, . , . , , ..
, , t, , , - t + Δt , .
. () . , . . 1, , . d . . 1, d = a+b, a , b .
.
( ) ,
. , φ (φ ).
, . 2, , ( ´) , Δ:
Δ = ´´ = d sinφ (1)
( , ).
.1 . 2
, , ( d ) , , . , , , φ , ( , φ ), . (1) , ´, ., : Δ = mλ (m = 1,2,), , . φ,
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d sinφm = mλ, (2)
m = 0, 1, 2, . ( , , m = 0, φ = 0). (2)
. (2), m - φm, .
( ) , .
, , (2):
(3)
, d, m φm.
.3 , . . .
xm - m - . xm << l, , , :
, m = 1, 2, (4)