Question

What is the coherence length of the laser in vaccum if the band with of the laser is 30MHZ

Answer 1

Given:

The band width of the laser = 30 MHz

To Find:

The coherence length of the laser in vaccum

Solution:

The propagation distance over which a coherent electromagnetic wave maintains a specified degree of coherence is called coherence length.

Coherence length L is given by the formula:

$L = \frac{c}{\pi v}$

Here, c = The speed of light in vaccum = 3 X 10⁸ m/s

π = 3.14

ν = Bandwidth Frequency

We know that the SI unit of frequency is Hz and 1MHz = 10⁶ Hz

⇒ 30Hz = 3 X 10⁷ Hz

Substiuting values,

L = 3 X 10⁸ / 3.14 X 3 X 10⁷

= 10⁸ / 3.14 X 10⁷

= 10 / 3.14

= 3.18m

Hence, the coherence length of the laser in the vaccum is 3.18m.