b) illuminating the sample within {HEAD ~ said test element} with {TAIL ~ light} of NIR wavelengths, 
with
b ) illuminating the sample within { HEAD ~ said test element } with { TAIL ~ light } of NIR wavelengths ,
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH