LIFETIME FLUORESCENT MICROSCOPE

ANALYTICAL TECHNIQUES BASED ON FLUORESCENT LIFETIME MEASUREMENTS ARE CURRENTLY BEING DEVELOPED FOR APPLICATIONS IN CLINICAL CHEMISTRY AND BIOLOGICAL RESEARCH. BY MEASURING THE PHASE OF THE FLUORESCENT EMISSION FROM A SAMPLE RELATIVE TO THAT OF AN RF-MODULATED EXCITATION SOURCE, IT IS POSSIBLE TO DETERMINE THE FLUORESCENT DECAY RATE ACCURATELY. ALTHOUGH SENSITIVE PHASE FLUOROMETERS HAVE BEEN CONSTRUCTED IN A NUMBER OF RESEARCH LABORATORIES, THEY REQUIRE THE USE OF LARGE, EXPENSIVE LASER SOURCES TO EXCITE THE FLUORESCENT SAMPLE. THE COMMERCIAL INTRODUCTION OF A PHASE FLUOROMETER REQUIRES THE DEVELOPMENT OF COMPACT, EFFICIENT LASER SOURCES WITH THE CORRECT COMBINATION OF OUTPUT POWER, WAVELENGTH, AND MODULATION BANDWIDTH. DIODE-PUMPED INTRACAVITY SUM FREQUENCY LASERS CAN BE MODULATED AT RATES UP TO 1 GHZ AND ARE CAPABLE OF PRODUCING OUTPUT POWERS IN THE BLUE AND GREEN THAT ARE GREATER THAN 25 MW. RESEARCHERS ARE INVESTIGATING THE FEASIBILITY OF USING A SUM FREQUENCY LASER TO EXCITE THE SAMPLE IN A PHASE FLUOROMETER. A 490 NM SUM FREQUENCY LASER IS BEING BUILT AND ITS MODULATION BANDWIDTH AND OUTPUT POWER DETERMINED. THE SOURCE IS THEN IMAGED INTO A COMMERCIAL FLUORESCENCE MICROSCOPE AND THE MODULATION DEPTH OF THE FLUORESCENT OUTPUT DETERMINED AS A FUNCTION OF INPUT FREQUENCY.