Derivative Photoacoustic Spectroscopy And Its Application

This thesis presents a new method that applies time resolution technology into the realization of derivative spectroscopy. By the new method, we construct a system for experiment that consists of a monochromator, a prism divider and a modulator. The prism divides the light beam that comes out of the monochromator into two beams of identical intensity and equal wavelength, which are vertically parallel. And the two beams are lead through the modulator systematically with the upper beam running at a supposed t time when its wavelength is A and the lower one at a supposed t + At time when its wavelength A + AA due to the constant scanning from the monochromator. The modulator modulates the two beams, phase between the two beams being π. And when two beams are brought to one point, intensities of the two beams differentiate each other. Then we obtain the first-order derivative spectroscopy by scanning wavelength of the monochromator. The experiment with He-Ne laser and Xe lamp as its light source indicates that the system is able to get the first-order derivative spectroscopy which is better than the original spectroscopy in terms of resolution.The principle of derivative photoacoustic spectroscopy prescribes that the acquisition of derivative photoacoustic spectroscopy demands the two conditions be met. One is that two beams of identical intensity but of minor differences in wavelength are brought into the photoacoustic detector to produce S(λ + △λ) and S(λ) , the photoacoustic signals, respectively in the meantime. The other is the differentiation between S(λ + △λ) and S(λ). There are two ways for us to obtain the first-order derivative photoacoustic spectroscopy.The first method involves the application of thewavelength-intensity divider, which consists of a monochromator and prism. The prism divides the beam out of the monochromator into two eudipleural beams of identical intensity but of minor differences in wavelength. The two beams modulated by the modulator are brought together, the differentiation between two photoacoutic signals produced by the two beams being realized. With the two conditions being met, scan the monochromator to obtain derivative photoacoustic spectroscopy.The second involves the application of the time resolution technology. We combine the time resolution technology as well as photoacoustic spectroscopy technology into the designing of an experimental system which takes He-Ne laser as its light source and carbon as its sample. Experiments indicate that the system is able to realize the first-order derivative photoacoustic spectroscopy successfully. The result shows that the derivative photoacoustic spectroscopy has both the advantages of enjoying photoacoustic spectroscopy with high sensitivity and universality as well as derivative spectroscopy with high resolution.