Adiabatic following model for two-photon transitions: Nonlinear mixing and pulse propagation

Two-photon resonantly enhanced parametric generation processes have generally been described using time-dependent perturbation theory. In this paper we show that a theory of two-photon coherent effects can be used to derive and explain these nonlinear mixing processes. Our technique makes use of the adiabatic following (AF) approximation to obtain solutions to a vector model describing the two-photon resonance. We show that the usual results for the nonlinear susceptibilities correspond to the r vector of Feynman, Vernon, and Hellwarth adiabatically following the gamma vector in the small-angle limit. Consequently, the theory allows a natural extension to large angles, and power-dependent nonlinear susceptibilities are obtained. We then use these AF results for the polarization to study the propagation of pulses nearly resonant with a two-photon transition, and we demonstrate that the pulse reshaping is due to the two related effects of a nonlinear pulse velocity and self-phase modulation.Peer reviewedElectrical and Computer Engineerin

Inventory of current EU paediatric vision and hearing screening programmes

Background: We examined the diversity in paediatric vision and hearing screening programmes in Europe. Methods: Themes relevant for comparison of screening programmes were derived from literature and used to compile three questionnaires on vision, hearing and public-health screening. Tests used, professions involved, age and frequency of testing seem to influence sensitivity, specificity and costs most. Questionnaires were sent to ophthalmologists, orthoptists, otolaryngologists and audiologists involved in paediatric screening in all EU fullmember, candidate and associate states. Answers were cross-checked. Results: Thirty-nine countries participated; 35 have a vision screening programme, 33 a nation-wide neonatal hearing screening programme. Visual acuity (VA) is measured in 35 countries, in 71% more than once. First measurement of VA varies from three to seven years of age, but is usually before the age of five. At age three and four picture charts, including Lea Hyvarinen are used most, in children over four Tumbling-E and Snellen. As first hearing screening test otoacoustic emission (OAE) is used most in healthy neonates, and auditory brainstem response (ABR) in premature newborns. The majority of hearing testing programmes are staged; children are referred after one to four abnormal tests. Vision screening is performed mostly by paediatricians, ophthalmologists or nurses. Funding is mostly by health insurance or state. Coverage was reported as >95% in half of countries, but reporting was often not first-hand. Conclusion: Largest differences were found in VA charts used (12), professions involved in vision screening (10), number of hearing screening tests before referral (1-4) and funding sources (8)

Comparison of self-administration and face-to-face interview for surveys of low back pain in adolescents

The aim of this study was to compare self-administration with face-to-face interview in the investigation of low back pain in adolescents. Fifty-seven adolescents with low back pain (mean age 17.3 y; range 16-18) first completed a questionnaire and were then invited to an interview. Analysis included item completion, percentages of agreement and weighted kappa. Item completion rates were high and comparable between self-administration and interview. Information between both methods was analogous for severity and localization of problems, sleep behaviour, medical consultation and sports/leisure activities. Onset, progression, duration of low back pain and some items on the influence of movement/positions presented less comparable data. Conclusion: Even when two different methods of data acquisition are used, results suggest that the method used does not change the interpretation of results in the case of most items