The optical device 1, wherein the peripheral portion is covered by {HEAD ~ the dielectric film} which has {TAIL ~ an optical thickness} of an odd multiple of λ/4, wherein λ is an oscillation wavelength 
has
The optical device 1 , wherein the peripheral portion is covered by { HEAD ~ the dielectric film } which has { TAIL ~ an optical thickness } of an odd multiple of λ/4 , wherein λ is an oscillation wavelength
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH