Physics and
Optical Engineering Faculty Projects
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.