We have measured the subpicosecond optical response of a solid‐state, semiconductor‐to‐metal phase transition excited by femtosecond laser pulses. We have determined the dynamic response of the complex refractive index of VO₂ thin films by making pump‐probe optical transmission and reflection measurements at 780 nm. The phase transition was found to be largely prompt with the optical properties of the high‐temperature metallic state being attained within 5 ps. The ultrafast change in complex refractive index enables ultrafast optical switching devices in VO₂.

We have measured the subpicosecond optical response of a solid‐state, semiconductor‐to‐metal phase transition excited by femtosecond laser pulses. We have determined the dynamic response of the complex refractive index of polycrystalline VO₂ thin‐films by making pump‐probe optical transmission and reflection measurements at 780 nm. The phase transition was found to be largely prompt with the optical properties very close to the high‐temperature metallic state being attained within about 5 ps. The equilibration of the metallic state after femtosecond excitation was modeled by non‐exponentially decaying perturbations in the metallic state electron density and collision frequency. The decay of both these plasma parameters was well fit by a 1/√t time dependence. This indicated that a diffusion process governed the equilibration of the metallic phase of VO₂.

The aim of this paper is to compare the properties of four different profiles which can be used as multifocal intraocular lens. The Hankel transform based on the theory of scalar diffraction is applied to a binary profile, a parabolic one, a parabolic profile with holes, and finally a sinusoidal one. This enables to study the various distributions of the diffractive efficiencies and the axial chromatism. The image quality is evaluated by means of simulations of the MTFs with Zemax®. Finally we propose a new way to graphically synthesize all the properties of these lenses, using a radar graph.

We demonstrate the application of a subpicosecond optical parametric amplifier working at degeneracy to imaging in diffuse media. This optical parametric amplifier exhibits small-signal gains greater than 10⁴, thereby acting as a high-gain ultrafast amplifying gate. We have used it to construct the image of a grid pattern hidden behind 20 mean free paths of a highly diffusing solution of latex microspheres with a spatial resolution of 200 μm.

Gabor-domain optical coherence microscopy (GD-OCM) was applied ex vivo in the investigation of corneal cells and their surrounding microstructures with particular attention to the corneal endothelium. Experiments using fresh pig eyeballs, excised human corneal buttons from patients with Fuchs’ endothelial dystrophy (FED), and healthy donor corneas were conducted. Results show in a large field of view ($1\mathrm{mm}\times 1\mathrm{mm}$) high definition images of the different cell types and their surrounding microstructures through the full corneal thickness at both the central and peripheral locations of porcine corneas. Particularly, an image of the endothelial cells lining the bottom of the cornea is highlighted. As compared to healthy human corneas, the corneas of individuals with FED show characteristic microstructural alterations of the Descemet’s membrane and increased size and number of keratocytes. The GD-OCM-based imaging system developed may constitute a novel tool for corneal imaging and disease diagnosis. Also, importantly, it may provide insights into the mechanism of corneal physiology and pathology, particularly in diseases of the corneal endothelium.

Five search algorithms from the literature of black-box optimization were implemented and applied to optical design problems. These algorithms are the Particle Swarm Optimization, Gravity Search Algorithm, Cuckoo Search, Covariance Matrix Adaptation Evolution Strategy and Nelder&Mead Simplex search. The performance of these search algorithms’ implementations was assessed using the BBOB2009 (Black Box Optimization Benchmark) benchmark suite. These algorithms were compared in the context of two optical case studies, one with conventional rotationally symmetric optics and one with freeform optics. A comparison was performed against a commercial optical design software. Finally we provided a simple restart scheme applicable in the workflow of an optical designer. To the best of our knowledge, this is the first in-depth quantitative comparison of optimization algorithms for optical design.