Here, we present our development of several experimental methods, which, when applied together, can provide a thorough characterization of the nonlinear refraction and absorption properties of materials. We focus mainly on time-resolved methods for studying both transient absorption and refraction that reveal molecular dynamics including excited-state absorption, singlet-triplet transfer, instantaneous electronic nonlinear refraction, and molecular reorientation. In particular, we will describe our recent studies of new materials including organometallic compounds and organic solvents such as Tetrachloroethylene (C2Cl4).
Tuberculosis is a highly contagious disease such that global latent patient can be as high as one third of the world population. Currently, latent tuberculosis was diagnosed by stimulating the T cells to produce the biomarker of tuberculosis, i.e., interferon-γ. In this paper, we developed a paraboloidal mirror enabled surface plasmon resonance (SPR) interferometer that has the potential to also integrate ellipsometry to analyze the antibody and antigen reactions. To examine the feasibility of developing a platform for cross calibrating the performance and detection limit of various bio-detection techniques, electrochemical impedance spectroscopy (EIS) method was also implemented onto a biochip that can be incorporated into this newly developed platform.
The microfluidic channel of the biochip was functionalized by coating the interferon-γ antibody so as to enhance the detection specificity. To facilitate the processing steps needed for using the biochip to detect various antigen of vastly different concentrations, a kinetic mount was also developed to guarantee the biochip re-positioning accuracy whenever the biochip was removed and placed back for another round of detection. With EIS being utilized, SPR was also adopted to observe the real-time signals on the computer in order to analyze the success of each biochip processing steps such as functionalization, wash, etc. Finally, the EIS results and the optical signals obtained from the newly developed optical detection platform was cross-calibrated. Preliminary experimental results demonstrate the accuracy and performance of SPR and EIS measurement done at the newly integrated platform.
Out of the many wavefront sensing techniques, Shack Hartmann wavefront sensor remains the most
popular and the most versatile. Its optical configuration utilized a micro-lens array to measure the
directivity of the light beam associated with each micro-lens. In this design, smaller size of micro-lens
leads to angular resolution improvement. However, smaller size micro-lens typically is associated to
shorter depth of focus, which makes it difficult to focus on sensor array properly. In addition, the size
of micro-lens array is limited by the diffraction limit. In today’s technology, micro-lens with
dimensions in size of a few hundred of microns is possible. This dimension posts the limitation of the
angular resolution possible for Shack Hartmann wavefront sensor. To alleviate the compromise
between the angular resolution and the depth of focus, a sub-wavelength annular aperture (SAA)
structure was developed to generate Bessel light beams. That is, the SAA performs similar functions as
that of the micro lens array in traditional wave front sensors. It is shown that this design maintains a
sub-wavelength focusing capability while achieves tens of micron depth of focus in the far-field region,
which leads to an improved wavefront sensor. Both simulation and experimental results are detailed.