Boosting few-cycle soliton self-frequency shift using negative prechirp.

Soliton self-frequency shifting of light pulses in fibers is used for versatile tunable light sources. Few-cycle pulses of high soliton number offer unique advantages, in particular the rate of Raman frequency shift is extremely fast. However, their dynamics is complicated, which makes the optimization of the frequency shifting difficult and sometimes counter-intuitive. We performed a systematic experimental study of the effects of initial prechirp for different pulse energies (for two different fibers). We found that a negative prechirp around C=-0.75 is the most effective (C being the chirp parameter). With such prechirping we managed to cross the severe OH absorption bands of nonlinear photonic crystal fibers. The mechanism behind the effectiveness of the prechirp appears to be the power distribution between the products of soliton fission.

Observation of Stimulated Hawking Radiation in an Optical Analogue.

The theory of Hawking radiation can be tested in laboratory analogues of black holes. We use light pulses in nonlinear fiber optics to establish artificial event horizons. Each pulse generates a moving perturbation of the refractive index via the Kerr effect. Probe light perceives this as an event horizon when its group velocity, slowed down by the perturbation, matches the speed of the pulse. We have observed in our experiment that the probe stimulates Hawking radiation, which occurs in a regime of extreme nonlinear fiber optics where positive and negative frequencies mix.

Comment on "Measurement of the phase refractive index of a photonic crystal fiber mode".

In a recent Letter [Opt. Lett.43, 2571 (2018)OPLEDP0146-959210.1364/OL.43.002571], Vengelis et al. have claimed to implement a new experimental technique for measuring the phase refractive index of a photonic crystal fiber mode. Unfortunately, while the experimental effort is appreciated, one of the key assumptions was inaccurate. Taking this error into account reveals that the measured value was the fiber's group index, rather than its phase refractive index.

When to say when: responding to a suicide attempt in the acute care setting.

Attempted suicide represents a personal tragedy for the patient and their loved ones and can be a challenge for acute care physicians. Medical professionals generally view it as their obligation to aggressively treat patients who are critically ill after a suicide attempt, on the presumption that a suicidal patient lacks decision making capacity from severe psychiatric impairment. However, physicians may be confronted by deliberative patient statements, advanced directives or surrogate decision makers who urge the withholding or withdrawal of life sustaining treatments based on the patient's underlying medical condition or life experience. How acute care providers weigh these expressions of patient wishes versus their own views of beneficence, non-maleficence and professional integrity poses a significant ethical challenge. This article presents a case that exemplifies the medical and ethical tensions that can arise in treating a patient following a suicide attempt and how to approach their resolution.

The challenge of post-implementation surveillance for novel meningococcal vaccines.

Novel serogroup B meningococcal vaccines are currently in late stage development and may be used in mass immunisation campaigns over the coming years. This represents an exciting development in the prevention of childhood meningitis, however monitoring the impact of these vaccines on meningococcal disease epidemiology will provide significant challenges. Although designed to prevent serogroup B meningococcal disease the vaccine antigens are not serogroup specific, creating the potential for multiple definitions of vaccine effectiveness and vaccine failure.