Github links coming soon.
The top photos consist of a wide shot of the laser apparatus itself (top) and a picture of the rubdidium resonance captured on a TV moniter (bottom). To capture the latter, we shoot the laser through a glass vapor cell (rubidium) and position a camera, which is sensitive in the infared, near the glass tube to observe the effects. When the laser frequency matches the resonant frequency of rubidium, we see the bright trail through the vapor like the shot above!
Feed-forward Current / Piezo Control Box
The goal of this is simply to vary the current given to the laser together with the piezo voltage which controls the angle of our diffraction grating in order to have more control while scanning across frequency.
The current varies inversely with frequency while the voltage given to the piezo varies proportionally. If we were very talented / lucky, we wouldn't need the control box and could instead vary the two simultaneously by hand. In order to make things easier however, we simply construct a box to do it for us. The effect is clear.
This is the current output.
This is the piezo voltage output.
For a given input voltage, the two outputs are inversely proportional to one another just like we want!
Further adjustments can be made by tuning any of the three variable resistors in the circuit above. Such adjustments will be necessary when we actually connect the box to the laser.
Another requirement of the design is for the piezo to stay postivie at all costs. This is managed by a diode connected after the op amp before the connection of the R-F resistor such that extra current can be drawn when we see a negative voltage. The proof is below.
Here is the general schematic for the op amp described in the paragraph above.
The lower signal (voltage input) has gone negative and we see the upper signal (piezo output) clipping off and not going negative. This is exactly what we want.
Even when signal is completely negative, peizo output is positive.