Acquisition of an Optical Parametric Amplifier (OPA) Laser System

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

0076429 Merlin, Roberto D An award is made to the University of Michigan for the acquisition of an Optical parametric Amplifier (OPA). The OPA will be used to generate a tunable ultrashort optical pulses to probe, and control coherent phonons in solids using resonant excitation and to study the interaction of photogenerated carriers with phonons. In particular, quantum dot systems, to investigate "phonon bottleneck". The bottleneck is important for unipolar intersubband devices such as mid-infrared detectors, since a long excited state lifetime enables reduced noise, but detrimental to bipolar interband devices such as near-infrared lasers, as it limits the modulation bandwidth. The interaction of hot carriers with impulsively generated coherent phonons is an additional new area of exploration. The hot carriers should give rise to stimulated phonon emission which may be useful for controlled ultrafast tunneling in phonon-assisted-tunneling devices, and for the development of "phonon lasers." The OPA system will also be used for photon echo and fluorescence up-conversion measurements in chemical and biological systems, particularly reaction centers of photosystem II. Fluorescence up-conversion will be used to probe the excited state population in the reaction centers directly and test models for the charge separation process. Photon echo experiments will provide important information on the coupling between the pigment electronic states and the solvent (protein) bath. The instrument will be used in the training of graduate and undergraduate students who will be the primary users. Several groups at the University of Michigan will be able to use the instrument for their NSF funded research. *** This is an instrument acquisition award to the University of Michigan. The principal investigators will purchase an Optical parametric Amplifier (OPA). When light shines on a semiconductor material, electrons which are tightly bound to the atoms in the material are "freed up" to move throughout the semiconductor. When the initial energy of the electrons is high, they are referred to as "hot" electrons. If the exciting light is in the form of a short (femtosecond) laser pulse, then the pulse generates a burst of hot electrons. These electrons will not stay hot, but will rapidly cool down to the crystal temperature by generating crystal vibrations, or "phonons." The cooling process can be controlled in sophisticated ways. For example, if the semiconductor contains quantum dots, in which the electronic states are discrete, then the cooling rate can be vastly reduced. The study of the reduced cooling rate (referred to as the "phonon bottleneck") will be useful for the development of new infrared detectors and lasers. The study of this process may lead to new semiconductor device concepts. Light shining on photosynthetic proteins in green plants also results in electron motion, this time in a protein and across a membrane with the potential used to produce oxygen and carbohydrates. This new instrument will be used in this type of research and other NSF funded research at the University of Wisconsin. Graduate and undergraduate students will benefit tremendously by using this instrument and techniques in well designed research projects.