A simple technique is presented to obtain normalized photoacoustic (PA) spectra corrected for the spectral variation of the source in a single scan. The input light beam is passed through the center of a dual slot chopper, which splits it into two chopped output beams at two different frequencies at a fixed ratio. The beams fall on the sample and the reference kept side-by-side in the same sample chamber. The PA signals are detected by a microphone and processed by two lock-in amplifiers tuned at two different frequencies. The technique is tested by recording the PA spectra of standard samples.

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