# Questions regarding OPA and TPA techniques

valisd

The attached pdf file is the paper im reading, there are several points in this paper that i havent understood

Question 1: In the "Introduction" section (second paragraph), they claim that strong linear absorption in the OPA technique makes this only usable for 2D scanning and the absence of linear absorption in TPA technique and local non-linear absorption makes this technique applicable for 3D scanning. Please explain and elaborate this idea with graph and/or equation.

Question 2: In the "Working principle of LOPA microscopy" section, they wrote: "The intensity increases nonlinearly and reaches a maximum value at the focal plane " (line 2 and 3). Please explain and elaborate this idea with drawing and/or equation.

Question 3: In the "Working principle of LOPA microscopy" section, from line 1 to 6 at page 4, they imply that the high absorption of OPA decreases the intensity of light and this is a disadvantage of OPA technique and it hinders the the OPA technique from achieving what the TPA technique can do (being able to give off light with high intensity and get photo induced effect). However, at line 8 to 11 they claimed that the strong linear absorption of OPA technique can also get photo induced effect ? Can you elaborate on this idea ? i think im misunderstanding something

Question 4: In the "Working principle of LOPA microscopy" section, paragraph 2 (from line 12 page 4). They are explaining on how they get low absorption effect with OPA. I don't understand this at all. Can you explain this with drawing and/or equation ? thank you.

Question 5: In the "Working principle of LOPA microscopy" section, paragraph 2, line 7 to 9 they wrote " Although the absorption is ultra weak, the effective photo induced effect in focusing region is therefore comparable to that obtained by a laser beam with a high absorption effect". I do not understand this point at all because i thought the whole point of this is making OPA having low absorption like the TPA technique so this OPA technique can do what the TPA technique can too. Why are they speaking of the "high absorption effect" as an advantage now ? What am i misunderstanding

• 4 months ago
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