Slope efficiency
Encyclopedia
The slope efficiency is an important property of a laser
. It is obtained by plotting the laser output power against the input pump
power. Above the lasing threshold
, the resulting curve is usually close to a straight line. The slope efficiency is the slope
of this line. Slope efficiency can similarly be defined in terms of output and input energies instead of powers. This makes it applicable to pulsed lasers.
The curve described above is nearly linear above threshold when the optical losses in the laser cavity remain the same for all input powers. Sometimes the curve is nonlinear, typically with lower slope at high input powers. This is characteristic of increased losses, which are often thermal in nature, such as due to lensing
. This is especially common in powerful lasers.
Whatever the shape of a slope efficiency curve, it should be possible to extrapolate the line of best fit to find the intercept with the x-axis. In this way the threshold pump power
for this particular laser can be found. Determining the laser threshold periodically, via a slope efficiency graph, is particularly useful in helping to determine when a laser requires refurbishment.
The optimization of the laser output power for a given pump power usually involves a compromise between high slope efficiency and low threshold pump power.
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
. It is obtained by plotting the laser output power against the input pump
Laser pumping
Laser pumping is the act of energy transfer from an external source into the gain medium of a laser. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited...
power. Above the lasing threshold
Lasing threshold
The lasing threshold is the lowest excitation level at which a laser's output is dominated by stimulated emission rather than by spontaneous emission. Below the threshold, the laser's output power rises slowly with increasing excitation. Above threshold, the slope of power vs. excitation is orders...
, the resulting curve is usually close to a straight line. The slope efficiency is the slope
Slope
In mathematics, the slope or gradient of a line describes its steepness, incline, or grade. A higher slope value indicates a steeper incline....
of this line. Slope efficiency can similarly be defined in terms of output and input energies instead of powers. This makes it applicable to pulsed lasers.
The curve described above is nearly linear above threshold when the optical losses in the laser cavity remain the same for all input powers. Sometimes the curve is nonlinear, typically with lower slope at high input powers. This is characteristic of increased losses, which are often thermal in nature, such as due to lensing
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
. This is especially common in powerful lasers.
Whatever the shape of a slope efficiency curve, it should be possible to extrapolate the line of best fit to find the intercept with the x-axis. In this way the threshold pump power
Lasing threshold
The lasing threshold is the lowest excitation level at which a laser's output is dominated by stimulated emission rather than by spontaneous emission. Below the threshold, the laser's output power rises slowly with increasing excitation. Above threshold, the slope of power vs. excitation is orders...
for this particular laser can be found. Determining the laser threshold periodically, via a slope efficiency graph, is particularly useful in helping to determine when a laser requires refurbishment.
The optimization of the laser output power for a given pump power usually involves a compromise between high slope efficiency and low threshold pump power.