Mon Thiri Myaing

Enhanced two-photon biosensing with double-clad photonic crystal fibers

A double-clad photonic crystal fiber was used to improve detection efficiency over a standard single-mode fiber in a two-photon fluorescence detection scheme in which the dye was excited and the fluorescence was detected back through the same fiber.

Biosensing based on two-photon fluorescence measurements through optical fibers.

We have performed two-photon fluorescence detection in a new scheme in which femtosecond laser pulses were delivered thorugh an optical fiber for nonlinear excitation and the emitted fluorescence was collected through the same fiber. Single-mode fibers were determined to give higher detection efficiency than multimode fibers, consistent with theoretical considerations. The utility of fiber-optic sensing based on two-photon fluorescence detection was proved by an experiment that measured the uptake of a targeted drug delivery agent into cultured cancer cells.

Gouy Phase Shift of Single-Cycle Picosecond Acoustic Pulses

Ultrafast laser pulses are used to generate single-cycle picosecond acoustic pulses in thin metal films on silicon. For small initial excitation spot sizes, propagation of the acoustic pulses across a 485mm Si crystal leads to significant diffraction effects. The temporal reshaping of the acoustic wave form due to diffraction is investigated, and we demonstrate that the acoustic far field can be reached.

Nonlinear propagation of negatively chirped pulses: Maximizing the peak intensity at the output of a fiber probe

A simple phenomenological scaling behavior is found for the power dependence of the pulse width for negatively pre-chirped pulses propagating in a normally dispersive fiber; the consequences for maximizing nonlinear signals such as two-photon fluorescence excited at the fiber output are considered.

Adaptive dispersion compensation for remote fiber delivery of near-infrared femtosecond pulses.

We report on remote delivery of 25-pJ broadband near-infrared femtosecond light pulses from a Ti:sapphire laser through 150 m of single-mode optical fiber. Pulse distortion caused by dispersion is overcome with precompensation by adaptive pulse shaping techniques, while nonlinearities are mitigated by use of an SF10 glass rod for the final stage of pulse compression. A near-transform-limited pulse duration of 130 fs was measured after the final compression.

Development of a double-clad photonic-crystal-fiber-based scanning microscope

Despite the fact that laser scanning confocal microscopy (LSCM) has become an important tool in modern biological laboratories, it is bulky, inflexible and has limited field of view, thus limiting its applications. To overcome these drawbacks, we report the development of a compact dual-clad photonic-crystal-fiber (DCPCF) based multiphoton scanning microscope. In this novel microscope, beam-scanning is achieved by directly scanning an optical fiber, in contrast to conventional beam scanning achieved by varying the incident angle of a laser beam at an objective entrance pupil. The fiber delivers femtosecond laser pulses for two-photon excitation and collects fluorescence back through the same fiber. Conventional fibers, either single-mode fiber (SMF) or multimode fiber (MMF), are not suitable for this detection configuration because of the low collection efficiency for a SMF and low excitation rate for a MMF. Our newly invented DCPCF allows one to optimize collection and excitation efficiency at the same time. In addition, when a gradient-index (GRIN) lens is used to focus the fiber output to a tight spot, the fluorescence signal collected back through the GRIN lens forms a large spot at the fiber tip because of the chromatic aberrations of the GRIN lens. This problem prevents a standard fiber from being applicable, but is completely overcome by the DCPCF. We demonstrate that this next generation scanning confocal microscope has an extremely simple structure and a number of unique features owing to its fundamentally different scanning mechanism: high flexibility, arbitrarily large scan range, aberration-free imaging, and low cost.

Double-clad photonic-crystal-fiber based scanning microscopy

We report the development of a novel double-clad photonic-crystal-fiber based multiphoton scanning microscope, which has a number of advantages over conventional scanning microscopes.

Two-photon fluorescence biosensing with conventional and photonic crystal fibers

Fluorescence is a powerful tool for biosensing, but conventional fluorescence measurements are limited because solid tumors are highly scattering media. To obtain quantitative in vivo fluorescence information from tumors, we have developed a two-photon optical fiber fluorescence (TPOFF) probe where excitation light is delivered and the two-photon fluorescence (TPF) excited at the tip of the fiber is collected back through the same fiber. In order to determine whether this system can provide quantitative information, we measured the fluorescence from a variety of systems including mouse tumors (both ex vivo and in vivo) which were transfected with the gene to express varying amounts of green fluorescence protein (GFP), and tumors which were labeled with targeted dendrimer-based drug delivery agents. The TPOFF technique showed results quantitatively in agreement with those from flow cytometry and confocal microscopy. In order to improve the sensitivity of our fiber probe, we developed a dual-clad photonic-crystal fiber which allowed single-mode excitation and multimode (high numerical aperture) collection of TPF. These experiments indicate that the TPOFF technique is highly promising for real-time, in vivo, quantitative fluorescence measurements.

Nonlinear propagation of negatively chirped pulses: maximizing the intensity at the output of a fiber probe

A simple phenomenological scaling behavior is found for the power dependence of the pulse width for negatively pre-chirped pulses propagating in a normally dispersive fiber; the consequences for maximizing nonlinear signals such as two-photon fluorescence excited at the fiber output are considered.