Two common way to get coherent light Dark fringe Bright fringe Screen Double slit S1 S 1 Single slit Light source (single wavelength)
p S Chose two points on the same wave front Two common way to get coherent light
2. Constructive and destructive Interference 2丌 2丌 S: E= E10 cos(at+Pio )=E1o cos(at+pu 2丌 2丌 S2:E2=E20C0s(0+20 cos(at + p20 n,n 2丌 △p=(n20-10)-n,(nh272-nf) 士2k元 constructive k=0.1 ±(2k+1)z destructive
( ) 2 ( ) 2 2 1 1 0 20 10 = − − n r − n r destructive constructiv e k k k 0,1... (2 1) 2 = + = 2. Constructive and Destructive Interference ) 2 ) cos( 2 : cos( 1 1 0 1 1 0 1 0 1 1 1 1 0 1 0 S E E t r E t n r = + − = + − ) 2 ) cos( 2 : cos( 2 2 0 2 2 0 2 2 2 2 0 2 0 S E E t r t n r = + − = + −
jf:n0=20 ±k, constructive nii ±(k+)x, destructive s=nr Optical path length 土A入, constructive bringht δ,-8 +(k+-n, destructive dark
+ − = ) , destructive dark 2 1 ( k k , constructive bringht 2 1 = nr Optical path length 10 20 if : = + − = k destructive k constructiv e n r n r ) , 2 1 ( , 2 2 1 1
Example: find light path difference p- δ=n11-n2 6=(r1e1+n1e1)-(r2e2+n2e2 c △6=n2L-n1L L
=n1 r1- n2 r2 = (r1 -e1 +n1e1 )- (r2 -e2 +n2e2 ) s2 s1 r2 r1 n1 p n2 s2 S1p= r1 s1 p S2p= r2 = n2 L − n1 L Example: find light path difference
caution No optical path length difference through lens The various light pass through the lens would introduce no additional optical path difference or phase shift
The various light pass through the lens would introduce no additional optical path difference or phase shift. s 1 2 s No optical path length difference through lens caution: