Analysis on FM-to-AM conversion of SSD beam induced by etalon effect in a high-power laser system

FM-to-AM (frequency modulation-to-amplitude modulation) conversion caused by nonuniform spectral transmission of broadband beam is harmful to high-power laser facility. Smoothing by spectral dispersion (SSD) beam is a special broadband beam for its monochromatic feature at the given time and space on the near field. The traditional method which uses the optical spectral transfer function as filters cannot accurately describe its AM characteristics. This paper presents the theoretical analysis of the etalon effect for SSD beam. With a low-order approximation, the analytic model of the temporal shape of SSD beam is obtained for the first time, which gives the detailed AM characteristics at local and integral aspects, such as the variation of ripples width and amplitude in general situation. We also analyze the FM-to-AM conversion on the focal plane; in the focusing process, the lens simply acts as an integrator to smooth the AM of SSD beam. Because AM control is necessary for the near field to avoid optics damage and for the far field to ensure an optimal interaction of laser–target, our investigations could provide some important phenomena and rules for pulse shape control.

Terahertz Spectroscopy of Amorphous WSe2 and MoSe2 Thin Films

Time domain spectroscopy is used to determine the THz electromagnetic response of amorphous transition metal dichalcogenides WSe2 and MoSe2 in thin-film form. The dielectric function is obtained using a rigorous transmission model to account for the large etalon effect. The Drude–Smith model is applied to retrieve the dielectric function, and from there, the sample conductivity.

Photoreflectance and Resonant Raman Scattering in Short Period Si/Ge Superlattices on Ge (001) and Si (001)

ABSTRACTShort period Si/Ge superlattices have been grown on Ge (001) and Si (001) substrates by molecular beam epitaxy. The optical properties of the superlattices have been studied with photoreflectance. (PR) and resonant Raman scattering (RRS). With PR we are able to observe new, structural induced transitions for all superlattices which are related to E0-and E1-like gaps. The analysis of PR spectra is complicated by an optical etalon effect if the samples are sufficently thick. The E1-like transitions in the range between 1.9eV and 2.7eV are also studied with RRS. Due to the confinement of the optical phonons in the Ge and Si layers RRS is able to probe the bandstructure in each layer seperately. Localized electronic states in the Ge layers can be observed with RRS for a Si4Ge18 superlattice and are compared with PR measurements.