TA09 15min10:57
ULTRASENSITIVE DUAL-BEAM ABSORPTION SPECTROSCOPY, BASED ON WAVELENGTH-MODULATION TECHNIQUE AND LOGARITHMIC NOISE CANCELING.

YU. KURITSYN AND V. LIGUER, Institute of Spectroscopy, Russian Academy of Science, 142092 Troitsk Moscow Region, Russia.

Various registration methods for ultrasensitive diode laser based absorption spectroscopy are discussed. The sensitivity of a single-beam wavelength modulation technique is limited by excess laser noises and wavelength-dependent effects in optical system. A dual-beam logarithmic detection allows to reduce excess laser noises but actually shot-noise level is not usually achieved and sensitivity is limited by low-frequency transmittance fluctuations and a flicker noise from atomizer. Simultaneous using a double-beam logarithmic detection and a wavelength-modulation technique allows to minimize a low-frequency noise contribution. Absorbance of 7×10-8/(Hz)-1/2 in such a system is demonstrated. Applications to trace measurements of chlorine in glow-discharge atomizer and lithium in graphite tube atomizer are described.