ECCS-0801412 S. Yun, Massachusetts General Hospital
Objective: The overall goal of this project is to understand and develop novel modelocking techniques in wavelength-swept lasers.
Intellectual merit: Sliding Frequency Modelocking (SFM) is a new technique for generating swept pulses using a unique mechanism to swept operation. A deeper understanding of SFM would greatly enhance our ability to develop a novel swept laser for new applications. This project aims to explore the fundamentals and technologies of SFM through theoretical and experimental investigations.
Broader Impacts: The proposed research promises to make important contributions to the fundamental understanding of swept laser technology and modelocking. It will provides the following: (1) improved theoretical models of modelocked swept lasers, (2) understanding and implementation of traditional modelocking techniques, such as active phase modulation and Kerr lens modelocking in swept lasers, and (3) novel picosecond swept lasers and high-speed Ti:sapphire swept lasers. Mode-locked swept lasers may enable a variety of applications ranging from nonlinear imaging to time-resolved spectroscopy. This project provides an ideal opportunity to educate and train graduate students and research fellows in the highly innovative and collaborative environment at Harvard Medical School. Undergraduate students enrolled in the Harvard-MIT HST summer institute and summer internship will participate in this project. Our group has extensive collaborations with other research groups as well as with industry. Mode-locked swept lasers have a significant potential to become a powerful light source to enable and facilitate a variety of applications, particularly in biomedical imaging to advance health care.
This project was an experimental study of a new method for producing laser pulses whose wavelength (color) change rapidly and repetitively in time. The range of the wavelength sweep is about 100 nm, centered at 1550 nm; this near-infrared wavelength range, which is invisible to the naked eye, coincides with the standard window in fiber-optic telecommunications and is a useful range for biomedical applications. An objective of the project was to understand and develop a mode locking technique the Principal Investigator of the project has recently discovered. The technique, termed sliding frequency modelocking or SFM, can generate color-changing laser pulses without using conventional modelocking principles. Uniquely, SFM originates from the swept filter employed in the laser cavity -- therefore it is a fundamental property of any wavelength-swept lasers. The SFM pulse generated from a fiber laser has typically a pulsewidth of about 10 picoseconds (light can travel by only 3 mm in this period). The laser demonstrated is capable of changing the wavelength over 100 nm in just 1 millisecond. The results of this project allow laser scientists and engineers to better understand the design recipe of selecting scanning filters and optimizing the nonlinear effects in the laser cavity and to learn how to produce sliding frequency pulses from erbium-doped fiber lasers. Such a wavelength-swept mode-locked laser is expected to be useful in applications in spectroscopy and biomedical imaging.
