Question

The coherence length for sodium D₂ line is 2.5cm. To deduce the coherence time and spectral width of the line. Given wavelength of D₂ line=6000 angstrom.

Answer 1

We can writer

$l=tc (1)$

where l is the coherence length, t is the coherence time, c is velocity of light in vacuum

Using (1) we get

t=8.3×10^-10 s

The spectral width of the line is given by formula

$Δλ=\frac {λ×λ}{l} (2)$

Using (2) we get

Δλ=14.4×10^-12 m

Answer

8.3×10^-10 s

14.4×10^-12 m