# User:Pranav Rathi/Notebook/OT/2010/11/11/Small Bead Power Spectrum & DOG

### From OpenWetWare

## Power Spectrum

I have done power spectrum analysis for small bead (.5 um) first. I used more than four different beads, (4 different sets one for each); last set contains more than 1 bead. I am discussing parameters, process and the results.

### Parameters

I used AOM input voltage of 1.45 volts which corresponds to 50mW of laser power before the objective. I used low gain (step #3) on the QPD controller. All other parameters can be seen in the first few slides below. To see the slides clearly click on “view on slide share” in the lower right corner.

**Smallbeadpwsp2**

### Process & Results

I collected each set of data over a z-range of few microns. I started at the point where the trapped bead looks whitish (z=0), and went up into the sample in variable steps. The range of each step is labeled as “z=”. Each line of collected data in particular set has a z value, written before it. All four sets can be seen in the last 4 slides. The stiffness is calculated from the corner frequency in the data sheet. Data sheet also shows the z-piezo voltage and corresponding z-length into the sample away from the lower surface. The raw data can be extracted from this link:[1]