to show how the holographic windows of fig3 a and 3c may be used in hand held portable laser bar code scanners it will be appreciated of course that windows of the type shown in fig3 could also be used in other scanners such as fixed installations fig4 a and 4b illustrate a conventional bar code scanner using a conventional transmissive scan window 13 as may be seen in fig4 b the scanner produces a scanning beam having a beam waist 26 the beam scans across a scan angle 24 providing symbol reading capabilities throughout a working range 22 in front of the working range there is a dead zone 20 within which a bar code symbol is normally too close to the scanner housing to be properly decoded as may be seen in fig4 c the replacement of the conventional window 13 with a suitable holographic window 113 may eliminate the dead zone and may improve the working range to a new value 122 the scan angle 24 may also be improved and widened to a new scan angle 124 this may be achieved by making use of a hologram which has a spatial frequency distribution given by equation 2 in which the focal length f is negative this produces a holographic window which is in many ways equivalent to a negative lens a wide angle scanner of this type is efficient for high density bar code reading fig5 a and 5b show a second application of a holographic window fig5 a.