Perry S. Edwards

Demonstration of a PDMS based hybrid grating and Fresnel lens (G-Fresnel) device

A hybrid device that we term G-Fresnel (i.e., grating and Fresnel) is demonstrated. It fuses the functions of a grating and a Fresnel lens into a single device. We have fabricated the G-Fresnel device by using polydimethylsiloxane (PDMS) based soft lithography. Three-dimensional surface profilometry has been performed to examine the device quality. We have also conducted optical characterizations to confirm its dual focusing and dispersing properties. The G-Fresnel can be useful for the development of miniature optical spectrometers as well as emerging optofluidic applications.

Proposal and demonstration of a spectrometer using a diffractive optical element with dual dispersion and focusing functionality

We propose an optical spectrometer using a hybrid grating-Fresnel (G-Fresnel) diffractive optical element. Theoretical simulation shows that a spectral resolution of approximately 1 nm can be potentially achieved with a millimeter-sized G-Fresnel. A proof-of-concept G-Fresnel-based spectrometer with subnanometer spectral resolution is experimentally demonstrated. The proposed method provides a promising new way for realizing compact optical spectrometers.

Holographic coherent anti-Stokes Raman scattering bio-imaging.

CARS holography captures both the amplitude and the phase of a complex anti-Stokes field, and can perform three-dimensional imaging by digitally focusing onto different depths inside a specimen. The application of CARS holography for bio-imaging is demonstrated. It is shown that holographic CARS imaging of sub-cellular components in live HeLa cells can be achieved.

Measurement of atmospheric oxygen using long-path supercontinuum absorption spectroscopy

Abstract 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.

COHERENT ANTI-STOKES RAMAN SCATTERING HOLOGRAPHY: THEORY AND EXPERIMENT

We review coherent anti-Stokes Raman scattering (CARS) holography as a non-scanning, label-free, three-dimensional imaging technique. The theory of CARS and its integration with digital holography is explored. We then discuss the experimental implementations of CARS holography including in-line and off-axis modalities and the demonstrations of three-dimensional imaging, chemical selectivity and the application of CARS holography to biological imaging.

Smartphone based optical spectrometer for diffusive reflectance spectroscopic measurement of hemoglobin

We report a miniature, visible to near infrared G-Fresnel spectrometer that contains a complete spectrograph system, including the detection hardware and connects with a smartphone through a microUSB port for operational control. The smartphone spectrometer is able to achieve a resolution of ~5 nm in a wavelength range from 400 nm to 1000 nm. We further developed a diffuse reflectance spectroscopy system using the smartphone spectrometer and demonstrated the capability of hemoglobin measurement. Proof of concept studies of tissue phantoms yielded a mean error of 9.2% on hemoglobin concentration measurement, comparable to that obtained with a commercial benchtop spectrometer. The smartphone G-Fresnel spectrometer and the diffuse reflectance spectroscopy system can potentially enable new point-of-care opportunities, such as cancer screening.

Label-Free Particle Sensing by Fiber Taper-Based Raman Spectroscopy

A fiber taper-based method for label-free Raman sensing is presented, which exploits the interaction between adsorbed specimen and the exposed evanescence tail of guided pump light. Chemical specificity and detection of microsphere specimens with diameters as small as 1 μm m are shown. To improve the sensitivity, we further propose resonator-enhanced Raman spectroscopy by taking advantage of the power build-up of a resonant mode in a cavity. Proof of concept is demonstrated by incorporating a fiber taper within a fiber ring resonator and locking a tunable laser to a circulating resonant mode. This demonstration shows a modest 40% enhancement of the Raman signal.

Multi-wavelength multi-angular lidar for aerosol characterization

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.

A compact optical spectrometer based on a single-grating Fresnel diffractive optical element

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.

Supercontinuum laser sensing of atmospheric constituents

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.