I am working on building a QEPAS setup. I am using HHL-513 as laser and ADM01 from Thorlabs. Inside the ADM01, there is a QTF(Quartz Tuning Fork). Basically, for the setup to work, what we have to do is to make sure the laser passes through the ADM01 and it also should go between the QTF prongs. The gas molecules present in the ADM01 will vibrate because of the laser and in turn it vibrates the QTF and from that only we get the electrical signal output. So for proper alignment of the laser and ADM01, I kept the ADM01 in between the laser and a photodetector. So if we get a photodetector signal output, we can be sure that laser passes through the ADM01.
The problem was that I was getting photodetector output signal but I was getting only noise from the ADM01.Now since the laser is not visible, we have to use a laser viewing card to make the proper alignment. So while doing that, the card blocks the laser for some time and during that the photodetector output vanishes, which is what should happen but the noise which I am getting from the ADM01 is same irrespective of the laser being blocked or passing through the ADM01.So probably, there is some problem in the output circuit of ADM01.I have also attached the image of the output circuit. The red is positive, violet negative, black ground and the green should give the output signal. To power the circuit, I have used two 12V adapters. Can you tell if there is something wrong in the output circuit?
