Pump Conversion Efficiency basically describes the way of getting more range out of lasers using less and less power.
Optical pumping efficiency can be measured in different ways.
The overall or "wall-plug" efficiency measures what fraction of the input electrical power emerges as laser power. This is the product of several factors: power-supply efficiency, the laser diode's light-emitting efficiency, efficiency of coupling pump light into the laser medium, pump light absorption, how many pump photons stimulate emission, the quantum defect or energy difference between pump and output photon, and laser cavity. It's the usual overall measurement.
Two other efficiencies also can be useful:
- Optical-to-optical efficiency: the ratio of input pump power to output
laser power; and
- Slope efficiency: the increase of output power per unit input power
above threshold. This is the linear part of the curve in Fig. 1,
which shows how output increases linearly and then slows down before
reaching maximum output power.
FIGURE 1. Output of a laser as a function of input power, where the efficiency at any point on the curve is the input power divided by the output power and the slope efficiency measures how fast the output increases relative to the input. Normally, power increases linearly until the laser begins to saturate and then reaches a peak, as shown at the right.