3- Consider a He-Ne laser radiating at spatial TEM mode, wavelength λ = 632 nm and spectral line width Aλ = 0.1nm. Beam diameter at zo =0 is w₁ = 1.0 mm. Laser resonator consists of two plane mirrors of separation L = 1.0m and assume that the reflection coefficient, R, of both mirrors is 0.99. Calculate the followings: a) What is divergence angle of beam. b) What is the beam diameter at at 1Km. c) What is the temporal coherence length of this laser. d) What is the longitudinal frequency separation. (assume refractive index n=1 inside the cavity) e) How many longitudinal modes exist under the gain curve of this laser.

3- Consider a He-Ne laser radiating at spatial TEM mode, wavelength λ = 632 nm and spectral line width Aλ = 0.1nm. Beam diameter at zo =0 is w₁ = 1.0 mm. Laser resonator consists of two plane mirrors of separation L = 1.0m and assume that the reflection coefficient, R, of both mirrors is 0.99. Calculate the followings: a) What is divergence angle of beam. b) What is the beam diameter at at 1Km. c) What is the temporal coherence length of this laser. d) What is the longitudinal frequency separation. (assume refractive index n=1 inside the cavity) e) How many longitudinal modes exist under the gain curve of this laser.