MultiPhoton SPatIal Frequency modulated Imaging (MP-SPIFI) has recently demonstrated the ability to simultaneously obtain super-resolved images in both coherent and incoherent scattering processes — namely, second harmonic generation and two-photon fluorescence, respectively.1 In our previous analysis, we considered image formation produced by the zero and first diffracted orders from the SPIFI modulator. However, the modulator is a binary amplitude mask, and therefore produces multiple diffracted orders. In this work, we extend our analysis to image formation in the presence of higher diffracted orders. We find that tuning the mask duty cycle offers a measure of control over the shape of super-resolved point spread functions in an MP-SPIFI microscope.
GaInP2 lattice-matched to GaAs or Ge plays an important role in state-of-the-art III-V multijunction solar cells. The fundamental band gap of constant-composition GaInP2 can be varied by as much as 100meV in metal-organic chemical vapor deposition (MOCVD) grown material by adjusting growth parameters that affect the degree of Cu-Pt ordering. These changes in the band gap of GaInP2 due to ordering can be exploited in the design of III-V solar cell devices. In order to accurately model the performance of these devices, accurate values of the optical constants of all layers are required. Previous literature reports of the optical properties of GaInP2 have primarily focused on highly disordered material or higher energy transitions in ordered material. While it has been noted that ordered GaInP2 material results in anisotropic optical properties, the bulk optical properties of GaInP2 as a function of ordering have not been sufficiently recorded in the literature for good optical modeling of III-V solar cell devices. In this paper, we present the dielectric functions for a range of ordered/disordered GaInP2 measured over the range 0.7-5.0 eV using spectroscopic ellipsometry. Data analysis of generalized ellipsometry data utilizing anisotropic multilayer models allows us to report accurate dielectric functions for both the ordinary and extraordinary optical axes.
An investigation of hot carrier relaxation in GaAs/AlxGa1-xAs multiple quantum wells and bulk GaAs in the high carrier density limit is presented. Two techniques have been employed: luminescence upconversion with < 80 fs temporal resolution has been used to cover the range from 100 fs to 100 ps, and time-correlated single-photon counting to cover the range from 100 ps to 2 ns. Electron temperatures as a function of time were determined from the slope of the high energy tail of the time-resolved photoluminescence spectra. Our results show that hot electron cooling rates in the quantum wells begin to become significantly slower than that in the bulk when the photogenerated carrier density is above a critical value of approximately 2 X 1018 cm-3; the difference in cooling rates increases rapidly with increasing carrier density. The time constant characterizing the power loss of hot carriers is also determined and discussed. A comparison is made with previous publications to resolve the confusion concerning the difference in cooling rates between quasi-2D and 3D systems.
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