The response of a low-speed turbulent mixing layer to perturbations from a pulsed Nd:YAG laser and an ns-DBD plasma actuator is examined experimentally. The objective of this work is to further clarify the mechanisms associated with flow control via thermal perturbations (energy deposition). The results are placed in context by contrasting them with previous work on the same facility using ac-DBD plasma actuators which function through electrohydrodynamic effects (i.e. momentum). The mixing layer is examined downstream in a region of maximum possible growth using total pressure measurements, PIV and hot wire anemometry where possible. The observed velocity fluctuations are compared between different actuation techniques. Attention is then shifted to the mixing layer origin (splitter plate trailing edge) to provide an understanding of the nature of the perturbations that result in downstream mixing layer growth. PIV and schlieren in this region show that the laser generates a discrete perturbation that propagates downstream resembling an impulse response. Single pulse ns-DBD forcing is absent any clear effect, but burst mode forcing produces fluctuations that suggest thermal excitation rather than momentum-based perturbations as observed in ac-DBDs. In the context of previous work, these results suggest that ns-DBDs (and thermal perturbations in general) are capable of increased control authority using a higher energy single pulses (e.g. Nd:YAG laser) or high frequency bursts (e.g. ns-DBD). These results also provide implications regarding the spatial distribution of heating, convective behavior of the heated gas and amplitude scaling of thermal perturbations for flow control.