Why do you need low amplitude oscillation in SNOM?

[philip041]

Am I right in saying that a tapered optical fibre 'collects' light from evanscent field. Why would this mean it needs to oscillate as it scans a sample surface?

Cheers!

philip

[Gokul43201]

I would guess that the oscillation is simply to be able to lock-in detect the feedback signal.

[philip041]

I looked up lock-in detect but I don;t understand what you mean?

[f95toli]

Do you know what a lock-in amplifier is?

Lock-in detection is -in this context- basically a technique for measuring small signals (it is to some extent THE technique because it is extremely common)

[philip041]

Ah sorry. I looked up lock-in amplifier, i can see how the principle of extracting a signal from a lot of noise would be useful but I don;t get the vibrating probe thing?

Also the probe is essentially a really thin pipe? Why How does this improve resolution?

Come to think of it I have too many questions.. No worries.

[philip041]

I'm not sure but the reason it actually oscillates is to meaure transverse forces?