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Mid-Infrared Quantum Cascade Lasers

Type: Colloquium
Date/Time: 2009-05-11 16:00
Location: Weniger 153
Event speaker: Prof. Claire Gmachl, Princeton
Title: Mid-Infrared Quantum Cascade Lasers
Contact: Podolskiy

Abstract

Quantum Cascade (QC) lasers are a rapidly evolving mid-infrared, semiconductor laser technology based on intersubband transitions in multiple coupled quantum wells. The lasers’ strengths are their wavelength tailorability, high performance and fascinating design potential.

We will first give a brief introduction into QC lasers followed by a discussion of several recent highlights, such as the quest for high performance, especially high efficiency operation and the implementation of unconventional laser schemes, and applications, in particular our field campaign to participate in air quality measurements during the 2008 Beijing Olympics.  

As an example for high-performance QC lasers, we examine lasers around 5 mm wavelength.  First, we focus on thorough engineering of conventional QC lasers.  The quest for high power and high efficiency QC lasers requires these lasers to have a low intrinsic threshold, a high characteristic temperature, a low voltage defect, and superior heat sinking.  QC lasers with several percent wall-plug efficiency at room temperature and few 10% efficiency at low temperatures are possible.  Next, we move on to unconventional designs, and a recent change (shall we call it a “paradigm shift”?) in how the carrier injection into QC laser active regions is described.  The resultant QC lasers are nearly 50% power efficient at cryogenic temperatures.

In summer 2008 our group deployed two QC-laser based trace gas sensors for air-quality measurements in Beijing, China, hosted by the Institute of Atmospheric Physics of the Chinese Academy of Science.  The Beijing Olympics provided us with an ideal test-bed to participate in an important event and contribute engineering solutions, to observe the substantial civil engineering project of cleaning a mega-city’s air in only a few weeks, and to stress-test the up-start technology of QC-laser based sensors.  An open path (75 m) mid-infrared absorption spectrometer containing a widely tunable QC laser was used to study H2O, NH3, O3, and CO2 levels before, during, and after the Olympic Games in an effort to capture changes induced by emissions reduction methods.  Time permitting, we will cover some topics of mid-infrared material science, such as optical metamaterials including those presenting negative refraction.

This work is mostly supported by MIRTHE (NSF-ERC) with smaller contributions from other sources; the work presented is a collaboration with many valued colleagues in our own research group and across MIRTHE.

Refreshments will be served half an hour before the start of the colloquium in Weniger 305.