Even with incoherent light from the sun and not having any laser, Young achieves a result by reducing the incident light to a point-like source. This makes sense because a wider beam works like many pinholes. Each hole creates its own intensity distribution behind slits and there are no fringes visible. A further explanation of the pinhole highlights that the pinhole makes incoherent light coherent.
But how a pinhole makes light from a thermic source - for example from a sodium-vapor lamp - coherent?
Furthermore, does the light behind a hole then have the same properties as laser light?