Is there any limit for generating narrow beam? How do I generate a narrow beam of 5 micron beam size?
Dear Raju,
please have a look at similar questions here on RG:
https://www.researchgate.net/post/The_minimum_spot_a_laser_beam_can_be_focused
https://www.researchgate.net/post/What_is_the_smallest_laser_focus_spot_diameter_now.
https://hds.leica-geosystems.com/hds/en/Prof_Surv_Spot_Size_Oct06.pdf
@ Ali: the question is about lateral resolution not on spectral resolution
You may get a 5 micrometer beam but at the expense of a large divergence (the beam diameter increases as a function of the propagation distance. To understand this you need to look into the ubject of gaussian beams. It is quite srightforward and very useful if you work with lasers. A perfectly collimated beam really does not exist. Rather than that what you can obtain is a laser that focuses into a waist, at which it is collimated and then it diverges again. The angle at which the beam spreads from the waist is called the divergence angle. The narrower the waist, the larger the divergence angle. Divergence_angle=2*lambda/(Pi*w0). w0 is the beam radius at the waist. This formula is approximate and is valid far from the waist where the divergence is linear with propagation distance.
I recommend you grab any book on optics that has a chapter on gaussian optics to read this subject. It is very interesting.
I would add the wikipedia page on gaussian beam propagation: https://en.wikipedia.org/wiki/Gaussian_beam
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