is positioned within the openings 54 this design eliminates the need for the reflectors 58 on the inner surfaces 56 of the showerhead 26 seals 71 are provided between the windows 68 and the showerhead 26 and between the housing 62 and the showerhead 26 alternatively as shown in fig4 the window 68 may be located on the lower surface 48 of the showerhead 26 in that embodiment holes 72 are provided in the window 68 so that gas may leave the gas ports 52 and enter the reaction chamber 12 corresponding holes 72 in the seals 70 between the window 68 an the showerhead 26 are also be provided the seals 71 between the showerhead 26 and the housing 62 are optional and are usually not needed to obtain a good seal fig5 shows an embodiment wherein the showerhead 26 and windows 68 are a single piece eliminating the need for seals 70 and 71 in that embodiment the openings 54 which contain a portion of the housing 62 do not extend entirely through the showerhead 26 the window 68 of course must be transparent to the energy source 28 fig6 shows an embodiment wherein the window 68 includes a protective portion 74 which engages the showerhead 26 although the protective portion 74 usually will not form an airtight seal with the showerhead 26 it protects the seal 70 from a substantial amount of corrosive gases which are often present an rtp reactor 10 and which can shorten the useful life of the seal 70 in addition the vertical seals 71 between the showerhead 26 and the housing 62 shown in fig3 and 4.