The concentration of atmospheric oxygen is measured over a 540-m path using supercontinuum absorption spectroscopy. The absorption data compared favorably with MODTRAN™ 5 simulations of the spectra after adjusting for the differences of index of refraction of air and matching the instrument spectral resolution, as described by the effective slit width. Good agreement with the expected atmospheric oxygen concentration is obtained using a previously developed multiwavelength maximum likelihood estimation inversion algorithm. This study demonstrates the use of the SAS technique for measuring concentrations of chemical species with fine absorption structure on long-atmospheric paths.
We investigate Raman spectroscopic sensing using whispering gallery microresonators as a label-free method toward single particle detection. Whispering gallery mode microresonators are used as platforms to perform sensitive particle detection by exploiting the strong, evanescent field of a resonant mode exposed on the surface
of the microresonator. Particles adhered to the microresonator surface interact with the field and scatter photons circulating within the resonator. In particular, Raman scattered photons are detected, providing
molecular-specific "fingerprint" information regarding the adhered particles. The exploitation of a resonant mode allows for enhancement of generated Raman signal over traditional methods of spontaneous Raman scattering. Preliminary proof-of-concept experimental results are shown.
Recently, we have demonstrated a hybrid diffractive optical element that combines the dispersion function of a grating
and the focusing function of a Fresnel lens (G-Fresnel) into a single device. The G-Fresnel promises a low f-number
enabling miniaturization of a spectrometer system while maintaining high spectral resolution. A proof-of-concept G-Fresnel
based spectrometer is demonstrated, yielding sub-nanometer resolution. Due to its compactness and low-cost
fabrication technique, the G-Fresnel based spectrometer has the potential for use in mobile platforms such as lab-on-a-chip
microfluidic devices and other mobile spectrometer applications.
Extending our developments of a previously reported supercontinuum lidar system has increased the capability for
measuring long path atmospheric concentrations. The multi-wavelength capability of the supercontinuum laser source
has the advantage of obtaining multiple line differential absorption spectra measurements to determine the
concentrations of various atmospheric constituents. Simulation software such as MODTRANTM 5 has provided the
means to compare and evaluate the experimental measurements. Improvements to the nanosecond supercontinuum laser
fiber coupled transceiver system have allowed open atmospheric path lengths greater than 800 m. Analysis of
supercontinuum absorption spectroscopy and measurements utilizing the updated system are presented.
A multi-wavelength, multi-static lidar has been designed and is being tested for the characterization of atmospheric
aerosols. This design builds upon multi-static lidar, multiple scattering analyses, and supercontinuum DIAL experiments
that have previously been developed at Penn State University. Scattering measurements at two polarizations are
recorded over a range of angles using CCD imagers. Measurements are made using three discrete visible wavelength
lasers as the lidar sources, or using a supercontinuum source with a wavelength range spanning the visible and near-IR
wavelengths. The polarization ratios of the scattering phase functions are calculated for multiple wavelengths to analyze
and determine the aerosol properties of artificially generated fog.