# Fourier mode expansion of the scalar field in Rindler space - Unruh effect

I am reading 't Hooft's notes on Black Holes. In the section on Unruh effect, he says:

Please see this question for what is $K$ and $\mu$.

I am not being able to make any sense of equation? What is the $\ln(\frac{k_3+k_0}{\mu})$ for? Why are we not doing the same Fourier sum, as that during the canonical quantization of a scalar field?

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It is a quantization of a scalar field but not quantization on the flat space. So there are more complicated solutions than just the plane waves and the coefficients of these generalized plane waves may have more subtle commutators etc. He uses several sets of the creation/annihilation operators that minimize different kinds of energy, and so on. –  Luboš Motl Jul 14 '13 at 6:55