GaAs/AlAs Bragg mirrors on GaAs with varied number of pairs of layers, were grown by molecular beam epitaxy (MBE) to be applied for semiconductor saturable absorber mirrors (SESAMs) and intensity modulators. Due to the random variation of the growth rate, substrate surface roughness and interdiffusion at the interfaces it is diffucult to control perfectly the growth conditions of deposited layers. Thickness variations around the expected values and composition grading at the heterointefaces can be expected and consequently, variations of the mirror reflectivity. In this paper the X-ray diffraction, optical reflectance, Rutheford backscattering/channeling (RBS) supported by numerical methods were employed to determine both the exact thickness of each layer and the composition grading at the interface between succeeding layers of (Al)GaAs/AlAs-based mirrors. To speed up the process and to make the result more reliable, the diffraction curve, RBS and reflectivity spectra were simulated concurrently using results of one simulation to verify the others. This process was carried out until the best fit between experimental and calculated curves was achieved. It was shown that the X-ray diffraction method aided by numerical calculations is the most sensitive to the thickness variation of each layer and composition grading at the interfaces, but it was also shown that combining all the methods employed in this work significantly speed up the whole proces of resolving Braff mirror structure. And thanks to this sensitivity of X-ray diffraction it was possible to asses to what extend the thickness of each layer may be varied and composition grading at the interfaces modified so that only negligible modification of reflectivity spectrum would be observed.

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