Assuming that the sun has a diameter of 1.4 billion meters and that the rough distance between the sun and the earth is ~150 billion meters, what would you "estimate" the spatial coherence diameter on earth due to illumination from the sun? (2) Using the same sunlight, how can you increase the spatial coherence diameter that you calculated in the first question above? In other words, devise a simple method to generate even further spatial coherence from sunlight. (3) For a He-Ne (Helium-Neon) laser that has a Gaussian beam waist of 0.1 mm, what would the beam diameter be after 100 km of propagation in the air? Assume He-Ne is lasing at 633nm wavelength, which has a red color. (4) For the He-Ne laser with the given parameters in question (3), find the z distance where the radius of the curvature of the wavefront ( R(z) ) is 102 mm. (5) Briefly discuss the use and the working principles of pulsed lasers for tattoo removal and compare it to LASIK