FIBEROPTIC PROBES WITH IMPROVED EXCITATION AND COLLECTION EFFICIENCY FOR DEEP-UV RAMAN AND RESONANCE RAMAN-SPECTROSCOPY

The ability of ultraviolet resonance Raman spectroscopy (UVRRS) to det ermine structural, environmental, and analytical information concernin g low-concentration aqueous biomolecules makes it a powerful bioanalyt ical and biophysical technique. Unfortunately, its utility has been li mited by experimental requirements that preclude in situ or in vice st udies in most cases. We have developed the first high-performance fibe r-optic probes suitable for long-term use in pulsed UVRRS applications in the deep-UV (DUV, 205-250 nm). The probes incorporate recently dev eloped improved ultraviolet (IUV) fibers that do not exhibit the rapid solarization and throughput decay that previously hampered the use of optical fibers for delivering pulsed, DUV light. A novel 90 degrees m irrored collection geometry is used to overcome the inner-filtering ef fects that plague Bush-probe geometries, The IUV fibers are characteri zed with respect to their efficacy at transmitting pulsed, DUV laser l ight, and prototype probes are used to obtain pulsed UVRRS data of aro matic amino acids, proteins, and hormones at low concentrations with 2 05-240-nm pulsed excitation. Efficient probe geometries and fabricatio n methods are presented. The performance of the probes In examining re sonance-enhanced Raman signals from absorbing chromophores is investig ated, and the optimal excitation wavelength is shown to be significant ly red-shifted from the maximum of the resonance Raman enhancement pro file. Generally applicable procedures for determining optimal experime ntal conditions are also introduced. (C) 1998 Optical Society of Ameri ca.