Supercontinuum imaging and spectroscopy

Developing new optical imaging and spectroscopy techniques based on supercontinuum (SC) light sources is the major theme of this thesis. As a complex nonlinear optical phenomenon, SC generated in highly nonlinear photonic crystal fiber (PCF) exhibits broad spectral bandwidth (∼1000nm) and laser-like spatial coherence. These novel properties open new opportunities for imaging and spectroscopy applications. More specifically, as fast data acquisition rate has always been desired in three-dimensional optical imaging system, optical imaging part of this thesis discusses new methods of improving imaging scanning speed in both confocal and two-photon excitation fluorescence imaging systems by using wavelength division multiplexing (WDM) technique under the illumination of supercontinuum and femto-second laser sources. In spectroscopy part, we focus on broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy with SC light source. The high spatial coherence of SC enables the capability to optically trap microscopic objects while the broad bandwidth allow us to perform broad-band CARS measurement over a range up to 3000 cm-1. We also developed a technique to suppress non-resonant background, which is the major factor limiting the sensitivity of a CARS measurement. The first chapter gives the overview. Chapter three and four discuss imaging applications including reflection-type confocal microscopy and two-photon excitation fluorescence imaging. Chapter five discusses the topic of CARS and technique to suppress non-resonant background.;Chapter three focuses on the topic of WDM confocal microscopy by using broadband SC light source. Both lateral and axial WDM systems are investigated, which can potentially speed up the data acquisition rate significantly.;Chapter four describes WDM scanning for two-photon excitation fluorescence imaging system. It is experimentally demonstrated that the mechanical scanning along axial direction in two-photon imaging system can be replaced by tuning the incident laser wavelengths. A lateral WDM scanning also is demonstrated.;In chapter five, CARS spectroscopy is discussed. Broad band (up to 3000cm -1) CARS spectroscopy in supercontinuum trap is demonstrated. Non-resonant background can be suppressed by applying a polarization discriminated and time-resolved technique. A spectrally smoothed SC source is also investigated to obtain a smoothed-out non-resonant background so that the resonant Raman peaks can be easily observed.;In chapter two, I include a review of SC generation as well as a brief description on SC generation in PCF. SC generated in imaging fiber taper and spectrally smoothed SC generated by modulated femto-second pulses are also reported in this chapter. Generalized nonlinear Schrodinger equation (GNLS) is numerically solved for theoretical modeling of SC generation in PCF.