Splitting a laser beam into two paths with a silvered mirror is a standard step in making a hologram.
The two resulting beams serve different purposes. One becomes the object beam, illuminating the subject and scattering light from its surface. The other becomes the reference beam, traveling directly toward a photosensitive recording medium. When the beams meet there, their coherent light produces a finely detailed interference pattern.
That recorded pattern—not the two beams by themselves—is the hologram. It stores information about both the intensity and phase of the light coming from the object. Later, shining an appropriate reference beam onto the developed recording reconstructs the object’s wavefront, creating the three-dimensional image associated with holography.
A common mix-up is thinking that a beam splitter instantly creates a floating projection. The mirror only divides the light; a subject, stable optical setup, recording material, and careful exposure are also required. Silvered mirrors and beam splitters are used because they can reflect part of the beam while transmitting the rest.