Abstract Laser voltage probing (LVP) has been extensively used for fault isolation over the last decade; however fault isolation in practice primarily relies on good-to-bad comparisons. In the case of complex logic failures at advanced technology nodes, understanding the components of the measured data can improve accuracy and speed of fault isolation. This work demonstrates the use of second harmonic and thermal effects of LVP to improve fault isolation with specific examples. In the first case, second harmonic frequency is used to identify duty cycle degradation. Monitoring the relative amplitude of the second harmonic helps identify minute deviations in the duty cycle with a scan over a region, as opposed to collecting multiple high resolution waveforms at each node. This can be used to identify timing degradation such as signal slope variation as well. In the second example, identifying abnormal data at the failing device as temperature dependent effect helps refine the fault isolation further.