Heeseong Jeong

Complete mapping of complex reflection coefficient of a surface using a scanning homodyne multiport interferometer

We present a novel multiport coherent optical detection scheme which can simultaneously measure phase and amplitude of a signal beam. Using a scanning interferometer arrangement, we were able to map local variations of magnitude and phase of the complex reflection coefficient of a surface or thin film. We will show that this scheme can be used not only for locating defects on the surface but also for identifying the nature of defects.

Actively stabilized optical feedback scheme for very stable, high sensitivity shear-force measurement

We present here an active feedback control scheme which can maintain the distance between a laterally vibrating tapered optical fiber tip (TOFT) and a one facet of a laser diode (LD) at optimum value to measure the vibration amplitude of the TOFT in an optical feedback shear-force measurement scheme. Extremely good sensitivity for measuring the vibration amplitude, 9.58×10−2 pm/√Hz for a metal coated TOFT, can be maintained for at least 6 h by use of an active stablization scheme. Using a linearized lasing model of the LD in the presence of optical feedback, we are able to determine the vibration amplitude and effective reflection coefficient of the TOFT.

Observations of vectorial effects in multiple filamentation using a near-field scanning optical microscope

Effect of the initial polarization state of an axially symmetric beam propagating through a self-focusing medium has been observed by the use of a near-field scanning optical microscope (NSOM). As predicted in the theory of vectorial effects, a circularly polarized beam is likely to suppress multiple filamentation (MF).