1. §16.2 夫琅和费单缝衍射
*
S
f
f ′
θ
θ
lens
lens L
·
A
B
viewing screen
a
P
O
L′
C
A slit in an opaque
obstruction
S 单色光源
θ 衍射角
缝宽ABa =
狭缝最边缘的A、B 两点发出的衍射光到达P点时的光程差
θsinaAC =
CAI
θ
λ
π
β sin
2
2 a=相应的相位差
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2. lens
f
θ
x
∆x
∆xsinθ
A slit in an opaque
obstruction
slit width a
λ
A
B
C
viewing screen
O
P
CAI
Nax =∆将缝面分割成 N 个与缝长平行的等宽窄条
每个窄条发出的子波在P点的振幅近似相等 0E∆
相邻两个窄条发出的子波在P点的相位差为
N
a
x
θ
λ
π
θ∆
λ
π
ϕ∆
sin2
sin
2 ⋅
⋅== ( N 很大 )
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4. 对于O 点: θ = 0 , ∆ϕ = 0
E0
∆E000 ∆ENE =
对于P点 :
EP < E0
lens
f
θ
x
∆x
∆xsinθ
A slit in an opaque
obstruction
slit width a
λ
A
B
C
viewing screen
O
P
ϕ∆
N →∞,N 个相接的折线将变为一个圆弧
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5. 狭缝最边缘的两窄条发出的衍射光到达 P 点时的光程差
θsinaAC =
θ
λ
π
β sin
2
2 a=
ββ 22
0Eab
R ==
βsin2REp =
lens
f
θ
x
∆x
∆xsinθ
A slit in an opaque
obstruction
slit width a
λ
A
B
C
viewing screen
O
P相应的相位差
β2
β2
β
β
sin
2
2 0E
Ep = β
β
sin0E
=
ϕ∆β N=2
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7. 1
sin
=
β
β
00 == βθ ,
λ
θπ
β
sina
=
max0 III ==
2
0
sin
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
β
β
II
lens
f
θ
x
∆x
∆xsinθ
A slit in an opaque
obstruction
slit width a
λ
A
B
C
viewing screen
O
P
(1)中央明纹中心
单缝中央主极大光强
(2)暗纹中心的位置
0sin321 ==±= βπβ L、、kk 0=I
sin
π
λ
θπ
β k
a
±== sin λθ ka ±=
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12. λ
I0
x1
x2
lens
f
θ1
viewing screen
A slit in an opaque
obstruction
0x∆
x∆
其他明纹
0
2
1
x
a
f
x ∆=≈∆
λ
sin λθ ka ±=波长对条纹宽度的影响
λ∝∆x 波长越长,条纹宽度越宽
缝宽变化对条纹的影响 CAI
a
x
1
∝∆ 缝宽越小,条纹宽度越宽
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17. L,,,kkd 210sin =±= λθ干涉明纹位置
L,,,kka 321sin =′′±= λθ衍射暗纹位置
干涉明纹出现缺级
缺级现象
干涉明纹缺级的级次
L,,,kk
a
d
k 321=′′=
ad 5= L,,,kkk 3215 =′′=
k
k
a
d
′
= 时,
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λ θ
a
d
f
透镜
I
θ
θ
衍射光相干叠加
O
P
CAI
18. §16.3 光栅衍射
大量等宽等间距的平行狭
缝(或反射面)构成的光学
元件 光栅
透射光栅
d
In one method a diamond-tipped cutting
tool is used to inscribe closely spaced
parallel lines on a glass plate, the spaces
between the lines serving as the slits.
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22. 2
sin2singl
ϕ∆
RE eP =
2
sin2
ϕ∆N
REP =
2
sin
2
sin
single ϕ∆
ϕ∆
NE
E
P
P ⋅=
22
single
sin
sinsin
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⋅⎟
⎠
⎞
⎜
⎝
⎛
=
β
β
α
α N
II OP
β
β
α
α
sin
sinsin
single
N
EO ⋅⋅=
α
αsin
singlesingle OP EE =
θ
λ
π
α sin
a
=
单缝衍射因子 多光束干涉因子
θ
λ
πϕ
β sin
2
⋅=
∆
=
d
singleOI 单缝中央主极大光强 CAI
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23. θ
λ
πϕ
β sin
2
⋅=
∆
=
d22
single
sin
sinsin
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⋅⎟
⎠
⎞
⎜
⎝
⎛
=
β
β
α
α N
II OP
θ
λ
π
α sin
a
=
πβ k±=Principal maxima occur when
主极大2
2
singlemax
sin
⎟
⎠
⎞
⎜
⎝
⎛
==
α
α
NIII OP
2
2
sin
sin
lim N
N
k
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
→ β
β
πβ 光强达极大值
λθ kd ±=sin
k = 0, 1, 2, 3, …
o
P
focal length f
viewing screen
lens
L
λ
θ
dsinθ
d
θ
multiple-slit in an
opaque obstruction
光栅方程
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πθ
λ
π
k
d
±=⋅sin
主极大