Joint IEEE ACT Photonics/EDS Chapter and the group of Electronic Materials Engineering (ANU)

Title: Thermodynamically-Limited Uncooled Infrared Detection Using Meta-Optics and Particle-Induced Laser Damage on Optical Materials

Date & Time: Friday 1st of March, 11:00 am (AEDT)

Location: Australian National University, Research School of Physics, Bldg #60, Seminar Room 4.03 (New Bldg)

Speaker: Professor Joseph (Joey) Talghader

Electrical and Computer Engineering, University of Minnesota

[email protected]

Abstract: One of the historical goals of infrared detection has been to reach the background limit, where the noise of measurement is limited by photon fluctuations from the observed object, with a room temperature device. Recent work in my group with optomechanical thermal detectors has reached within a factor of 3.6 of that limit, the closest ever achieved, such that the thermodynamic processes of photon and phonon fluctuations contribute 98% of the measurement noise. The concept behind this was that one can use meta-optics can be used to create structures with extraordinarily high absorption per unit mass. The detector is a metal-dielectric-metal structure patterned on a subwavelength scale such that it is mostly open space. This creates an effective medium that couples highly to free space and even the gaps between pixels contribute to the absorption. The detector performed with a detectivity of 3.8 x 10⁹ cmHz^1/2/W and NETD of 4.5mK in the long-wave infrared (λ ~ 8-12μm) with a time constant of 7.4ms.

Particles are ubiquitous in all but the cleanest laboratory environments. Whether these particles are suspended in air or deposited on surfaces, they create a radically different environment than what is typically considered during optical testing. However, dirt does not make (laser-induced) optical breakdown a random process. Our recent studies have shown that one can predict with high accuracy which contaminated optical materials will fail early and in which order it will happen. A high power laser illuminating an absorbing particle heats it to thousands of degrees Kelvin, and the particle begins evaporating. The heat transfers to the underlying substrate, and if it reaches a certain value, then the optical substrate or coating will start to thermally generate electron-hole pairs. These carriers will absorb further light and at a certain concentration, the entire optic will fail, occasionally drilling a hole through the entire thickness of the substrate. This process has a very strong bandgap dependence. Similar behavior has been observed for metal particles in air where lasers can accelerate particles to high velocity into their own optics causing catastrophic failure. In this talk, we will discuss the physics of optical breakdown in the presence of dirt and the practical consequences it has on optical system design.

Biography:

Joseph Talghader obtained his B.S. in electrical engineering from Rice University. He was awarded an NSF Graduate Fellowship and attended the University of California at Berkeley where he received his M.S. and Ph.D, also in electrical engineering. After working in industry at Texas Instruments and WSI,  Dr. Talghader joined the faculty at the University of Minnesota where he is now a Professor. His research group works in the areas of directed energy and micro-and nano-optical systems. Among his honors Professor Talghader is a Fellow of Optica (Optical Society of America), has received the Antarctica Service Medal of the United States, and, during his sabbatical year, he is a Fulbright and Visiting Fellow at the University of Western Australia and the TI Visiting Professor at Rice University.