Deep Ultraviolet Laser Diode for UV-Resonance Enhanced Raman Identification of Biological Agents

This proposal addresses the need for deep UV semiconductor lasers for use in UV resonance enhanced Raman spectroscopic identification of biological agents. The proposed approach avoids the problems of p-doping and ohmic contacts by using subminiature direct electron injection excitation of an InAlGaN heterostructure. We have demonstrated strong stimulated emission at 274nm using this approach with measured linewidth reduction from 16nm to 4nm and five orders of magnitude non-linear increase in intensity. High levels of chemical specificity can be obtained using Raman spectroscopy without sample preparation, contact, or destruction. When Raman excitation occurs within the electronic resonance band of a material the scatter cross-sections can improve as much as eight orders of magnitude. For biochemical molecules such as nucleic and amino acids these absorption bands are very strong in the deep UV between about 220nm and 280nm. When Raman excitation is below about 250nm, there is a fluorescence-free region extending over 4000 wave numbers above the excitation wavelength providing very high detection sensitivities and low background noise. It is the goal of this proposed program to demonstrate deep UV emission from a semiconductor laser and the ability to obtain deep UV resonance Raman spectra of analogs of hazardous biological agents.