Question

The spacing between two adjacent longitudinal modes in a plane laser resonator having separation between two mirrors, \( d = 10 \) cm, is:

• A. \( 1000 \) MHz
• B. \( 1500 \) MHz
• C. \( 2000 \) MHz
• D. \( 3000 \) MHz

Hint:

Longitudinal mode spacing in a laser cavity depends on the mirror separation.

Answer 1

The Correct Option is C

The longitudinal mode spacing is given by:
\[ \Delta \nu = \frac{c}{2d} \] Substituting \( c = 3 \times 10^8 \) m/s and \( d = 10 \) cm = \( 0.1 \) m:
\[ \Delta \nu = \frac{3 \times 10^8}{2 \times 0.1} = \frac{3 \times 10^8}{0.2} = 1.5 \times 10^9 \text{ Hz} = 1500 \text{ MHz} \]