# Cartan decomposition of measure of $GL(2, \mathbb{C})$

I am searching for a integration formula

$$\int\limits_{GL_2(\mathbb{C})} \phi(g) d g = \int\limits_{SU(2)} \int\limits_{SU(2)} \int\limits_{M} \phi(k_1mk_2) \omega(m) d m d k_1 d k_2 ,$$ where $M$ is the subgroup of diagonal matrices. I am in particular interested in an explicit form for the weight $\omega$ preferably with reference.

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I found now a reference for $\mathrm{SL}(2,\mathbb{C})$ in Brummelhuis, Koornwinder "The generalized Abel transform" Lemma 5.5.
Answer: $\omega$ is trivial on the center and on a diagonal matrix with entries $e^t$ and $e^{-t}$ a scalar multiple of $|sinh(2t)|^2$. The scalar depends of course on the chosen Haar measure.
This is also in Jorgenson-Lang, "The heat kernel and theta inversion on $SL_2(\mathbb C)$". If you want things to have a central character, $SL_2(\mathbb C)$ is sufficient. –  B R May 21 '12 at 17:31