Development of an Ultrasensitive Ultrafast Phase Spectrometer

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

A grant has been awarded to Drs Trebino and El-Sayed at the Georgia Institute of Technol-ogy to develop a novel ultrasensitive ultrafast intensity-and-phase spectrometer, which yields the full intensity and phase vs. time (or frequency) of luminescence and other light pulses relevant to biology and many other fields. The spectrometer will have a very high sensitivity for single-shot measurements and a <1-photon-per-pulse sensitivity for multi-shot measurements. These sensitivi-ties are approximately six orders magnitude better than those of current measurement techniques. The proposed instrument involves combining a spectrometer with a coherent reference light pulse. Specifically, it will use an ultra-short pulse with a spectrum ranging from 400 nm to 1600 nm and generated by propagating readily available, low-energy, 100-fs pulses through microstruc-ture optical fiber (recently developed by Lucent Technologies. Demonstrations of the new instru-ment will involve simple photochemical systems relevant to photobiology. Examples include dou-ble proton transfer processes in 7-azaindole and its analogues (important in understanding radiation-induced DNA mutation) and the photo-isomeri-zation around double bonds, e.g., in the merocyanine dyes (important for understanding of the primary processes in proteins of vision, such as rhodopsin and bacteriorhodopsin photosynthesis). Later, we propose to use this device to further understand the complex primary dynamics in bacteriorhodopsin and to distinguish between different theoretical models proposed for its primary photo-dynamics. This instrument will also have applications far beyond biology. For example, semi-conductor experiments often generate weak light pulses of new wavelengths, which cannot be measured with conventional methods, but potentially can with this. Also, astronomers routinely measure the intensity vs. frequency (the spectrum) of light from astrophysical sources, but they cannot currently measure the spectral phase. With this instrument it should be possible to do so and yield information previously unavailable regarding extraterrestrial light sources. In addition, the spectrometer will allow measurements of the phase of signal and idler beams in a broadband optical parametric generators-a system that is interesting because the phase of these two beams is quan-tum-mechanically entangled with many degrees of freedom and so can be used for quantum com-puting. Finally, the ultrafast intensity and phase vs. time of virtually any light-emitting medium could be studied using this highly sensitive instrument.