Use of a transparent lens would unavoidably create {TAIL ~ rear surface reflection} of the incoming radiation, which would mix with {HEAD ~ the sample} reflected radiation traveling toward the detector 
Use of a transparent lens would unavoidably create { TAIL ~ rear surface reflection } of the incoming radiation , which would mix with { HEAD ~ the sample } reflected radiation traveling toward the detector
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH