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We present a novel, interferometric, two-color, high-order harmonic generation setup based on a turn-key Ytterbium-doped femtosecond laser source and its second harmonic. Each interferometer arm contains a spatial light modulator with individual capabilities to manipulate the spatial beam profiles and to stabilize the relative delay between the fundamental and the second harmonic. In addition, separate control of the relative power and focusing geometries of the two color beams is implemented to conveniently perform automated scans of multiple parameters. A live diagnostics system gives continuous information during ongoing measurements.

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High-order harmonic generation (HHG) provides scalable sources of coherent extreme ultraviolet radiation with pulse duration down to the attosecond time scale. Efficient HHG requires the constructive interplay between microscopic and macroscopic effects in the generation volume, which can be achieved over a large range of experimental parameters from the driving field properties to those of the generating medium. Here, we present a systematic study of the harmonic yield as a function of gas pressure and medium length. Two regimes for optimum yield are identified, supporting the predictions of a recently proposed analytical model. Our observations are independent on the focusing geometry and, to a large extent, on the pulse duration and laser intensity, providing a versatile approach to HHG optimization.

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Shape resonances in physics and chemistry arise from the spatial confinement of a particle by a potential barrier. In molecular photoionization, these barriers prevent the electron from escaping instantaneously, so that nuclei may move and modify the potential, thereby affecting the ionization process. By using an attosecond two-color interferometric approach in combination with high spectral resolution, we have captured the changes induced by the nuclear motion on the centrifugal barrier that sustains the well-known shape resonance in valence-ionized N2. We show that despite the nuclear motion altering the bond length by only 2%, which leads to tiny changes in the potential barrier, the corresponding change in the ionization time can be as large as 200 attoseconds. This result poses limits to the concept of instantaneous electronic transitions in molecules, which is at the basis of the Franck-Condon principle of molecular spectroscopy.

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We demonstrate a novel dispersion-scan (d-scan) scheme for single-shot temporal characterization of ultrashort laser pulses. The novelty of this method relies on the use of a highly dispersive crystal featuring antiparallel nonlinear domains with a random distribution and size. This crystal, capable of generating a transverse second-harmonic signal, acts simultaneously as the dispersive element and the nonlinear medium of the d-scan device. The resulting in-line architecture makes the technique very simple and robust, allowing the acquisition of single-shot d-scan traces in real time. The retrieved pulses are in very good agreement with independent frequency-resolved optical grating measurements. We also apply the new single-shot d-scan to a terawatt-class laser equipped with a programmable pulse shaper, obtaining an excellent agreement between the applied and the d-scan retrieved dispersions.

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One of the most ubiquitous techniques within attosecond science is the so-called reconstruction of attosecond beating by interference of two-photon transitions (RABBIT). Originally proposed for the characterization of attosecond pulses, it has been successfully applied to the accurate determination of time delays in photoemission. Here, we examine in detail, using numerical simulations, the effect of the spatial and temporal properties of the light fields and of the experimental procedure on the accuracy of the method. This allows us to identify the necessary conditions to achieve the best temporal precision in RABBIT measurements. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

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Ultrafast processes in matter, such as the electron emission after light absorption, can now be studied using ultrashort light pulses of attosecond duration (10-18 seconds) in the extreme ultraviolet spectral range. The lack of spectral resolution due to the use of short light pulses has raised issues in the interpretation of the experimental results and the comparison with theoretical calculations. We determine photoionization time delays in neon atoms over a 40-electron volt energy range with an interferometric technique combining high temporal and spectral resolution. We spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations, thereby solving a puzzle raised by 7-year-old measurements.

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Electron dynamics induced by resonant absorption of light is of fundamental importance in nature and has been the subject of countless studies in many scientific areas. Above the ionization threshold of atomic or molecular systems, the presence of discrete states leads to autoionization, which is an interference between two quantum paths: direct ionization and excitation of the discrete state coupled to the continuum. Traditionally studied with synchrotron radiation, the probability for autoionization exhibits a universal Fano intensity profile as a function of excitation energy. However, without additional phase information, the full temporal dynamics cannot be recovered. Here we use tunable attosecond pulses combined with weak infrared radiation in an interferometric setup to measure not only the intensity but also the phase variation of the photoionization amplitude across an autoionization resonance in argon. The phase variation can be used as a fingerprint of the interactions between the discrete state and the ionization continua, indicating a new route towards monitoring electron correlations in time.

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We study the influence of the generation conditions on the group delay of attosecond pulses in high-order harmonic generation in gases. The group delay relative to the fundamental field is found to decrease with increasing gas pressure in the generation cell, reflecting a temporal walk-off due to the dispersive properties of the nonlinear medium. This effect is well reproduced using an on-axis phase-matching model of high-order harmonic generation in an absorbing gas.

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Photoinduced molecular processes start with the interaction of the instantaneous electric field of the incident light with the electronic degrees of freedom. This early attosecond electronic motion impacts the fate of the photoinduced reactions. We report the first observation of attosecond time scale electron dynamics in a series of small- and medium-sized neutral molecules (N(2), CO(2), and C(2)H(4)), monitoring time-dependent variations of the parent molecular ion yield in the ionization by an attosecond pulse, and thereby probing the time-dependent dipole induced by a moderately strong near-infrared laser field. This approach can be generalized to other molecular species and may be regarded as a first example of molecular attosecond Stark spectroscopy.

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High-order harmonic generation (HHG) in gases has been established as an important technique for the generation of coherent extreme ultraviolet (XUV) pulses at ultrashort time scales. Its main drawback, however, is the low conversion efficiency, setting limits for many applications, such as ultrafast coherent imaging, nonlinear processes in the XUV range, or seeded free electron lasers. Here we introduce a novel scheme based on using below-threshold harmonics, generated in a "seeding cell", to boost the HHG process in a "generation cell", placed further downstream in the focused laser beam. By modifying the fundamental driving field, these low-order harmonics alter the ionization step of the nonlinear HHG process. Our dual-cell scheme enhances the conversion efficiency of HHG, opening the path for the realization of robust intense attosecond XUV sources.

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An instrument for measuring carrier-envelope phase (CEP) drift of amplified femtosecond laser pulses at repetition rates up to the 100-kHz regime is presented. The device can be used for real-time pulse labeling and it could also enable single-loop CEP control of future high-repetition rate laser amplifiers. The scheme is demonstrated by measuring the CEP drift of a 1-kHz source.

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We investigate compression of ultrashort laser pulses by nonlinear propagation in gas-filled planar hollow waveguides, using (3+1)- dimensional numerical simulations. In this geometry, the laser beam is guided with a fixed size in one transverse dimension, generating significant spectral broadening, while it propagates freely in the other, allowing for energy up-scalability. In this respect the concept outperforms compression techniques based on hollow core fibers or filamentation. Small-scale self-focusing is a crucial consideration, which introduces mode deterioration and finally break-up in multiple filaments. The simulation results, which match well with initial experiments, provide important guidelines for scaling the few-cycle pulse generation to higher energies. Pulse compression down to few-cycle duration with energies up to 100 mJ levels should be possible.

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Cell surgery based on ultrashort laser pulses is a fast evolving field in biophotonics. Noninvasive intra cellular dissection at sub-diffraction resolution can be performed within vital cells with very little hazardous effects to adjacent cell organelles. Microscope objectives of high numerical aperture (NA) are used to focus ultrashort pulses to a small spot. Due to the high order of nonlinearity, plasma formation and thus material manipulation is limited to the very focus. Nonetheless nonlinear plasma formation is generally accompanied by a number of additional nonlinear effects like self-focusing and filamentation. These parasitic effects limit the achievable precision and reproducibility of applications. Experimentally it is known that the intensity of these effects decreases with increasing NA of the focusing optics, but the process of nonlinear plasma formation at high NA has not been studied numerically in detail yet. To simulate the interaction of ultrashort laser pulses with transparent materials at high NA a novel nonlinear Schr odinger equation is derived; the multiple rate equation (MRE) model is used to simultaneously calculate the generation of free electrons. Nonparaxial and vectorial effects are taken into account to accurately include tight focusing conditions. Parasitic effects are shown to get stronger and increasingly distortive for NA < 0.9, using water as a model substance for biological soft tissue and cellular constituents.

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The purpose of this study was to assess the suitability of various neurology patient education brochures, as well as neurology information on the World Wide Web, to determine whether they were appropriate for patients with low literacy. A convenience sample of 520 patients in university-based public and private neurology clinics participated. In this cross-sectional study, the patients' reading levels were assessed by using the Rapid Estimate of Adult Literacy in Medicine. Forty-three patient education materials were assessed for reading level by using the Fog Index and for suitability characteristics (including content, type and relevance of graphics, layout, type size and fonts, and motivating qualities) by using the Suitability Assessment of Materials. The mean education level of patients was 12th grade; however, the mean reading level was 7th-8th grade. Of the assessed materials, 91% were written at a 9th-grade level or above, even though only 58% of patients read at a 9th-grade level. Only 14% of the materials were considered to have superior suitability, whereas 58% were adequate, and 28% were determined not suitable. Thus, the available neurology patient education aids are not matched to the patient population or to the average U.S. reading levels. Ideally, information needs to be written at a 9th-grade level or below. Instructional graphics, simpler words, patient interaction, and cultural sensitivity improve material suitability.

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BACKGROUND: Smoking during pregnancy increases the health risks of the unborn child as well as the mother. Although smoking rates for the population as a whole have declined drastically in the past generation, since 1992 there has been an increase in smoking among women, teenagers, and adults living in poverty. The purpose of this study was to assess reading level, tobacco knowledge, attitudes, and practices of tobacco use among pregnant adult and adolescent women in the public health system in north Louisiana. METHODS: A convenience sample of 600 pregnant women was interviewed in person in the Obstetrics Clinics at Louisiana State University Health Sciences Center at Shreveport and E.A. Conway in Monroe. The structured interview contained detailed questions about smoking practices, tobacco knowledge, and attitudes. Reading was assessed using the Rapid Estimate of Adult Literacy in Medicine. Smoking practices were assessed by self-report and verified by measuring urine cotinine levels. The Cochran-Mantel-Haenszel test was used to estimate the relationship between reading level and knowledge and attitude; multiple logistic regression was used to determine which variable(s) predicted current smoking practices. RESULTS: Knowledge about the effects of smoking and concern about the health effect of smoking on their baby varied significantly by reading level, with participants with higher reading levels having more knowledge and greater concern. Smoking practices did not vary by reading level even when race, age, and living with a smoker were controlled. Race was a significant determinant of smoking practices, with more white women reporting currently smoking during pregnancy than African Americans (34% vs 8%). CONCLUSIONS: Reading level was related to knowledge about health effects of smoking. Women with higher reading levels were also more concerned about the adverse health effects of smoking on themselves and their babies. However, reading level was not correlated with smoking prevalence. The most significant determinant of smoking was race (with whites smoking significantly more than African Americans).

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UNLABELLED: Communication about childhood vaccine risks and benefits has been legally required in pediatric health care for over a decade. However, little is known about the actual practice of vaccine risk/benefit communication. OBJECTIVES: This study was conducted to identify current practices of childhood vaccine risk/benefit communication in private physician office settings nationally. Specifically, we wanted to determine what written materials were given, by whom, and when; what information providers thought parents wanted/needed to know, the content of nurse and doctor discussion with parents, and the time spent on discussion. We also wanted to quantify barriers to vaccine risk/benefit discussion and to prioritize materials and dissemination methods preferred as solutions to these barriers. METHODS: We conducted 32 focus groups in 6 cities, and then administered a 27-question cross-sectional mailed survey from March to September 1998, to a random national sample of physicians and their office nurses who immunize children in private practices. Eligible survey respondents were active fellows of the American Academy of Pediatrics or American Academy of Family Physicians in private practice who immunized children and a nurse from each physician's office. After 3 mailings, the response rate was 71%. RESULTS: Sixty-nine percent of pediatricians and 72% of family physicians self-reported their offices gave parents the Centers for Disease Control and Prevention Vaccine Information Statement, while 62% and 58%, respectively, gave it with every dose. In ~70% of immunization visits, physicians and nurses reported initiating discussion of the following: common side effects, when to call the clinic and the immunization schedule. However, physicians reported rarely initiating discussion regarding contraindications (<50%) and the National Vaccine Injury Compensation Program (<10%). Lack of time was considered the greatest barrier to vaccine risk/benefit communication. Nurses reported spending significantly more time discussing vaccines with parents than pediatricians or family physicians (mean: 3.89 vs 9.20 and 3.08 minutes, respectively). Both physicians and nurses indicated an additional 60 to 90 seconds was needed to optimally discuss immunization with parents under current conditions. Stratified analysis indicated nurses played a vital role in immunization delivery and risk/benefit communication. To improve vaccine risk/benefit communication, 80% of all providers recommended a preimmunization booklet for parents and approximately one half recommended a screening sheet for contraindications and poster for immunization reference. The learning method most highly endorsed by all providers was practical materials (80%). Other desirable learning methods varied significantly by provider type. CONCLUSIONS: There was a mismatch between the legal mandate for Vaccine Information Statement distribution and the actual practice in private office settings. The majority of providers reported discussing some aspect of vaccine communication but 40% indicated that they did not mention risks. Legal and professional guidelines for appropriate content and delivery of vaccine communication need to be clarified and to be made easily accessible for busy private practitioners. Efforts to improve risk/benefit communication in private practice should take into consideration the limited time available in an office well-infant visit and should be aimed at both the nurse and physician.

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BACKGROUND: Health care professionals often use written material or video recordings to teach their patients without knowing which is more effective for comprehension of the information. METHODS: Patients watched either an instructional videotape about sleep apnea or read a newly designed brochure, then responded to a structured questionnaire containing 11 knowledge-based questions and 1 open-ended question (requesting suggestions for improvement of the brochure or videotape). RESULTS: Mean reported educational level was grade 12, and mean reading level was between grade 7 and 8. Using video significantly improved only two areas of knowledge for low-level (below grade 8) readers: defining sleep apnea (66% vs 43%) and identifying what continuous positive airway pressure (CPAP) does for the patient (94% vs 78%). Patients requested material with more diverse cultural representation, more information on treatment and outcomes, and fewer polysyllabic words. CONCLUSIONS: Emphasis on diagnosis and treatment, explained using simple words, should be reflected in the content of patient education brochures or videos. Providing information by video alone may have limited benefits.

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PURPOSE: To investigate the relationship between inadequate literacy and violent behavior among adolescents. METHODS: This descriptive study involved a convenience sample of 386 adolescents who participated in a summer track and field and literacy program serving youths in low-income neighborhoods in Shreveport, Louisiana, during 1994-1996. Self-reported violence was measured using the Youth Risk Behavior Survey (YRBS) and reading grade levels were measured by the Slosson Oral Reading Test-Revised (SORT-R). RESULTS: Youths ranged in age from 11 to 18 years; 66% were male, and 86% were African-American. Forty-three percent of adolescents tested had below-grade reading levels (> or = 2 grades). Participants with below-grade reading skills had higher rates of self-reported violent behaviors compared with those reading at grade level. When gender, race, and age were controlled for, adolescents reading below grade level were significantly more likely to report carrying weapons [odds ratio (OR) = 1.9; 95% confidence interval (CI) 1.1-3.5], carrying guns (OR = 2.6; CI 1.1- 6.2), to have been in a physical fight at school (OR = 1.7; CI 1.1-2.6), and to have been in a physical fight resulting in injuries requiring treatment (OR = 3.1; CI 1.6-6.1). In addition, youths reading below grade level were significantly more likely to be threatened at school with a weapon (OR = 2.1; CI 1.2-3.7) and to report missing days of school in the previous 30 days because they felt unsafe at school (OR = 2.3; CI 1.3-4.3). In characterizing the violence related behaviors, we found that low reading-level adolescents were more likely to be both aggressor/perpetrator and victim (44% vs. 32%; p = .02) and less likely to be only a victim (6% vs. 12%; p = .04) compared to adolescents with grade-appropriate reading skills. CONCLUSIONS: Below-grade-level reading was significantly related to violence behaviors among adolescents who volunteered for a summer track and field program. Longitudinal studies are needed to further investigate the relationship of below-grade-level reading and aggressive/perpetrator and victim behaviors.

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OBJECTIVE: Sleep-disorders patients must be given information and health education they understand. The purpose of this study was twofold: (1) to assess suitability of American Sleep Disorders Association and National Sleep Foundation patient education brochures; and (2) to assess one widely used brochure, using patient input and patient literacy level, as a model for development of future materials. DESIGN: Twelve American Sleep Disorders Association and National Sleep Foundation brochures were assessed for reading level using Grammatik, and for design, presentation, and motivating qualities using the Suitability Assessment of Materials (SAM). Patient literacy level was assessed using the Rapid Estimate Of Adult Literacy in Medicine (REALM). SETTING: The Louisiana State University Medical Center sleep clinic, faculty private sleep clinic, and in the sleep center laboratory. PATIENTS OR PARTICIPANTS: During the months of February-May 1997, 170 sleep disorders patients, 39% African American, 59% white participated in the study. Participants ranged in age from 18-73 years, with a mean age of 46. MEASUREMENTS AND RESULTS: Suitability scores for the 12 brochures indicate that none scored in the superior range, 83% scored adequate, and 17% scored not suitable. Ninety-four percent of the brochures were written on a 12th grade level or higher, yet 37% of the sleep patients tested were reading at less than a 9th grade level. Low-level readers were significantly more likely than their higher-reading-level counterparts to report that a brochure was too long (22% vs 12%; p < .05), and that they would need help reading it (44% vs 3%; p < .001). CONCLUSIONS: Patients need sleep information given to them on a level they understand. When developing and selecting appropriate materials, reading level, length, and suitability of written material should be considered.

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OBJECTIVE: To study the effects of three approaches to increasing utilization of screening mammography in a public hospital setting in Northwest Louisiana. DESIGN: Randomized intervention study. POPULATION: Four hundred forty-five women aged 40 years and over, predominantly low-income and with low literacy skills, who had not had a mammogram in the preceding year. INTERVENTION: All interventions were chosen to motivate women to get a mammogram. Group 1 received a personal recommendation from one of the investigators. Group 2 received the recommendation plus an easy-to-read National Cancer Institute (NCI) brochure. Group 3 received the recommendation, the brochure, and a 12-minute interactive educational and motivational program, including a soap-opera-style video, developed in collaboration with women from the target population. MEASUREMENTS AND MAIN RESULTS: Mammography utilization was determined at 6 months and 2 years after intervention. A significant increase (p = .05) in mammography utilization was observed after the intervention designed in collaboration with patients (29%) as compared with recommendation alone (21%) or recommendation with brochure (18%) at 6 months. However, at 2 years the difference favoring the custom-made intervention was no longer significant. CONCLUSIONS: At 6 months there was at least a 30% increase in the mammography utilization rate in the group receiving the intervention designed in collaboration with patients as compared with those receiving the recommendation alone or recommendation with brochure. Giving patients an easy-to-read NCI brochure and a personal recommendation was no more effective than giving them a recommendation alone, suggesting that simply providing women in a public hospital with a low-literacy-level, culturally appropriate brochure is not sufficient to increase screening mammography rates. In a multivariate analysis, the only significant predictor of mammography use at 6 months was the custom-made intervention.

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