The photoacoustic frequency spectrum under steady-state conditions from Philodendron green leaves attached to the plant was measured in the 0.2-200 Hz frequency range. The PA amplitude spectrum showed a maximum at low frequency (around 1 Hz) which was attributed to an optimum frequency for oxygen evolution. The signal decreased at a lower frequency, where the oxygen or carbondioxide uptake starts to become important. Efficiency of the oxygen evolution as a function of excitation light intensity was determined for different levels of background light.
Frandas, A., Jalink, H., & van der Schoor, R. (1997). Low frequency photoacoustics for monitoring the photobaric component in vivo of green leaves. Photosynthesis Research, 52(1), 65-67. https://doi.org/10.1023/A:1005805420477