An apparatus for analyzing a population of particles is set forth. The apparatus includes an emitter adapted to generate a beam of electromagnetic radiation, such as from a laser, and a particle chamber disposed in a path of the electromagnetic radiation beam. The apparatus also includes a sensor to detect electromagnetic radiation scattered by or otherwise received from the particle chamber. A sensor alignment unit supports the sensor along a detection axis and allows adjustment of the position of the sensor along orthogonal axes lying in a plane that is generally perpendicular to the detection axis. In one embodiment, the sensor alignment unit includes a first support platform and a first adjustment mechanism disposed to adjust the position of the first support platform along a first orthogonal axis. The sensor alignment unit also includes a second support platform that supports the sensor. The second support platform is connected to the first support platform in such a manner as to allow the second support platform to move along a second orthogonal axis. A second adjustment mechanism is provided to adjust the position of the second support platform with respect to the first support platform along the second orthogonal axis. In this manner, the position of the sensor can be adjusted to optimize detection of the desired particle characteristics.