White light supercontinuum, which is generated by coupling short laser pulses into a nonlinear photonic
crystal fiber, not only covers an extremely broad wavelength range (e.g., from visible to near infrared) but
also has high spatial coherence. As a result, tightly focused supercontinuum can be used to trap a single
particle and simultaneously to perform broad-band ultra-sensitive optical spectroscopy at a single particle
level. In this paper we investigate the optical scattering spectroscopy of a single particle in white light
supercontinuum optical tweezers. Lorenz-Mie theory and Fourier angular spectrum analysis are used to
model the scattering of tightly focused supercontinuum by a uniform spherical scatterer. In addition, Born
approximation method is applied to analyze scattering by non-spherical weak scatterers. Unlike
conventional ensemble averaged spectroscopy, single particle spectroscopy has the unique capability to
probe the properties of individual particles, which can lead to many important applications such as ultrasensitive
sensing and nanoparticle characterization.
In this paper, we will present our preliminary results on our development of infrared and terahertz generation by ultrafast laser pulses. The objective of this project is to develop (i) portable and cost effective spatially coherent broadband Infrared (IR) and Terahertz (THz) illuminating light sources. To effectively generate spatially coherent broadband IR and THz sources, we use a novel nonlinear optical technical approach by harnessing the huge nonlinear effect of the specially designed and fabricated photonic crystal fibers (PCF). The major merits of these unique light sources are: (1) broad band (covering a wide range of spectroscopic signatures), (2) spatially coherent (so that beams can be delivered to the far distance like laser beams), (3) compact, portable and small footprint (all fiber design), (4) cost effective (traditional approaches such as cascaded laser systems are complicated and expensive for covering broadband).
We investigate lateral and axial chromatic confocal microscopy using supercontinuum white light, and its application to surface profile measurement. In the systems that we describe here, the lateral or the axial scanning is effectively realized by focusing different wavelengths of the supercontinuum to either different lateral or axial positions through purposely introduced chromatic dispersion and aberration respectively. As a result, the imaging speed can be greatly improved. We use this system to demonstrate the surface profile measurement of a microcircuit chip, with a sensitivity of 8.5 nm and a depth measurement range of about 7 microns.