A Theoretical and Experimental Investigation of the Thechnique of Laser Intermodulated Fluorescence for Scattering Correction in Atomic Fluorescence Flame Spectrometry

A THEORETICAL DERIVATION IS PRESENTED OF THE SIGNAL OB- TAINED WITH THE TECHNIQUE OF INTERMODULATED ATOMIC FLUO- RESCENCE SPECTROSCOPY. ONE LASER BEAM, TUNED AT A SELEC- TED ATOMIC TRANSITION, IS DIVIDED INTO TWO BEAMS WHICH ARE THEN AMPLITUDE MODULATED AT DIFFERENT FREQUENCIES AND RECOM- BINED IN A FLAME CONTAINING THE VAPOUR OF THE ELEMENT INVESTI- GATED. THE FLUORESCENCE SIGNAL AT THE SUM OR DIFFERENCE FRE- QUENCY IS MEASURED. THE DERIVATION IS GIVEN FOR BOTH SQUARE WAVE AND SINUSOIDAL MODULATION. IT IS SHOWN THAT THE INTER- FERENCED FLUORESCENCE AMPLITUDE DEPENDS UPON THE SQUARE OF THE LASER SPECTRAL IRRADIANCE AT LOW POWERS AND REACHES A PLATEAU AT HIGH IRRADIANCE BUT ONLY IN THE CASE OF SQUARE WAVE MODULATION. FOR SINUSOIDAL MODULATION, A MAXIMUM IS REACHED FOLLOWED BY A ROLL-OFF AT HIGH IRRADIANCE. THE THEO- RETICAL PREDICTIONS ARE VERIFIED EXPERIMENTALLY WITH A SQUA- RE WAVE MODULATED CW DYE LASER FOR THE CASE OF SODIUM RESONAN- CE FLUORESCENCE IN AN OXYGEN-ARGON-HYDROGEN FLAME. THE SCAT- TER SIGNAL HAS NO INTERMODULATION COMPONENT. FINALLY, IT IS SHOWN THAT WHEN THE MODULATION WAVEFORM IS NOT SQUARE WAVE, SCATTERING CORRECTION CAN ALSO BE ACHIEVED WITH A SIMPLE BEAM EXCITATION SCHEME.

ALKEMADE C.Th.J.; 

1995-03-15

JRC4003

https://publications.jrc.ec.europa.eu/repository/handle/JRC4003,