A flow cytometer, laser optics assembly thereof, and methods of assembling the same are provided. The flow cytometer is capable of yielding consistent and accurate results despite exposure to adverse environmental conditions such as, for example, temperature changes within a relatively wide temperature range and/or a relatively large amount of random-axis mechanical vibration. The flow cytometer of the present disclosure is additionally or alternatively relatively insensitive to real or apparent core stream shifts, employs a slowly converging beam along the axis perpendicular to core stream flow, and provides the ability to precisely measure time-of-flight.