The current experimental investigation focuses on two-dimensional unsteady laminar boundary layers and their response to different extents of adverse pressure gradient. It finds numerous applications ranging from pulsating flow in arteries, flow over flapping wings of birds and fins of fish to some technologically important ones as in flow over the blade surface of compressor and turbines in gas turbine engines. Short, long and infinitely long two-dimensional laminar separation bubbles, generated over two tangent hyperbolic geometries that resemble rounded backward facing step, and a flat plate respectively, are investigated experimentally in a special type of unsteady water tunnel. In all the experiments the freestream velocity in the channel has a trapezoidal variation with time. The infinitely long bubble evolves from adverse temporal component. Vortex formation time and wavelength of vortices scale with the average convective time scale and mean boundary layer thickness respectively, the average being taken from the start of reverse flow to appearance of a vortex. Short and long bubbles are initiated by the combined effect of adverse pressure gradient and skin friction. Scalings are obtained for initiation and growth of the bubble in the constant velocity phase. Vortex formation time varies inversely with Re. Spatio-temporal evolution of vorticity, velocity, skin friction coefficient along the geometry and time variation of its spatial average were studied in detail. Strong spatial component keeps the short bubble intact for considerable time while the long one begins to deform early with subsequent onset of shear layer instability. In case of long bubble, vortex shedding is observed in the deceleration phase above a critical Re. Characteristics of unsteady separation like ejection of fluid particles along the line of zero vorticity and appearance of saddle point are clearly seen in the experiments. Evolution of long bubble during deceleration resembles that over rapidly pitching airfoils.