title: Coherent nature of the radiation emitted in delayed luminescence of leaves
abstract: After exposure to light, a living system emits a photon signal of characteristic shape. The signal has a small decay region and a long tail region. The flux of photons in the decay region changes by 2 to 3 orders of magnitude, but remains almost constant in the tail region. The decaying part is attributed to delayed luminescence and the constant part to ultra-weak luminescence. Biophoton emission is the common name given to both kinds of luminescence, and photons emitted are called biophotons. The decay character of the biophoton signal is not exponential, which is suggestive of a coherent signal. We sought to establish the coherent nature by measuring the conditional probability of zero photon detection in a small interval Delta. Our measurements establish the coherent nature of biophotons emitted by different leaves at various temperatures in the range 15-50 degrees C. Our set up could measure the conditional probability for Delta</=100 &mgr;s in only 100 ms, which enabled us to make its measurement in the decaying part of the signal. Various measurements were repeated 2000 times in contiguous intervals, which determined the dependence of the conditional probability on signal strength. The observed conditional probabilities at different signal strengths are in agreement with the predictions for coherent photons. The agreement is impressive at the discriminatory range, 0.1-5 counts per Delta, of signal strengths. The predictions for coherent and thermal photons differ substantially in this range. We used the values of Delta in the range, 10 &mgr;s-10 ms for obtaining a discriminatory signal strength in different regions of a decaying signal. These measurements establish the coherent nature of photons in all regions of a biophoton signal from 10 ms to 5 hr. We have checked the efficacy of out method by measuring the conditional probability of zero-photon detection in the radiation of a light emitting diode along with a leaf for Delta in the range 10 &mgr;s-100 &mgr;s. The conditional probability in the diode radiation was different from the prediction for coherent photons when the signal strength was less than 2.5 counts per Delta. Only the diode radiation exhibited photon bunching at signal strength around 0.05 count in Delta. Copyright 1999 Academic Press.
authors.affiliation: Institute of Self Organising Systems and Biophysics, North Eastern Hill University, Shillong, 793022, India.
authors.initials: RP
authors.lastname: Bajpai