Photoacoustic effect as a liquid absorbance detector

A theoretical treatment of the photoacoustic effect for a liquid enclosed in a cylindrical cell is given. Simple analytical expressions for the photoacoustic signal are derived for cw and pulse modulation schemes. Modulation frequency or pulse width dependence of the photoacoustic signal is discussed. For the cw modulation scheme it is found that more photoacoustic power is generated in a resonant cell than a nonresonant cell at the expense of bandwidth reduction. Conditions leading to 1/f dependence of the signal on modulation frequency are given. Experimental results are presented that support the simplified treatments. Eventual sensitivities of various excitation schemes under optimum conditions are calculated.