Mon, Jan 14, 2013 @ 03:00 PM - 04:00 PM
Ming Hsieh Department of Electrical Engineering
Conferences, Lectures, & Seminars
Speaker: Claire Gmachl, Princeton University
Talk Title: “Mid-Infrared Quantum Cascade Lasers”
Abstract: Quantum Cascade (QC) lasers are a rapidly evolving mid-infrared and THz, 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 QC lasers, especially high efficiency and single-mode operation, and the implementation of unconventional laser schemes. We will also discuss several applications, such as field campaigns of QC laser-based sensing, and our recent work in non-invasive glucose sensing. 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. Next, we move on to unconventional designs, and a recent innovation in how the carrier injection into QC laser active regions is described; ultra-strong coupling between injectors and active regions are required, and the importance of interface roughness scattering is documented. The resultant QC lasers are nearly 50% power efficient at cryogenic temperatures. With respect to spectral innovations, a spectrally broadband QC laser based on a ‘continuum-to-continuum’ design will be presented, which differs from conventional, artificially spectrally broadened QC lasers in that almost no trade-off needs to be made between gain-bandwidth and laser performance with respect to laser threshold and output power. When this laser is put into an external cavity, a wide, continuous single-mode tuning range of well over 400 cm-1 is achieved. Next we explore opportunities for obtaining single-mode and tunable emission without the need of dispersive gratings, such as external dispersive cavities or gratings etched into the lasers. Folded cavities, “candy-cane“-shaped lasers, and Asymmetric Mach Zehnder cavities have all shown great potential for achieving single-mode emission at reduced fabrication complexity and cost. A recent example for the versatility of QC laser design is the development of QC lasers with two optical transitions in each active region instead of the usually just single photon emission. These lasers have potential for higher power efficiency and better performance especially at the long wavelength regime of l > 12 mm. Finally, we provide a quick overview on QC laser applications and show scattering of mid-infrared light from tissue components deeper in the skin potentially for non-invasive glucose sensing. The work presented is mostly supported by MIRTHE (NSF-ERC) with smaller contributions from other sources; the work has been conducted in collaboration with many valued colleagues in our own research group and across MIRTHE.
Biography: Claire Gmachl received the Ph.D. degree (sub auspicies praesidentis) in electrical engineering from the Technical University of Vienna, Austria, in 1995. In 1996, she joined Bell Laboratories, Lucent Technologies, Murray Hill, NJ, to work on Quantum Cascade lasers and microcavity devices. In 2003, Gmachl joined Princeton University as an Associate Professor in the Department of Electrical Engineering and adjunct faculty to PRISM; since July 2007 she is Full Professor at Princeton University, and a Eugene Higgins Professor of Electrical Engineering since 2011. Her group’s research is focused on mid-infrared photonics, especially Quantum Cascade lasers and applications. Gmachl is the Director of MIRTHE, the NSF Engineering Research Center on Mid-InfraRed Technologies for Health and the Environment, established in 2006. Gmachl has authored and co-authored more than 250 publications, has given more than 100 presentations at conferences and seminars, and holds 26 patents. She has won an E-council/GEC Excellence in Teaching Award in 2012, and a Princeton University graduate mentoring award in 2009; she was an Associate Editor for Optics Express and a member of the IEEE/LEOS Board of Governors. Gmachl is a 2005 MacArthur Fellow and a member of several professional societies.
Audiences: Everyone Is Invited
Posted By: Marilyn Poplawski