Physics and Optical Engineering Faculty Projects

Feasibility of Lenticular Lenses for Use in Low-Cost/High-Power Laser Arrays

Alec _Sills

Professor Paul Leisher

Lenticular lenses are typically molded plastic optics which have found use in a variety of low-cost, large-area applications. For example, in lenticular printing, these lenses are applied to printed material such as postcards and posters to create the illusion of depth or to modify the image as the viewing angle is changed. The goal of this project is to assess the feasibility of this inexpensive, mass-produced technology in a high power laser array. Semiconductor vertical external cavity surface emitting lasers (VECSELs) arrays currently utilize expensive 2D optics arrays. These lenses are precision manufactured, and the cost can exceed the total of all the other components in the laser. It is not clear that the level of precision afforded by these optics is strictly necessary to achieve reasonable output from the semiconductor laser. If a VECSEL array utilizing a molded lenticular array could be demonstrated, it would represent a significant achievement in reducing the overall cost structure of this class of device.

Minor planet astrometry


Professor Richard Ditteon

The Harvard Smithsonian Center for Astrophysics is the home of the Minor Planet Center which keeps track of the locations of hundreds of thousands of minor planets in the solar system. Researchers use this information for dynamical studies of the solar system. For this project you will use images of minor planets taken for the minor planet photometry project (see below) to determine the precise location of these minor planets and report your observations to the Minor Planet Center. We also use this data in the Celestial Mechanics course (PH322) to calculate the minor planet orbit around the Sun to predict its future position.

Minor planet photometry

Professor Richard Ditteon

Minor planets are not usually spherical in shape. As they rotate about their own rotation axis, we will view larger or smaller sides of the minor planet and the minor planet will appear brighter or dimmer. We use the telescopes in the Oakley Observatory (on campus) and the Oakley Southern Sky Observatory (in Australia) to take images of minor planets over extended time periods. Measuring the brightness of the minor planet allows us to plot the variations and determine the rotation period of the minor planets. Observing the same minor planet at various positions in its orbit allows the determination the orientation of the rotation axis. A shape model for the minor planet can also be created.

Variable star photometry

Professor Richard Ditteon

Some kinds of stars oscillate. Their outer layers expand and cool and then contract and heat up. These changes cause changes in the amount of light the stars emit. Other stars are form binary pairs where one star passes in front of or behind the other star. We can monitor known variable stars to determine the amplitude and period of their oscillations and determine if they are intrinsic variables or eclipsing variables. We can also search star fields to discover new variable stars.

Search for supernovae

Professor Richard Ditteon

Supernovae occur when a star runs out of fuel and the star collapses in on itself creating a neutron star or a black hole. The supernova is actually due to the rebound of infalling material. During the rebound, the star can become nearly as bright as an entire galaxy of stars. Supernovae are used by astronomers to determine the distances to their host galaxies. But to make those distance measurements, astronomers need to know when and where a supernova is happening. In this project we would image dozens of distant galaxies in the hope of catching a supernova going off in one of them.

Nanoscience and Nanotechnology

Professor Renat Letfullin

Nano-Optics: Surface plasmon resonance phenomenon.  Surface plasmon resonance (SPR) has been investigated both for its fundamental importance and as a possible detection technique.  Recently, commercial biosensors have become available that rely on SPR for detecting various proteins and other DNA constituents.  With involved students we perform simulations of the integral and differential optical properties (such as scattering, absorption and attenuation cross sections and scattering amplitude functions) of nanoparticles below the diffraction limit for a broad range of the wavelengths of transverse electromagnetic waves.

Ultrashort laser radiation interaction with nanostructures. Two models will be studied to describe ultrashort laser pulse interactions with metal nanoparticles in time.  The first is a two-temperature model which involves fast thermalization within the electron subsystem, non-uniform energy transfer to the lattice, and electron energy losses due to electron heat transport into the particle volume.  The second is a one-temperature model based on a heat transfer equation written within a uniform heating approximation throughout the particle volume.  We perform the comparative simulations of temperature-time dynamics using these models for laser heating of metallic nanotargets in the femtosecond, picosecond and nanosecond regimes, thus providing an effective modeling method to explore the effects playing the determining role in the laser-matter interactions.

Laser-induced explosion of nanoparticles. The strongly-enhanced SPR of noble metal nanoparticles at optical frequencies makes them excellent scatters and absorbers of visible and near-IR light.  When the strongly-absorbing nanoparticles are irradiated by ultrashort laser pulses, their temperature rapidly reaches the thresholds for nonlinear effects and can cause an explosion of nanoparticles.  This involves the generation of a shock wave of dense vapors expanding in the cell volume with supersonic velocity, producing sound waves and optical plasma.  There are two main physical mechanisms that could lead to the laser-induced explosion of nanoparticles - (a) thermal explosion mode through electron-phonon excitation-relaxation and (b) Coulomb explosion mode through multiphoton ionization. We will estimate the threshold laser energy density required for the realization of the thermal explosion of nanoparticles.

Nanomedicine: New Dynamic Modes in Selective Cancer Nanomedicine

Professor Renat Letfullin

Microbubble overlapping mode. Bioconjugated nanoparticles are selectively attached to chosen cellular targets, in particular to membrane receptors activated by other antibodies.  When nanoparticles are irradiated by short laser pulses, they absorb the laser radiation, and their temperature rises very quickly, reaching the threshold of microbubble formation in the surrounding liquid medium. We study a new dynamic mode for selective cancer treatment that involves the overlapping of bubbles inside the cell volume. The nanobubble overlapping mode around intracellular structures induced by short laser pulses can dramatically increase the efficiency of the cancer treatment as a result of the larger damage range and higher expenditure rate in comparison to a thermal damage mode.

Nanoclusters aggregation mode. We propose a new mechanism for selective laser killing of abnormal cells by nanoclusters aggregated in the cell volume.  A cluster is a group of closely-located nanoparticles separated by the thickness of antibodies (10-30 nm), which has a typical size of 200-400 nm.  Here, the effective therapeutic effect for cancer cell killing is achieved due to a large damage area at the relatively-low energy density of the incident laser pulse.

Thermal explosion mode - nanobombs.  We propose yet another new mechanism for selective laser killing of abnormal cells by laser thermal explosion of single nanoparticles - nanobombs - delivered to the cells.  Thermal explosion of nanoparticles is realized when heat is generated within the strongly-absorbing target more rapidly than the heat can diffuse away.  Here, the effective therapeutic effect for cancer cell killing is achieved due to nonlinear phenomena, which accompany the thermal explosion of the nanoparticles:  generation of a strong shock wave with supersonic expansion of a dense vapor in the cell volume, producing sound waves and optical plasma.

Investigation of the optical properties of LEDs for lighting applications

Professor Robert M. Bunch

The use of light emitting diodes (LEDs) for lighting applications will continue to grow for many years. As new LED structures are developed, especially white light LEDs, there is a continuing need for methods to characterize their optical properties. The current project involves developing a test platform for LED measurements of the output spatial profile using precision rotational stages and calibrated detectors. Other projects will include measurements of total flux (optical power of an LED) using an integrating sphere and  spectral measurements to obtain color coordinates.

Polymer magnetism

Professor Maarij Syed

Magnetic properties of materials are both a fundamental discipline and a highly applied field with applications that range from imaging to data storage. In this project magnetism of unconventional composite material is investigated using a technique called Faraday Rotation (FR). FR refers to the phenomenon in which the axis of linearly polarized light is rotated as it propagates through a medium in a static magnetic field applied along the direction of propagation. The amount of rotation is proportional to the optical path length, and magnetic field strength, and a material-specific constant called the Verdet constant.  Materials with a large Verdet constant have applications as optical isolators, modulators, and magnetic field sensors, to name a few. However, despite the usefulness of FR, few studies have investigated this effect in the context of the nanoparticle composites. These composites refer to a general class of materials where a polymer matrix is seeded with magnetic nanoparticles. These systems allow for the investigation of magnetism at a nano scale where size dependent magnetic properties often result in interesting and novel departures from the well understood magnetic behavior of large scale bulk samples. The polymer matrix also modifies the behavior of these magnetic nano systems by making the observed properties a function of the chemical nature of the surrounding matrix, its mechanical rigidity which may aid or oppose magnetic alignment, etc. The project aims to explore all of these fascinating interrelationships by using different combinations of magnetic nanoparticles (Fe2O3, Fe3O4, etc.) along with various polymers (e.g., silicate gels, etc.). By employing FR to investigate these systems one can not only better understand nano magnetism, but it is also possible to investigate the application feasibility of these systems as optical isolators and magnetic field sensors.

Conventional application of FR is typically in DC mode, whereby the applied magnetic field is static. This project builds on the last two years of work where our lab has perfected a much more sensitive version of this technique that is referred to as the AC version of FR. The AC technique makes use of lock-in detection that allows for the reliable determination of exceedingly small rotation angles, which in turn can be used to precisely determine the Verdet constant of a given sample. To date, experiments involving the AC technique in our lab have used single wavelength sources. This project hopes to push the technique to a new level by using a broad band source and develop the related detection scheme, along with resolving noise issues that may be present in a new setup.

In short, the project represents an exciting blend of optics, electromagnetics, nano science, and experimental technique that would require the student pursuing the project to integrate all these interesting and challenging disciplines into his or her understanding.

Characterization of Student Produced Diodes

Professor Michael McInerney

A silicon diode is the end product of the laboratory in the course EP406 'Semiconductor Devices and Fabrication'.  Students actually make a wafer full of diodes as they learn the general methods of device fabrication.  Not all of the diodes on the wafer are successful.

The aim of this project is to characterize the diodes produced to determine why some are successful while others are not.  This characterization requires cutting, mounting and polishing specimens and observing under optical and electron microscopes.  An etch that is selective for different dopings of silicon must also be identified and used.

This project will help us improve the quality of the diodes that we make in EP406.

Electronics to show the device characteristics of a diode

Professor Michael McInerney

A simple diode conducts electricity in one direction and not in the opposite, reverse, direction.  It does have a tiny reverse current that can become large if the reverse bias exceeds a 'breakdown voltage'.  The forward current increases exponentially with bias until it saturates.  This behavior can be shown as a graph on an oscilloscope if you have the correct electronics.  This project is the design and production of these electronics.

The student doing this project will have to design and produce an electronic instrument that can take input from a signal generator and a diode and output the characteristic curve (I,V) for the diode to an oscilloscope.

This project will be a great help to PH405 and EP406.

Multiple pin-hole lens

Professor Michael McInerney

A pin hole is able to act as a lens but requires a bright light source.  Several pinholes can gather more light but their images interfere with each other.  This interference can be undone, or 'deconvolved' if the pattern of the pinholes is correct.  The aim of this project is to find a way to determine this correct pattern.  I suspect that a genetic search is a likely approach; but there may be others.

A pin-hole lens is useful for radiation that cannot be focussed easily; such as X-rays and gamma rays.

Our Sponsors: