The semiconductor laser diode as an excitation source for analytical atomic and molecular fluorescence spectroscopy.

摘要

The feasibility of laser diode (LD) excitation for analytical fluorescence techniques was investigated in this work. The spectral characteristics of single-mode and high-power array laser diodes were examined with a monochromator, a diode array detector, and a fourier transform Michelson interferometer. The tuning of LD wavelength with temperature and electrical current was also studied.;Experiments in frequency doubling of the laser diode were carried out and compared to results predicted by theory. Temperature tuning of the frequency-doubled LD was demonstrated. The frequency-doubled LD was tuned to 403 nm to excite gallium atoms in a graphite furnace, but it proved to have insufficient intensity to produce a detectable amount of gallium atomic fluorescence. The doubled LD was used more successfully to excite molecular fluorescence. Perylene, a polyaromatic hydrocarbon, was detected in hexane at a level of 100 ppb.;Both high-power and single-mode LDs were used to excite rubidium atomic fluorescence. Limits of detection were 2.1 pg in a graphite furnace and 200 ng in a glow discharge. Amplitude and frequency modulation were used to discriminate against emission background.;Molecular fluorescence of the organic dye IR-140 was excited with both types of LDs, in four different instrumental configurations. The first and simplest approach was a compact, inexpensive filter fluorometer which could be made portable. Luminescence was measured with a red sensitive photodiode. In the second configuration, the laser beam was collimated and passed through the cuvette; luminescence was measured with a monochromator and cooled photomultiplier tube. A concentrational detection limit of 10