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Power Step-Up Beam Profile experiment (BPE)
Correct beam profile is very important for optical trap; in our case its (0, 0) Gaussian mode. It looks like that at higher powers our laser moves to higher modes, which introduces some extra difficulties in focusing at getting diffraction limited spot size, and not good for the stiffness calibration. The motivation behind doing this experiment is to answer some questions.
Answering the following questions. 1) At what output power the beam profile starts changing? 2) Is this change slow with power? 3) How much does it change at 4.1W in comparison to the power-point at; it just starts changing? 4) What is the appropriate range of power for tweezing?
The profiling is done from .2W to 4.1W in .3W steps at 85 deg F, laser temperature. The beam was passed through AOM (AOM at CW mode) and 2nd order diffracted beam was picked for profiling. The profiling is done through a regular CCD camera with following set-up:
Just by looking the pictures, it is clear; what happens to the beam at higher powers and up-to what power the beam stays in the fundamental mode.