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Nonlinear optical phenomena in semiconductors present several fundamental problems in modern optics that are of great importance for the development of optoelectronic devices. In particular, the details of photo-induced lattice dynamics at early time-scales prior to carrier recombination remain poorly understood. We demonstrate the first integrated measurements of both optical and structural, material-dependent quantities while also inferring the bulk impulsive strain profile by using high spatial-resolution time-resolved x-ray scattering (TRXS) on bulk crystalline gallium arsenide. Our findings reveal distinctive laser-fluence dependent crystal lattice responses, which are not described by previous TRXS experiments or models. The initial linear expansion of the crystal upon laser excitation stagnates at a laser fluence corresponding to the saturation of the free carrier density before resuming expansion in a third regime at higher fluences where two-photon absorption becomes dominant. Our interpretations of the lattice dynamics as nonlinear optical effects are confirmed by numerical simulations and by additional measurements in an n-type semiconductor that allows higher-order nonlinear optical processes to be directly observed as modulations of x-ray diffraction lineshapes.

Counseling services are only likely to be effective if individuals are willing to seek help. Although much of the research on youth help-seeking has focused on adolescents, few studies have examined this in regard to children. Constant comparison analysis of focus group discussions revealed differences based on age and gender. Knowledge, sources of help, willingness, concerns regarding confidentiality, levels of interpersonal openness and stigma tolerance differed based on age. Gender differences were also highlighted. Implications focus on enhancing help-seeking among youth.

Background Stigma about mental health is a significant problem in Jamaica and the wider English-speaking Caribbean. In general, negative attitudes and opinions about mental illness have been found to negatively impact psychological help-seeking among several populations.