We explore strategies for optimizing selectivity, specificity, and sensitivity in broadband CARS by precalculating
pulse shapes using an evolutionary algorithm. We show the possibility of selective excitation of a single constituent
in a test case of a mixture of five resonant compounds. The obtainable contrast ratio for a test case
of PMMA in a mixture of five resonant compounds is predicted to be 2000:1, and is related the uniqueness of
the complex vibrational response of the compound of interest compared to that of the surrounding molecules.
Furthermore we investigate how the effects of homodyne mixing in the focal volume affect the obtainable contrast
ratio and how noise affects the optimization. We also show preliminary results of experimental optimization of
the CARS signal from PMMA microspheres, resulting in high contrast imaging, free of non-resonant background
Photodynamic therapy (PDT) is a treatment based on the interaction of light, photosensitizing agents and tissue oxygen.
The light delivery in PDT is usually optimized by controlling the intensity, the spectrum, and/or the dosage of excitation
light. In this paper, we introduce a novel method that aims to improve the efficiency of PDT by controlling the <i>phase</i> of
the excitation light, an important and so far neglected parameter. This coherent control approach utilizes the coherence
properties of light-matter interaction and aims to manipulate the quantum interferences between various available
reaction pathways. In general, an outcome of a photochemical reaction can be optimized by enhancing the desired
reaction pathways and suppressing other unwanted pathways. Such optimizations can be done by appropriate tailoring of
the electric field profile of a broadband coherent excitation light, i.e. ultrafast laser pulse. Here, we used a femtosecond
laser source with adaptive pulse shaping together with a molecular feedback in a learning loop to search for and
synthesize such 'smart' laser pulses. Our control objective is to enhance the triplet yield of a model photosensitizer zinc
phthalocyanine (ZnPc), which then leads to enhancement of the overall PDT process. We use two coherent control
schemes where we optimize the ratio between the excited singlet state (S) and triplet state (T) ZnPc molecules both ways
(S/T and T/S). We demonstrate a control of 15% over the triplet yield between the found best and the worst pulse shapes.
Our preliminary results show that phase shaping can indeed be used in manipulating photosensitizer photophysics and
correspondingly the yield of singlet oxygen.
Chirality is an excellent indicator of life, but naturally occurring terrestrial and extra-terrestrial
samples nearly always exhibit massive depolarizing light scattering (DLS). This problem bears a
striking resemblance to that of developing a chirality-based non-invasive glucose monitor for diabetics.
Both applications require a lightweight, compact, efficient, and robust polarimeter that can operate
despite significant DLS. So for astrobiological applications, we developed a polarimeter that was
inspired from a polarimetry technique previously investigated for non-invasive in-vivo glucose-sensing.
Our polarimeter involves continuously rotating the plane of linear polarization of a laser beam to probe
a sample with DLS, and analyzing its transmission with a fixed analyzer to obtain a sinusoidal voltage
signal. We lock-in detect this signal using a reference signal from an analogous set up without any
sample. With milk as a scatterer, we find that this polarimeter detects chirality in the presence of three
orders of magnitude more DLS than conventional polarimeters. It can accurately measure 0.1° of
polarization rotation in the presence of 15% milk.
We show that femtosecond optical pulses at optical communication wavelengths can be used for real time dispersion measurement of photonic crystal waveguides. Spectral resolutions on the order of one nanometer and bandwidths as large as tens of nanometers are demonstrated in real time measurements. Preliminary results are shown and discussed.
We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors
forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into
superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the
extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and
obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is
while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to
nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis
for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also
present some examples and discuss the results.
We show that simultaneous perturbation of periodicity and radius of air holes next to the guiding region in a photonic
crystal waveguide results in low loss and large bandwidth waveguides that are also single mode. We also show the
results of a single shot spectral phase measurement that can be used for real time dispersion measurement of photonic
A method for controlling the dispersion and thus group velocity of guided modes in photonic crystal (PC) waveguides using bi- and quasi-periodic lattices is presented. Rectangular lattice photonic crystals are proposed as possible candidates for implementing such control. However, these structures, and generally all bi-periodic lattices, develop undesirable characteristics as the perfect square lattice is perturbed. Thus, quasi-periodic photonic crystals, which have been shown to be promising in selective mode engineering, were examined next. A possible scheme for engineering of a single mode PC waveguide with guiding through the entire bandgap is presented.