Thermodynamics of electromagnetic radiation?

[Andy Resnick]

Does anyone know a good reference which discusses the thermodynamics of electromagnetic radiation? Not blackbody radiation, or radiative transfer, but assigning thermodynamic quantities (temperature, entropy, free energy, etc.) to the field itself?

The initial question is simple enough: What's the temperature of a laser beam?

The only decent references I could find are:

Madel & Wolf, "Optical Coherence and Quantum Optics" , chapter 13
Essex, Kennedy and Berry,"How Hot is Radiation?", Am. J. Phys 71, 969-978 (2003)

Essex's derivation requires a quantum description of the field- and since photon number is not conserved, it's not clear how applicable their result is. Mandel and Wolf discuss "thermal light", but I couldn't make heads or tails of their results.

I'm thinking about simple things: even blackbody radiation that has passed through a (passive) spectral filter- what's the thermodynamics?

Any help is appreciated.

 

[Greg Bernhardt]

@Andy Resnick did you gain more insight on this?

 

[Andy Resnick]

@Andy Resnick did you gain more insight on this?

Unfortunately, no. I got as far as "Only blackbody radiation can be ascribed a temperature." and no further. I figured someone considered the thermodynamics of radiation with a spectrum that is slightly different than a blackbody spectrum: is that a nonequilibrium system and if so, how could it relax to equilibrium? Can work be extracted from nonequilibrium radiation fields? But I couldn't find anything published.

Maybe someone else has an idea or three...