Question:

A ruby laser produces radiations of wavelengths 662.6 nm in pulse duration are 10⁻⁸s. If the laser produces 0.39 J of energy per pulse, how many photons are produced in each pulse?

3.9×10¹⁸

1.3×10⁹

1.3×10¹⁸

1.3×10²⁷

Total energy of pulse, E = nhc/λ
⇒ n = Eλ/hc = 0.39 × 662.6 × 10⁻⁹ / (6.626 × 10⁻³⁴ × 3 × 10⁸) = 1.3 × 10¹⁸