Generally unstable resonators have low M2 factor but still I do not know why and I have not a physical reasons behind this. We have some profile patterns in unstable resonator like doughnut shape in hard-edged resonators, it seems in this laser configuration the M2 factor is low.
In unstable resonators with VRM (Variable Reflectivity Mirrors) we have generally low M2 factor.
Basically I am looking for the main reasons or some examples to prove this fact.
If anyone has some information such a technical note, article or book, please let me know.
Best
Kararsız bir rezonatörün M2 faktörü bulunduğu rezonans aralığına bağlıdır. Bu aralık rezonansın algılanmadığı aralıktır. Bu duruma radyasyon örneği verilebilir. Radyoaktif maddenin yayılımı sırasında herhangi sıcaklık, basınç vb. Değişkenler ölçülememektedir.
Hi
Basically the M2 parameter is refered to the purity of fundamental transverse mode in the Total content of laser beam mode population and what we know about unstable resonator is that they support very large fundamental mode and can possess almost all the gain in cavity in competition with all other higher order modes Wich causes the lase to have near diffraction limited beam quality
Ali Ebrahimi
First, thank you for your response.
Second, by a general point of view, the fundamental mode of an unstable resonator causes low M2 factor.
I am looking for some explanation based on mostly formulas, technical notes, articles or book chapters to explain why we have good beam quality in unstable resonators.
Recently I have also read somewhere that unstable resonators with hard-edged output coupler has not good beam quality.
Best
The higher the mode, the greater its losses, therefore only a certain number of the lowest modes are excited in the resonator. An unstable resonator has high losses for all modes, so only one or two “matching” the resonator geometry are excited in it. Which modes these will be, it depends on the specific geometry.
Jacek Hoffman
In unstable resonators with VRM (Variable Reflectivity Mirrors) generally,the fundamental mode operates in the resonator. I am looking for some technical notes, books or article to show mathematically why the M2 parameter of unstable resonator is low?
General formula of M2 is (M2=theta*(pi*W0)/(lambda)), so how we can prove this fact based on this formula.
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