emitted by a diode pumped solid state laser of wavelength u03bb 532 nm is first of all linearly polarized by a polaroid filter and then circularly polarized using a u03bb 4 plate with u03bb 532 nm the laser beam thus polarized is then passed through the oriented acrylate composition since acrylate compositions are highly transparent the laser beam is able to pass through the composition virtually unhindered where the polymer molecules of the acrylate composition are oriented this results in a change in the polarizability of the acrylate composition depending on observation angle birefringence as a result of this effect the e vector of the circularly polarized laser beam undergoes a rotation about the axis of progression of the laser beam after departing the sample the laser beam thus manipulated is passed through a second u03bb 4 plate with u03bb 532 nm whose optical axis deviates by 900 from the optical axis of the first u03bb 4 plate this filter is followed by a second polaroid filter which likewise deviates by 90 u00b0 from the first polaroid filter finally the intensity of the laser beam is measured using a photosensor and u03b4n is determined as described under version 1 after careful drying the solvent free adhesive samples are welded into a pouch made of polyethylene nonwoven tyvek nonwoven the gel index is determined from the difference in the sample weights before and after extraction with toluene strips of the specimens with a width of at least 30 mm and a length of 50 mm were laminated to form a sample element and to give a thickness.