Maximum coherence of TEM00 modes of continuous laser radiation

The spatial (transverse) correlation function γ(s) of the field produced by a commercial cw helum–neon laser (λ = 0.633 μ) was determined with a polarizing interferometer. A high value of γ(s), decreasing toward the edge of the beam, was obtained; at 0.001 of the maximum intensity this value was γ = 0.998. The error in these measurements did not exceed 0.1%. The experimental results were analyzed using a model of superposition of completely coherent radiation on noise δ-correlated in space. The signal/noise ratio at the center of the investigated laser beam exceeded 10⁵.