The laser assembly subsystem will have most of the losses that we must pay very close attention to. The first step will be taking power from the wall-plug and then conditioning that power to be of the type needed by whatever the pump source is. This might require transformers, pulse-forming circuits, and other complex electrical systems that will inherently have power losses with each conversion from one power form to another. The power conditioning subsystem will have an efficiency associated with it we will define as η Pconv.

Once the power is converted to a form the pump source can use, it must be coupled into the pump system. The power coupling from the power conditioning subsystem to the pump source is typically done through some type of electrical connectivity, which will vary based on the power format.

For high-voltage pulsed system low-loss, low-inductance high-voltage cables are required. For CW lasers the power is typically direct current high voltage so the cables must be low loss and low capacitance. Whatever the system is, there will also be some losses in the process of coupling electrical power from the power conditioning subsystem to the pump source. We will define the efficiency of coupling power here as η Pcoup.

At this point, we have power delivered to the pump source and the pump source must convert the electrical power to a form that can be absorbed by the active medium. This might be done by dumping all the power into a flash lamp and creating an optical flash of light. The power could be used to drive laser diodes to pump the active medium. Like in the case of the HeNe the power might be delivered directly into the medium gas to create a plasma discharge. Whatever the pumping mechanism may be, there will be an efficiency of delivering that pump power into the gain medium. In the case of the flashlamp some of the light from the optical flash will be reflected off the surface of the active medium and will be lost. Some of the light might be absorbed by impurities in the host material and converted to heat. In the case of a gas laser, some of the energy is lost in ionizing the gas molecules and again some is lost in unwanted transitions that are de-excited through transferring heat to the walls of the container. Again, there is an efficiency of supplying pump power into the active medium we will call η pump.