Ultrabroadband flying-focus using an axiparabola-echelon pair.

Flying-focus pulses promise to revolutionize laser-driven secondary sources by decoupling the trajectory of the peak intensity from the native group velocity of the medium over distances much longer than a Rayleigh range. Previous demonstrations of the flying focus have either produced an uncontrolled trajectory or a trajectory that is engineered using chromatic methods that limit the duration of the peak intensity to picosecond scales. Here we demonstrate a controllable ultrabroadband flying focus using a nearly achromatic axiparabola-echelon pair. Spectral interferometry using an ultrabroadband superluminescent diode was used to measure designed super- and subluminal flying-focus trajectories and the effective temporal pulse duration as inferred from the measured spectral phase. The measurements demonstrate that a nearly transform- and diffraction-limited moving focus can be created over a centimeter-scale-an extended focal region more than 50 Rayleigh ranges in length. This ultrabroadband flying-focus and the novel axiparabola-echelon configuration used to produce it are ideally suited for applications and scalable to >100 TW peak powers.

Programmable-trajectory ultrafast flying focus pulses.

"Flying focus" techniques produce laser pulses with dynamic focal points that travel distances much greater than a Rayleigh length. The implementation of these techniques in laser-based applications requires the design of optical configurations that can both extend the focal range and structure the radial group delay. This article describes a method for designing optical configurations that produce ultrashort flying focus pulses with programmable-trajectory focal points. The method is illustrated by several examples that employ an axiparabola for extending the focal range and either a reflective echelon or a deformable mirror-spatial light modulator pair for structuring the radial group delay. The latter configuration enables rapid exploration and optimization of flying foci, which could be ideal for experiments.

Control of the nonlinear response of bulk GaAs induced by long-wavelength infrared pulses.

The nonlinear optical response of GaAs is studied using extremely nonresonant 10 µm laser pulses with peak intensities greater than 2 GW/cm 2. We observe over an order of magnitude enhancement in the four-wave mixing efficiency by decreasing the CO 2 laser beat-wave frequency. This enhancement is attributed to currents of photoexcited unbound carriers modulated at the beat frequency, confirmed by measurements of nonlinear absorption at this long wavelength as well as a fully microscopic analysis of the excitation dynamics. Modeling of such nonperturbative semiconductor-laser interactions predicts that further decreasing the beat frequency can increase the nonlinear response and allow for its control over two orders of magnitude.

Multi-atmosphere picosecond CO2 amplifier optically pumped at 4.3 µm.

The possibility of the amplification of picosecond 10 µm pulses to gigawatt powers in an optically pumped 20 atmosphere CO2 laser is shown using numerical simulations. Multi-millijoule 4.3 µm pulses generated by a tunable Fe:ZnSe laser are considered for pumping.

Long-wave infrared picosecond parametric amplifier based on Raman shifter technology.

A new method for a long-wave infrared (LWIR), picosecond difference frequency generation (DFG) source using one near-infrared laser and a Raman shifter is experimentally tested and characterized. The signal seed for DFG is a Stokes pulse generated via transient stimulated Raman scattering in a nonlinear medium with a Raman frequency in the 2-20 µm range. A study of the dynamics of the transient Raman regime in liquid C6D6 has shown that the efficiency of Stokes production can be increased and the central wavelength can be controlled by chirping the pump pulse in order to compensate for chirping caused by self-phase modulation. High energy, ≥3 µJ, picosecond pulses at 10.6 µm have been generated in a GaSe crystal pumped by 1 mJ pulses of 1060 nm light from a Nd:glass laser.

Measurements of the nonlinear refractive index of air, N2, and O2 at 10 µm using four-wave mixing.

We report on measurements of the nonlinear index of refraction of air, N2, and O2 at a wavelength close to 10 µm by collinear four-wave mixing of a 200 MW CO2 laser beat-wave. The use of a 200 ps long beat-wave comprising radiation amplified on the 10P20 and 10R16 lines of the CO2 laser provides a sensitive method to measure the small nonlinearities characteristic of the gas phase in a spectral region where no such data exists.

High-power, mid-infrared, picosecond pulses generated by compression of a CO2 laser beat-wave in GaAs.

We report on the generation of a train of ∼2 ps, 10 µm laser pulses via multiple four-wave mixing and compression of an infrared laser beat-wave propagating in the negative group velocity dispersion region of bulk GaAs and a combination of GaAs and NaCl crystals. The use of a 200 ps, 106 GHz beat-wave, produced by combining laser pulses amplified on the 10P(20) and 10P(16) transition of a CO2 laser, provides a novel method for generating high-power, picosecond, mid-IR laser pulses at a high repetition rate. By using 165 and 882 GHz beat-waves, we show that cascaded phase-mismatched difference frequency generation plays a significant role in the four-wave mixing process in GaAs.

Supercontinuum generation from 2 to 20 µm in GaAs pumped by picosecond CO2 laser pulses.

We report on the generation of supercontinuum radiation from 2 to 20 µm in a 67 mm long GaAs crystal pumped by a train of 3 ps CO2 laser pulses. Temporal measurements indicate that sub-picosecond pulse splitting is involved in the production of such wide-bandwidth radiation in GaAs. The results show that the observed spectral broadening is heavily influenced by four-wave mixing and stimulated Raman scattering.

Amplification of multi-gigawatt 3 ps pulses in an atmospheric CO2 laser using ac Stark effect.

The 3 ps pulses are amplified to ~20 GW peak power in a TEA CO(2) laser using ac Stark broadening. Demonstration of such broadband coherent amplification of 10 µm pulses opens opportunities for a powerful mid-IR source at a high-repetition rate.

Work and productivity loss in the rizatriptan multiple attack study.

The objective of this study was to measure the self-reported effect of acute migraine and its treatment on paid work and productivity loss. Patients self-administered a questionnaire in which the impact of a recent migraine on paid work and productivity activities was assessed. We included the questionnaire in a randomized, double-blind, placebo-controlled, crossover, out-patient study designed to examine the safety and efficacy of rizatriptan (5-HT1B/1D receptor agonist) 10 mg p.o. in patients treating four separate migraine attacks. A total of 407 patients, aged 18-65 years, suffering from moderate to severe migrainous headaches was studied. Patients receiving rizatriptan compared with placebo reported 0.7 fewer hours (P < 0.01) of paid worked missed due to absenteeism, 0.4 fewer hours (P < 0.05) of productive time lost on the job, and 1.1 fewer total hours (P < 0.01) of work loss per migraine attack. Rizatriptan compared with placebo significantly reduced migraine-related work loss associated with absenteeism and decreased effectiveness on the job.

Duration of protection from clinical hepatitis A disease after vaccination with VAQTA.

Recent papers examining the expected persistence of anti-hepatitis A virus antibody following vaccination with inactivated hepatitis A vaccine have estimated that geometric mean antibody levels will remain above cut-off levels for 10-30 years. However, the methodology used in these papers did not take into account any estimates of variability between subjects. In this paper data from the persistence of antibody after the administration of another vaccine, VAQTA (hepatitis A vaccine, inactivated; MSD), were used to develop further models of antibody decay. Using individual subject estimates instead of group means allowed the estimation of time to negativity for various percentiles of the population (including the median), and the construction of confidence intervals on estimates of time to negativity. Data from studies of subjects who seroreverted to negativity, and subsequently received a booster dose, were also considered to show that subjects who lose detectable antibody are likely to remain protected from hepatitis A disease by persistent immune memory and rapid anamnestic response soon after exposure to hepatitis A virus. The estimates of duration of protection suggest that VAQTA will provide protection for many years, first through presence of antibody and further through an anamnestic response based on persistent immune memory.

Evaluation of a dressing to reduce nipple pain and improve nipple skin condition in breast-feeding women.

This study was designed to evaluate whether maintenance of a moist environment on the nipple skin during the first week of breast-feeding would improve damaged nipple skin condition, as indicated by the presence of eschar, erythema, and fissures, and reduce pain. Fifty White women applied a polyethylene film dressing with a perimeter adhesive system to a randomly determined nipple. The dressing was present at all times except during feeding. Subjects were assessed every 48 hours (four times) over 7 days. Serial photographic slides were obtained and assessed for skin characteristics. Nipple pain was self-rated with a verbal descriptor scale. Use of an occlusive film dressing on nipple skin during the first week of breast-feeding appeared to have limited influence on improvement in damaged skin condition. Summary scores indicated significant reduction in the amount of eschar on the surface of the nipple. There were no differences in erythema intensity or fissure severity. Use of a dressing significantly reduced nipple pain during the study period.

Skin changes and pain in the nipple during the 1st week of lactation.

OBJECTIVE: To document skin changes in the nipple during the 1st week of breastfeeding and to explore the relationship of such changes to pain. DESIGN: Longitudinal descriptive study. Subjects were visited four times during the 1st week of breastfeeding. SAMPLE: Convenience sample of 20 Caucasian women. SETTING: Hospital and home. MAIN OUTCOME MEASURES: Observed skin characteristics of the nipple included erythema, edema, fissures, blisters, inflamed areas, eschar, white patches, dark patches, yellow patches, peeling, pus, and ecchymosis. Subject-rated nipple pain. RESULTS: Skin changes were identified and quantified. Changes were visible in 100% (20) of the sample, and 65% (13) had severe skin damage; 90% (18) of the subjects reported pain. Some correlations between skin characteristics and pain were statistically significant, but not clinically meaningful. Skin damage was concentrated on the tip of the nipple. CONCLUSIONS: The data chronicle skin changes and their relationship to nipple pain during the 1st week of breastfeeding. Normal neonatal sucking appears to induce a suction wound on the skin of the nipples of many breastfeeding women that may account for pain experienced at the onset of lactation.

A method of designing clinical trials for combination drugs.

Many pharmaceutical companies are now exploring combination drug therapies as an alternative to monotherapy. Consequently, it is of interest to investigate the simultaneous dose response relationship of two active drugs to select the lowest effective combination. In this paper, we propose a method for designing clinical trials for drug combinations that seems to offer several advantages over the 4 x 3 or even larger factorial studies that have been used to date. In addition, our proposed method provides a convenient formula for calculating the required sample size.

Changes in dyspnea-fatigue ratings as indicators of quality of life in the treatment of congestive heart failure.

A new clinical index of dyspnea and fatigue has been applied to rate the condition of patients with congestive heart failure. The index has 3 components, each rated on a scale from 0 to 4, for the magnitude of the task that evokes dyspnea or fatigue, the magnitude of the pace (or effort) with which the task is performed and the associated functional impairment in general activities. The ratings for each component are added to form an aggregated score, which can range from 0, for the worst condition, to 12, for the best. Because dyspnea and fatigue are prime symptoms and sources of clinical distress, the index helps reflect the quality of life in patients with congestive heart failure. In double-blind trials of therapy, changes in the index showed good correlations with patients' self-selected ratings of improvement. The posttherapeutic changes in the index ratings were significantly higher with a new active agent (lisinopril) than with placebo or another active agent (captopril).

Effet de phase dans la dispersion de la puissance lumineuse des fibres optiques unimodales.

Pulse broadening calculations in monomode fibers do not include till now the phase variation of the coherent input field. Although it is correct to ignore this variation at wavelengths different from the zero material dispersion wavelength lambda(o), this effect must be taken into account for wavelengths nearly equal to lambda(o). We have found for silica-type fibers that if the relative source linewidth (Deltalambda(o))/lambdao is less than 10(-3), the phase effect largely dominates over important distances in the evaluation of the pulse broadening giving rise to a decrease of the r.m.s. output pulse width. Therefore, this effect must be relevant for the estimation of the maximum information capacity on monomode fibers.