Diffractive optical elements for pitchfork beam shaping

A set of laser beam shaping optics is designed by an iterative method using an adaptive additive algorithm to transform a Gaussian beam into a pitchfork beam. Two diffractive optical elements are designed based on Fresnel diffraction to reduce the amount of energy in the first-order diffraction ring and to increase the depth of focus for the optical system. These two beam properties are found to depend on the diameter of the desired beam and the Airy disk diameter. If the diameter of the desired beam is large, then the optical system yields better results in achieving the above-mentioned two beam properties. The performance of the diffractive optical elements is compared to a previous laser beam shaping system designed by the ray-tracing technique. A pinhole scanning power meter is used to measure the laser irradiance profile at the focal plane to verify the existence of the pitchfork beam. The irradiance profile measurement shows that diffractive optical elements allow better control for reducing the amount of energy in the diffraction side lobes

Partially coherent conical refraction promises new counter-intuitive phenomena

In this paper, we extend the paraxial conical refraction model to the case of the partially coherent light using the unified optical coherence theory. We demonstrate the decomposition of conical refraction correlation functions into well-known conical refraction coherent modes for a Gaussian Schell-model source. Assuming randomness of the electrical field phase of the input beam, we reformulated and significantly simplified the rigorous conical refraction theory. This approach allows us to consider the propagation of light through a conical refraction crystal in exactly the same way as in the classical case of coherent radiation. Having this in hand, we derive analytically the conical refraction intensity both in the focal plane and in the far field, which allows us to explain and rigorously justify earlier experimental findings and predict new phenomena. The last include the counterintuitive effect of narrowing of the conical refraction ring width, disappearance of the dark Poggendorff’s ring in the Lloyd’s plane, and shift of Raman spots for the low-coherent conical refraction light. We also demonstrate a universal power-law dependence of conical refraction cones coherence degree on the input correlation length and diffraction-free propagation of the low-coherent conical refraction light in the far field

Propagation-invariant waves in acoustic, optical, and radio-wave fields

The physical phenomena considered in this thesis are associated with electromagnetic and acoustic waves that propagate in free space or in homogeneous media without diffraction. The concept of rotationally periodic wave propagation is introduced in the first journal article included in the thesis and it is subsequently used to analyse waves that avoid diffractive deterioration by repeatedly returning to their initial shape, possibly rotated around the optical axis. Such waves constitute an essential generalisation to several kinds of acoustic and optical beams, such as Bessel beams and self-imaging waves. Additionally, rotationally periodic waves also comprise pulsed wave forms that may propagate with a velocity independent of the speed of light (or sound) in the particular medium. This does not, however, lead to any violation of relativistic principles, as the pulse is continuously reformed by signals that have synchronously been transmitted from different locations. The individual articles in this dissertation mainly concentrate on the properties of pulsed waves. Two specific issues are also treated in the dissertation: (i) Acoustic nondiffracting waves are considered in anisotropic, piezoelectric crystals. Their propagation may differ drastically from that of ordinary (plane) waves, and nondiffracting waves may also include effects such as internal diffraction, phonon focusing, and caustics. Possible transducer structures are considered for the generation of nondiffracting waves into bulk crystals. (ii) Generation of Bessel beams have also been verified with the use of radio holograms in the millimetre-wave regime. Hologram techniques developed have allowed the investigation of various other wave forms and their propagation, such as tapered plane waves and radio-wave vortices. A back-propagation algorithm has also been introduced for designing holograms that form wave fields of an arbitrary design.reviewe

Subsurface optical microscopy of semiconductor integrated circuits

Thesis (Ph.D.)--Boston UniversityThe semiconductor industry continues to scale integrated circuits (ICs) in accordance with Moore's Law, and is currently developing the processing infrastructure at the 14nm technology node and smaller. In the wake of such rapid progress, a number of challenges have arisen for the optical failure analysis methods to meet the requirements of the advancing process technology. Most notably, complex circuits with shrinking critical dimensions will demand higher resolution signal localization currently beyond the capability of the existing optical techniques. This dissertation aims to develop novel optical systems to address the challenges of non-destructive circuit diagnostics at the 14nm technology node and beyond. Backside imaging through the silicon substrate has become an industry standard due to the dense multi-level metal wiring and the packaging requirements. The solid immersion lens is a plano-convex lens placed on the planar silicon substrate to enhance the subsurface focusing and collection of light in back-side imaging of ICs. The silicon and gallium-arsenide aplanatic solid immersion lenses (aSILs) were investigated in detail for the subsurface laser-scanning, voltage modulation, photon emission and dark-field IC imaging applications. Wave-front sensing and shaping techniques were developed to evaluate and mitigate optical aberrations originating from practical issues. Furthermore, the method of pupil function tailoring was explored for sub-diffraction spatial resolution. Super-resolving annular phase and amplitude pupil masks were developed and experimentally implemented. A record-breaking light confinement of 0.02 λ2 0(λ 0 refers to the free-space wavelength) was demonstrated using the vortex beams. The beam invasiveness is a critical issue in the optical circuit probing as the localized heat due to the absorption of the focused beams may unwittingly interfere with the circuit operation in the course of a measurement. A dual-phase interferometry assisted circuit probing was developed to enhance the signal extraction sensitivity by as much as an order of magnitude. Thus, the power requirement of the probe beam is significantly reduced to avert the consequences of the beam invasiveness. The optical systems and methods developed in this dissertation were successfully demonstrated using a number of modern ICs including devices of 14nm, 22nm, 28nm and 32nm technology nodes

Focal Field Distributions for Cylindrical Vector Beams: anti-resolution

Ph.DDOCTOR OF PHILOSOPH

Optimal Phase Masks for High Contrast Imaging Applications

Phase-only optical elements can provide a number of important functions for high-contrast imaging. This thesis presents analytical and numerical optical design methods for accomplishing specific tasks, the most significant of which is the precise suppression of light from a distant point source. Instruments designed for this purpose are known as coronagraphs. Here, advanced coronagraph designs are presented that offer improved theoretical performance in comparison to the current state-of-the-art. Applications of these systems include the direct imaging and characterization of exoplanets and circumstellar disks with high sensitivity. Several new coronagraph designs are introduced and, in some cases, experimental support is provided. In addition, two novel high-contrast imaging applications are discussed: the measurement of sub-resolution information using coronagraphic optics and the protection of sensors from laser damage. The former is based on experimental measurements of the sensitivity of a coronagraph to source displacement. The latter discussion presents the current state of ongoing theoretical work. Beyond the mentioned applications, the main outcome of this thesis is a generalized theory for the design of optical systems with one of more phase masks that provide precise control of radiation over a large dynamic range, which is relevant in various high-contrast imaging scenarios. The optimal phase masks depend on the necessary tasks, the maximum number of optics, and application specific performance measures. The challenges and future prospects of this work are discussed in detail