Alignment and Transient Noise Reduction in aLIGO

After a very successful third observation run, the aLIGO detectors are undergoing upgrades in preparation for the fourth observation run. Alignment noise is one of the largest contributors of noise at low frequency in the detection bandwidth. The mirrors of the detector are actively aligned to maintain resonance in the optical cavities. In this talk I will discuss the ongoing effort to reduce this alignment noise. I will also present about transient noise and its possible links to the alignment control loops.