ELFT HÍRADÓ

[Szeminárium koordinátor <sem-admin AT szfki.hu>]

SZFI SeminarVarró SándorWigner FK SZFI, ELI-ALPSNotes on black-body radiation 
and stimulated emissionTuesday, 15 December 2020, 10:00, video conference, 
https://letsmeet.wigner.hu/szeminariumThe study of the physical bases of 
stimulated emission and black-body radiation have been closely related from 
the very beginning. We feel it justified to devote some time for their joint 
analysis, in particular, in the present year, when we celebrate the 60th 
anniversary of the invention of the LASER (Light Amplification by Stimulated 
Emission of Radiation). Moreover, one should also keep in mind that in the 
course of his work on black-body radiation, Planck discovered the elementary 
quantum of action h just 120 years ago. In the present talk, though we shall 
highlight some moments in the development of the laser during the past 60 
years, the emphasis shall be put on the fundamental aspects. Our purpose is 
on one hand to discuss some lesser known historical facts concerning the 
stimulated emission of radiation as appeared in the works of Planck (1911) 
and Einstein (1916). On the other hand, we present our recent results; a new 
phenomenological derivation of the entropy of a Planckian oscillator, and the 
building up of its connection with the fractal dimension of the relative 
frequencies of the excitation of a Bohr atom in thermal equilibrium. In the 
first part of the talk, we summarize Einstein’s famous derivation (1916) of 
the Planck formula for black-body radiation, in which he introduced the 
concept of stimulated emission. Then we discuss Planck’s so-called second 
theory (which have been worked out earlier, in 1911) and show that it already 
implicitely contained the process of stimulated emission (besides the 
zero-point energy and the so-called Bose distribution). On the basis of 
critiques by Landé (1925) and Heitler (1925) of Einstein’s derivation we draw 
attention to the correct interpretation of the so-called ‘A and B 
coefficients’. In the second part of the talk, we show that if we map the 
relative frequencies of the excitations of a two-level system to the unit 
interval, then the Planck entropy is directly connected to the 
(temperature-dependent) Hausdorff dimension of the set of excitations 
represented in this interval. Finally, we shall go back to the very 
beginnings, and consider Planck’s interpolation formula for the entropy, 
which resulted in the first correct expression for the spectral density of 
the black-body radiation 120 years ago. We will show that by relaxing the 
phenomenological scaling law for the ‘degree of irreversibility’ introduced 
by Planck, it is possible to derive this entropy formula, without any 
apparent quantization.   Minden érdeklődőt szívesen látunk! - Everyone 
is welcome to attend.Róbert Juhászsem-admin AT szfki.hu