Joint MtSE-Physics Dept Seminar

September 30, Friday (** SPECIAL DAY**)

Ultrafast Optical Characterization of Novel Mid-Infrared Nanoscale Structures

Dr. Anthony M. Johnson

Director, Center for Advanced Studies in Photonics Research

Professor of Physics, Computer Science & Electrical Engineering

University of Maryland, Baltimore County

(Optics & Materials Physics, Host: Ravindra)

Time: 11:45am-12:45pm with 11:30am tea time

Room: ECE 202

Ultrafast optical phenomena refers to dynamical processes that occur in various forms of matter on the timescale of picoseconds (10^-12 s, ps), femtoseconds (10^-15 s, fs) and attoseconds (10^-18 s, as). These phenomena are relegated to the optical domain, primarily because only lasers have been fast enough to probe many of these processes. Ultrashort pulses of light have been utilized in fundamental studies of disciplines as diverse as semiconductor physics, lightwave transmission systems and biological systems. Mid-Infrared (Mid-IR) optical spectroscopy rests on the fact that practically all chemicals are uniquely identifiable by their vibrational spectra through optical probing of absorption or transmission and that the strongest vibrational resonance frequencies are in the mid-IR (λ ~ 3-30 µm). Mid-IR lasers are thus needed to perform this spectroscopy and one such laser is the quantum cascade laser (QCL). There are fundamental processes in the QCL that occur on fs and ps timescales and thus the need for an ultrafast mid-IR laser. In this talk, I will discuss the generation and use of fs mid-IR optical pulses to investigate the ultrafast gain dynamics and nonlinear optical properties of active mid-IR semiconductor QCLs. These mid-infrared QCLs are fundamentally different from the traditional visible and near-infrared semiconductor lasers that are common in everyday DVD players and supermarket scanners – these differences will also be discussed.

This work was partially supported by NSF MRI Grant NSF ECS-0619548 and MIRTHE Grant NSF ERC-0540832.

A. M. Johnson, Bio: http://physics.umbc.edu/people/faculty/johnson/