Evaporation And Research On Anti-radiation Of Bandpass Filter

A bandpass filter with a high transmittance in400-800nm band and a wide cut-offband was designed by a film structure design software named Analyst in this paper, thestructure of bandpass is double cut-off composite stucture that each side of substrate isrespectively deposited by long wave pass filter and short wave pass filter, moreover,high and low refractive index materials are respectively ZnS and MgF2.The structure and surface morphology induced by deposition temperature(50℃100℃200℃250℃300℃) of monolayer MgF2and ZnS was analized, it was foundthat each type of fim material had its prefered oriention and prefered oriention wererespectively crystal face (110) and crystal face (111). Grain side, surface roughness,area sum of surface pore, micro stress of film MgF2evaporated at250℃were not veryhigh, however, particle size and pore diameter were the smallest, taken together, thebest evaporation temperature of material MgF2was250℃; as for ZnS film, althoughparameters at250℃such as grain size, particle size, area sum of surface pore were thebiggest among other temperatures, the peak of prefered crystal face (111) was thehighest and the growth of film with prefered oriention was sacturated achiving to stablestate, therefore250℃was selected as the optimum temperature for deposition of ZnSfilm. At300℃parameters of ZnS film dropped steeply which might relate to ZnSevaporation mechanism, generally ZnS fistly decomposes Zn and S, then two kinds ofatoms combine into ZnS when depositing onto substrate.The mechanical properties of MgF2and ZnS film deposited at250℃wereevaluated according to optical coatings environmental duarability test method GB/T26331-2010, it was found that binding strength of MgF2film with substrate and wearresistence were very good, which could be deposited to the outermost layer as protectivelayer; the binding strength between ZnS layer and substrate was also very high, but itswear resistence was very poor, therefore it should be avoided to deposite ZnS film asthe outermost of the entire film system.Bandpass filter of which the transmittance spectrum was similar to theoreticalcalculation was finished on electron vaccum deposition equipment ORTUS-700at250℃which was the optimum temperature of MgF2and ZnS film material, but the width andtransmittance of bandpass still had a gap with design. Considering bandpass filter iswidely used in space, radiation test with1MeV electron was carried on, after radiationbandpass filter was colored and optical transmittance dropped, through analysis thereduction of transmittance is mainly due to substrate glass. Compared to substrate glass,anti-radiation of bandpass filter of which both sides of substrate were seperatelydeposited by long wave pass filter and short wave pass filter was improved a lot.