A versatile high-average-power ultrafast infrared driver tailored for high-harmonic generation and vibrational spectroscopy.

We report on an ultrafast infrared optical parametric chirped-pulse amplifier (OPCPA), pumped by a 200-W thin-disk Yb-based regenerative amplifier at a repetition rate of 100 kHz. The OPCPA is tunable in the spectral range 1.4-3.9 [Formula: see text]m, generating up to 23 W of < 100-fs signal and 13 W of < 200-fs idler pulses for infrared spectroscopy, with additional spectral filtering capabilities for Raman spectroscopy. The OPCPA can also yield 19 W of 49-fs 1.75-[Formula: see text]m signal or 5 W of 62-fs 2.8-[Formula: see text]m idler pulses with active carrier-to-envelope-phase (CEP) stabilisation for high-harmonic generation (HHG). We illustrate the versatility of the laser design, catering to various experimental requirements for probing ultrafast science.

Measurement of nonlinear refractive indices of bulk and liquid crystals by nonlinear chirped interferometry.

The nonlinear refractive indices (n2) of a selection of bulk (LiB3O5, KTiOAsO4, MgO:LiNbO3, LiGaS2, ZnSe) and liquid (E7, MLC2132) crystals are measured at 1030 nm in the sub-picosecond regime (200 fs) by nonlinear chirped interferometry. The reported values provide key parameters for the design of near- to mid-infrared parametric sources, as well as all-optical delay lines.

Spectral coherence properties of continuum generation in bulk crystals.

The stability of the phase difference between two white-light continua, generated from the same 180-fs pulses at ≃1035 nm, is assessed by a modified Bellini-Hänsch interferometer. Mutual spectral phase stability is studied and quantified as a function of several parameters: pulse energy, position of the nonlinear crystal with respect to the beam waist and interaction length. Our results show that intrapulse decoherence may significantly contribute to the measured CEP noise floor. In addition, spectrally-resolved intensity-to-phase coupling coefficients are measured and stability regions are identified.

High-speed chemical imaging of dynamic and histological samples with stimulated Raman micro-spectroscopy.

We report a shot noise limited high-speed stimulated Raman microscopy platform allowing to acquire molecular vibrational spectra over 200 cm-1 in 12 µs at a scan rate of 40kHz. Using spectral focusing together with optimized acousto-optics programmable dispersive filters, the designed low noise imaging platform performs chemical imaging of dynamical processes such as Mannitol crystal hydration and reaches a signal to noise ratio sufficient to perform label free histological imaging on frozen human colon tissue slides.

Sub-second hyper-spectral low-frequency vibrational imaging via impulsive Raman excitation.

Real-time vibrational microscopy has been recently demonstrated by various techniques, most of them utilizing the well-known schemes of coherent anti-stokes Raman scattering and stimulated Raman scattering. These techniques readily provide valuable chemical information mostly in the higher vibrational frequency regime (>400 cm-1). Addressing the low vibrational frequency regime (<200 cm-1) is challenging due to the usage of spectral filters that are required to isolate the signal from the Rayleigh scattered excitation field. In this Letter, we report on rapid, high-resolution, low-frequency (<130 cm-1) vibrational microscopy using impulsive coherent Raman excitation. By combining impulsive excitation with a fast acousto-optic delay line, we detect the Raman-induced optical Kerr lensing and spectral shift effects with a 25 µs pixel dwell time to produce shot-noise limited, low-frequency hyper-spectral images of various samples.

Dispersion control for temporal contrast optimization.

We investigate the temporal contrast of the Light Wave Synthesizer 20 (LWS-20): a powerful, few-cycle source based on the optical parametric synthesizer principle. Saturation effects in the RF amplifier driving the acousto-optic programmable dispersive filter (AOPDF) were found to degrade the coherent contrast for non-monotonic group delay corrections. We subsequently present a new dispersion scheme and design a novel transmission grism-based stretcher optimized for LWS-20. The resulting temporal contrast of the amplified, compressed output pulses is improved by 2-4 orders of magnitude compared to the former design.

Highly stable, 15 W, few-cycle, 65 mrad CEP-noise mid-IR OPCPA for statistical physics.

We demonstrate a 100 kHz optical parametric chirped-pulse amplifier delivering under 4-cycle (38 fs) pulses at ~3.2 µm with an average power of 15.2 W with a pulse-to-pulse energy stability <0.7% rms and a single-shot CEP noise of 65 mrad RMS over 8h. This source is continuously monitored, by using a fast 100 kHz data acquisition device, and presents an extreme stability, in the short and long terms.

Self-compression in a multipass cell.

We demonstrate self-compression of short-wavelength infrared pulses in a multipass cell (MPC) containing a plate of silica. Nonlinear propagation in the cell in the anomalous dispersion regime results in the generation of 14 µJ 22 fs pulses at 125 kHz repetition rate and 1550 nm wavelength. Periodic focusing inside the cell allows us to circumvent catastrophic self-focusing, despite an output peak power of 440 MW well beyond the critical power in silica of 10 MW. This technique allows straightforward energy scaling of self-compression setups and control over the spatial manifestation of Kerr nonlinearity. More generally, MPCs can be used to perform, at higher energy levels, temporal manipulations of pulses that have been previously demonstrated in waveguides.

Fascia Iliaca Compartment Block Efficacy in Resource-poor Emergency Departments.

INTRODUCTION: Although the fascia iliaca compartment block (FICB) seems to be an ideal technique for femoral neck and shaft fractures occurring in resource-poor settings, it has been unclear how effective it is when used by emergency physicians (EP) with little training in the technique, using equipment, medications and methods that differ from those commonly available in developed countries. This series was designed to demonstrate that EPs in a resource-poor setting can provide effective analgesia for femur fractures with anatomic landmark-guided FICBs, clinician-compounded lidocaine-epinephrine (1:100,000), and a standard injection needle. METHODS: Over a three-month period, patients ≥12 years old presenting to the emergency department with hip or femur fractures and a Likert visual analogue scale >4 had an EP-administered FICB. EPs used a standard intramuscular needle and a lidocaine-epinephrine solution they compounded at the bedside and located the injection site using only anatomic landmarks. EPs evaluated the patient's pain level at 30 minutes and at two hours post-FICB. We also reviewed articles since 2016 that describe the FICB. RESULTS: We enrolled a non-consecutive sample of 10 patients in the case series. Five had femoral neck (hip) fractures and five had femoral shaft fractures. All patients had a reduction in their pain levels after the FICB. On average, the block took effect about three minutes after injection. At 30 minutes all patients reported clinically meaningful pain reduction. The analgesic effect of the compounded agent lasted approximately 200 minutes. No adverse effects were reported. No published journal articles about FICB since 2016 were from resource-poor settings, and only one was from a developing country. CONCLUSION: This series suggests that the FICB is effective even when performed with the minimal materials that are usually available in resource-poor settings. Methods such as this, which use simplified clinical tests and techniques applicable in resource-poor settings, can assist global emergency medicine (EM). We can assist global EM by similarly finding methods to simplify useful clinical tests and techniques that can be used in resource-poor settings.

Dynamical optical response of nematic liquid crystal cells through electrically driven Fréedericksz transition: influence of the nematic layer thickness.

A dynamical optical characterization of planar nematic liquid-crystal cells electrically driven through the Fréedericksz transition is presented. Our method involves applying voltage steps with different starting voltage close to the Fréedericksz threshold. Measurements are performed on cells with various thickness, from a few microns up to 180µm, and highlight the transient molecular disorder occurring close to the Fréedericksz transition. We show that the transient disorder affects the molecular arrangement mainly in the reorientational plane of the splay motion induced by the planar cell geometry. Moreover, a disorder quantification in terms of optical transmission losses and temporal dynamics enables us to picture the Fréedericksz transition. This characterization provides the identification of the electrical driving conditions for which the effect of the reorientational disorder is minimized. When comparing cells with various thicknesses, it results that thick cells are characterized by a much smoother transition with respect to the conventional step-like Fréedericksz transition of the thin cells, hence, thick cells can be dynamically driven over a large range of voltages, even below the Fréedericksz threshold. The results are discussed in view of novel electro-optical applications of thick layers of nematics. As an example, the experimental conditions for realizing a rapid birefringence scan and the achievement of a large and tunable group delay for femtosecond pulses are presented.

Tunable angular shearing interferometer based on wedged liquid crystal cells.

The concept of a liquid crystal wedge as a tunable angular shearing interferometer is introduced and demonstrated to combine both high stability and high tunability. Different wedges are fabricated from planar aligned nematic liquid crystal cells with thickness gradients. These wedges are shown to produce stable interferograms from the polarization interference between the ordinary and extraordinary waves propagating in different directions at the output of the cell. The fringe periods, ranging from 70 µm to 1.25 mm, can be precisely controlled by a low voltage. Despite the wedge-shaped structure, no inhomogeneity has been detected when the wedge is driven adiabatically and the interferograms are uniform over regions as large as 5×5 mm. Moreover, dynamical measurements show that the wedges behave as a succession of multiple cells with different thickness, giving rise to a moving front of stabilizing fringes when driven dynamically. All the observations show that the device is suitable for large beam size and tunable shearing interferometry, with attractive features for applications such as phase sensing, photoalignment or photolithography.

Epidemiology and mapping of serious and fatal road traffic injuries in Guyana: results from a cross-sectional study.

OBJECTIVE: To describe the epidemiology of Guyana's road traffic injuries and perform the first geocoding of road traffic injuries in this setting. METHODS: This was a registry-based retrospective cross-sectional study investigating collisions resulting in serious and fatal injuries. Police reports from two police divisions were used to identify victim, second party (ie, non-victim) and collision characteristics of all serious and fatal collisions between January 2012 and June 2015. Collisions with available location data were geocoded using Geographic Information Systems. Distributions of characteristics were compared for urban and rural areas. Multivariable logistic regression was used to assess variables associated with fatal collisions. RESULTS: The study included 751 collisions, resulting in 1002 seriously or fatally injured victims. Fatally injured victims tended to be older, male and either pedestrians or cyclists. Fatal collisions tended to take place in rural areas, occur on weekends and involve speeding. Fifty-three per cent of fatalities occurred due to non-motorised road users being struck by motorised road users, and the most common fatal collision type was between pedestrians and motor vehicles (35%). The distribution of collisions was similar for urban (43.8%) and rural (56.2%) areas. Fatal collisions were more likely to occur in rural settings. CONCLUSIONS: Road traffic injuries pose a considerable public health burden in Guyana. These results suggest a pattern of high mortality in rural collisions and a disproportionate burden of injuries on vulnerable road users. The spatial distribution of collisions should be considered in order to target interventions and improve road traffic safety.

High-speed stimulated hyperspectral Raman imaging using rapid acousto-optic delay lines.

Stimulated Raman scattering (SRS) is a powerful, label-free imaging technique that holds significant potential for medical imaging. To allow chemical specificity and minimize spectral distortion in the imaging of live species, a high-speed multiplex SRS imaging platform is needed. By combining a spectral focusing excitation technique with a rapid acousto-optic delay line, we demonstrate a hyperspectral SRS imaging platform capable of measuring a 3-dB spectral window of ∼200 cm-1 within 12.8 µs with a scan rate of 30 KHz. We present hyperspectral images of a mixture of two different microsphere polymers as well as live fungal cells mixed with human blood.

4-W, 100-kHz, few-cycle mid-infrared source with sub-100-mrad carrier-envelope phase noise.

We demonstrate an optical parametric chirped-pulse amplifier delivering 4-cycles (38-fs) pulses centered around 3.1 µm at 100-kHz repetition rate with an average power of 4 W and an undersampled single-shot carrier-envelope phase noise of 81 mrad recorded over 25 min. The amplifier is pumped by a ~1.1 ps, Yb-YAG, thin-disk regenerative amplifier and seeded with a supercontinuum generated in bulk YAG from the same pump pulses. Carrier-envelope phase stability is passively achieved through difference-frequency generation between pump and seed pulses. An additional active stabilization at 10 kHz combining 2f-to-f interferometry and a LiNbO3 acousto-optic programmable dispersive filter achieves a record low phase noise.

Supercontinuum-seeded few-cycle mid-infrared OPCPA system.

We propose and demonstrate an OPCPA architecture emitting few-cycle pulses at 3070 nm and 1550 nm based on a high-energy femtosecond ytterbium-doped fiber amplifier pump. The short pump pulse duration allows direct seeding by a supercontinuum in the 1.4 - 1.7 µm signal range, generated in bulk YAG. It also allows a simplified dispersion management along the system and broad optical gain bandwidth. The dual output system delivers 20 µJ, 49 fs signal pulses at 1550 nm and 10 µJ, 72 fs idler pulses at 3070 nm. Power scaling limitations due to beam distortion in the last MgO:PPLN-based OPCPA stage are discussed and investigated.

Continuously tunable femtosecond delay-line based on liquid crystal cells.

We introduce a new device for group and phase delay steering of femtosecond pulse trains that makes use of cascaded, electrically driven, nematic liquid-crystal cells. Based on this approach we demonstrate a continuously tunable optical delay line. The simple collinear implementation with no moving parts enables to shape the achievable temporal range with sub-femtosecond accuracy. By appropriately choosing the bias voltages applied to the cascaded cells, the imparted group delay can be made either positive or negative and precisely adjusted. Moreover, independent control of the group delay and the phase of femtosecond pulses is demonstrated.

Spectral and spatial full-bandwidth correlation analysis of bulk-generated supercontinuum in the mid-infrared.

We report the measurement of spectral and spatial correlations in supercontinua generated by focusing microjoule pulses from a femtosecond ytterbium-doped fiber amplifier laser in bulk YAG. The measurement is full-bandwidth at a repetition rate of 1 MHz owing to the use of time-stretch dispersive Fourier transform technique. In contrast with fiber-based supercontinuum generation, our results show an excellent stability of the spectral and spatial properties of the output supercontinuum, with an essentially correlated behavior in the 1.4-1.7 µm wavelength range. These results provide strong ground for the development of supercontinuum-seeded ultrafast optical parametric amplifier systems in the mid-infrared using ytterbium lasers as pump sources.

Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system.

We present the first carrier-envelope-phase stable chirped-pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including cross-polarized wave (XPW) filtering technique and a high-energy grism-based compressor. The 8 mJ, 22 fs pulses feature 10⁻¹¹ temporal contrast at -20 ps and a carrier-envelope-phase drift of 240 mrad root mean square.

Approaching the limits of carrier-envelope phase stability in a millijoule-class amplifier.

The demand for ever shorter light pulses presents a challenge to the detection and stabilization of the carrier-envelope phase (CEP) in amplifier systems. Here we present a combination of single-shot detection and a fast actuator that is capable of measuring and correcting the CEP in every single shot emitted by a millijoule-scale, multi-kHz femtosecond laser amplifier. The residual CEP noise within 50 s amounts to 98 mrad rms in-loop (fast detection, 5·105 shots) and 140 mrad out-of-loop (slow detection, 6250 shots), approaching the noise floor of the f-to-2f measurement. Both values represent a twofold improvement of the CEP stability over previously published results in comparable systems.

Personal experiences and attitudes towards intimate partner violence in healthcare providers in Guyana.

BACKGROUND: Intimate partner violence (IPV) is prevalent throughout the world and is a devastating public health problem. Healthcare workers (HCWs) are tasked with treating victims of IPV but may be victims themselves. Guyana is a lower-middle income country in South America. This study sought to determine the knowledge and attitudes of Guyanese HCWs and their perceived barriers to providing care in addition to determining the prevalence of IPV victimization and perpetration among HCWs. METHODS: HCWs at the only tertiary care hospital in the Guyana completed an anonymous survey that comprised 30 questions relating to IPV. RESULTS: The survey was completed by 87.5% of eligible HCWs. Of the respondents, 81.8% were female, 49.9% had ever experienced abuse and 21% admitted to perpetrating violence. Multivariate analysis found that the age groups 31-40 years (OR 2.3, 95% CI 1.1-4.6) and 41-50 years (OR 2.3, 95% CI 1.2-4.7) had higher odds of accepting justification for physical violence, and so did nursing staff (OR 4.3, 95% CI 1.4-13.1). Overall, 29.9% of HCWs accepted justification for physical violence in at least one of the named scenarios. CONCLUSION: This study demonstrates a high prevalence of IPV among HCWs and identifies prevailing attitudes regarding IPV. This knowledge is essential in developing effective, appropriate training programs and identifies a need to address IPV among the healthcare workforce.