Right now I am working with: PMT: Hamamatsu R928/0115/0381 PMT Power Supply: McPherson PMT Power Supply Model # 7640 O-Scope: Tektronix TDS 5104 Oscilloscope PMT Housing: PhotoCool Housing PMT Housing Power Supply: PhotoCool Power Supply Input: 200 mW 532 nm ND:YAG laser I have pictures uploaded but I cannot post them until I have 15 posts. Sigh. Here is the problem: We are selecting the wavelength through a monochromator. We have the wavelength of the monochromator set to 533NM. We have been able to see some signal from this wavelength setting on the monochromator in the past. So, with a shutter, I took a picture of the waveform with no laser and with laser. Both tests were performed at 935 volts. The first picture shows a normal amount of noise. The second picture however, with the ND:YAG, has a huge dip and then levels off. The noise disappears in this second waveform. This distortion is repeatable, but has been intermitent. Saturation has been suggested. It does not seem entirely possibly but right now because of the monochromator, but the current plan is to ND filter the laser and see if any noticeable difference occurs. I also have a chopper lined up to attempt to properly generate a useable signal. Anyone have any other suggestions on what may be causing distortion with this PMT setup?