A flow cytometer system is provided. The system includes a flow cell for streaming a hydro-dynamically focused liquid sample past an interrogation zone, a light source positioned to irradiate the interrogation zone with a light beam, and beam shaping optics disposed between the light source and the flow cell. The beam shaping optics manipulates the light beam and creates a horizontally flat beam profile that irradiates the liquid sample at the interrogation zone. The system includes an intermediate angle scatter (IAS) light detector positioned to measure intermediate angle scatter emitted from the liquid sample when the liquid sample is irradiated. The system further includes a mask disposed horizontally across a portion of the IAS light detector, between the flow cell and the IAS light detector, and covering at least a central portion of the IAS light detector so as to block a horizontal diffraction pattern created by the flat beam profile irradiating the liquid sample.