PhD Proposal: Paul Burkins

TITLE: Femtosecond Z-scan measurements in novel materials with emphasis on managing thermal effects and mid-IR femtosecond spectroscopy of quantum cascade devices and lasers ABSTRACT: Military and civilian driven applications of nonlinear optics have been extended to include optical limiting materials to protect airline pilots and ground troop’s eyes from laser irradiation and for detectors to sense mid-infrared signatures of explosives. Optical limiting incorporates nonlinear optical materials which can be characterized by the Z-scan technique. This technique is calibrated with materials with known nonlinear refraction and nonlinear absorption profiles, such as CS₂ and ZnSe. Part of this proposal is to attempt to eliminate or reduce thermal effects, which can dominate due to their large yet typically slow nonlinear response, and to develop a sample calibration methodology consistent enough to move on to new and unknown samples of interest. In addition to optical limiting, we also have an interest in studying highly nonlinear materials for all optical ultrafast switching, such as chalcogenide films and graphene in solution.
Mid-IR detection using HgCdTe (MCT) or InSb typically requires cryogenic temperatures for operation. Quantum cascade detectors (QCDs) can operate a room temperature and utilizes long wavelength intersubband (ISB) transitions for mid-IR detection. Carrier lifetimes are estimated to be on the order of 1-ps in QCDs. A tunable fs mid-IR source will be utilized for pump-probe spectroscopy of carrier dynamics and carrier lifetime measurements in QCDs. Room temperature ultrafast mid-IR detectors are nearly non-existent – the proposed research on QCDs may be the solution to this problem.