified encompassing 1,594 patients that were rescanned after a normal first head scan. For these patients, the pooled estimate of the incidence of intracranial hemorrhage on the second CT scan 24 h later was 0.60% (95% CI 0-1.2%) and the resulting risk of neurosurgical intervention or death was 0.13% (95% CI 0.02-0.45%). CONCLUSIONS: The present study is the first published meta-analysis estimating the risk of delayed intracranial hemorrhage 24 h after head trauma in patients anticoagulated with vitamin K antagonist and normal initial CT scan. In most situations, a repeat CT scan in the emergency department 24 h later is not necessary if the first CT scan is normal. Special care may be required for patients with serious mechanism of injury, patients showing signs of neurologic deterioration, and patients presenting with excessive anticoagulation or receiving antiplatelet co-medication.

Mode-locked Nd-doped fiber laser at 930 nm.

We report on a passively mode-locked neodymium-doped oscillator featuring a W-type fiber operating at 930 nm. Two different laser configurations with and without dispersion management are investigated to generate high-energy similaritons. Chirped pulses with 2.2 nJ energy that can be compressed to 126 fs are generated in the dispersion-managed cavity. The ANDI-fiber laser delivers parabolic pulses with 5.2 ps duration that can be compressed to 146 fs.

Safety and efficacy of CHOP for treatment of diffuse large B-cell lymphoma with different combination antiretroviral therapy regimens: SCULPT study.

BACKGROUND: Use of combination antiretroviral therapy (cART) and cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) with or without rituximab for treatment of diffuse large B-cell lymphoma (DLBCL) in HIV substantially increases response rates but may also increase toxicity, possibly due to antiretroviral-antineoplastic drug interactions. The objective of this study was to evaluate the frequency of complete remission (CR) of DLBCL in patients treated with CHOP while receiving a protease inhibitor (PI) versus a non-PI-based cART. METHODS: A retrospective multicentre pilot study was conducted in HIV-infected patients on cART treated for DLBCL with CHOP between 2002-2010 in three academic hospitals. RESULTS: A total of 34 patients were included with 65% and 35% of patients receiving a PI and non-PI-based cART, respectively. Baseline characteristics between groups were similar; overall 85% were male, median age was 43 years, 50% had an International Prognostic Index (IPI) of 2-3 and median CD4(+) T-cell count was 225 cells/mm(3). CR was achieved in 77% and 58% of patients in the PI and non-PI groups, respectively (P=0.21), with 65% and 63% of patients achieving 2-year overall survival (P=1.00). A multivariate analysis showed that lower IPI score alone was significantly associated with higher CR rates (P=0.05). Toxicity was similar between both groups. CONCLUSIONS: Similar efficacy and toxicity of CHOP was observed in patients receiving a PI and non-PI-based cART.

Coagulopathy after traumatic brain injury.

Traumatic brain injury has long been associated with abnormal coagulation parameters, but the exact mechanisms underlying this phenomenon are poorly understood. Coagulopathy after traumatic brain injury includes hypercoagulable and hypocoagulable states that can lead to secondary injury by either the induction of microthrombosis or the progression of hemorrhagic brain lesions. Multiple hypotheses have been proposed to explain this phenomenon, including the release of tissue factor, disseminated intravascular coagulation, hyperfibrinolysis, hypoperfusion with protein C activation, and platelet dysfunction. The diagnosis and management of these complex patients are difficult given the lack of understanding of the underlying mechanisms. The goal of this review is to summarize the current knowledge regarding the mechanisms of coagulopathy after blunt traumatic brain injury. The current and emerging diagnostic tools, radiological findings, treatment options, and prognosis are discussed.

Dynamical amplification of phase conjugation using a modulated optical feedback in a Nd:YVO4 laser.

We demonstrate an efficient dynamical amplification of phase conjugation in the gain medium of a diode-pumped Nd(3+)YVO4 solid-state laser via excitation of its relaxation oscillations. Consequently, enhancement in the modulated amplitude of the phase conjugate wave is observed with up to +30 dB compared to the classical homodyne approach.