I need to design some beam shaping optics to control the divergences of R, G, and B laser beams to make three color holograms. For that I need to know the virtual point source of where the beams originate to do the geometric ray-tracing.
Beam diameter as given in manufacturers spec’s is measured at the output aperture, correct? And if the beam has a given divergence, then it should be simple enough trigonometrically to find the tip of the triangle, no? Here are some examples of my homework.
For example, my Coherent Compass 315M has a divergence of < 2.2 mrad, and diameter of .32 mm. Constructing an isosceles triangle with a base of .32 mm and apex angle of 2.2 mrad gives a height of 145 mm, which should mean that the virtual point source I am looking for is 145 mm behind the output end of the laser. (Breaking the isosceles into two right triangles, each with a base of .16 mm and an angle opposite that of 1.1 mrad yields the 145 mm distance.)
My Lasos RLK 40200 TS has a divergence of 1.4 mrad, and diameter of .7 mm. Following the same reasoning I get the virtual point source 1 meter behind the laser.
And my Melles Griot BLD 605 with its funky elliptical beam has two divergences and dimensions, but I need to only get the narrow side to coincide with the other two’s dimensions, so its .15 mm wide beam and < 5 mrad divergence places its virtual source 60 mm behind the output window.
This is probably way too simplistic, as diffraction plays into forming a beam waist, but at least it could be a starting point in doing the geometric ray tracing to make some beam shaping telescopes. Anybody see any flaws in my reasoning? Is this how you guys cipher (to use a Jethro-ism) for same sized beams in laser light shows?