RP Photonics logo
RP Photonics
Encyclopedia
Consulting Software Encyclopedia Buyer's Guide

Short address: rpp-con.com

Dr. Paschotta, the founder of RP Photonics, supports your R & D with his deep expertise. Save time and money with efficient support!

Short address: rpp-soft.com

Powerful simulation software for fiber lasers and amplifiers, resonator design, pulse propagation and multilayer coating design.

Short address: rpp-enc.com

The famous Encyclopedia of Laser Physics and Technology provides a wealth of high-quality scientific and technical information.

Short address: rpp-bg.com

In the RP Photonics Buyer's Guide, you easily find suppliers for photo­nics products. As a supp­lier, you can profit from enhanced entries!

Learn on lasers and photonics every day!
VL logo part of the
Virtual
Library

Slope Efficiency

<<<  |  >>>  |  Feedback

Buyer's Guide

Use the RP Photonics Buyer's Guide to find suppliers for photonics products! You will hardly find a more convenient resource.

Ask RP Photonics for advice on why the slope efficiency of your laser is lower than expected, or why the slope is not linear.

Definition: differential power efficiency of a laser

German: differenzielle Effizienz

Category: lasers

How to cite the article

An important property of an optically pumped laser is its slope efficiency (or differential efficiency), defined as the slope of the curve obtained by plotting the laser output versus the pump power (Figure 1). Usually, this curve is close to linear, so that the specification of the slope efficiency as a single number makes sense. However, nonlinear curves can occur under certain circumstances, e.g. as a consequence of quasi-three-level characteristics of the gain medium or thermal effects. For example, there can be a thermal roll-over, if the gain medium becomes hot at high pump powers, and this decreases the power conversion efficiency. A laser may even stop working for too high pump powers, for example when it leaves the stability zone of the laser resonator due to excessive thermal lensing. In case of such nonlinear curves, the slope efficiency is often determined from some approximately linear part.

threshold power and slope efficiency

Figure 1: Output versus input power for an optically pumped laser. The threshold pump power is 5 W, and the slope efficiency is 50%: each additional watt of pump power above the threshold leads to 0.5 W additional output power.

Note that the slope efficiency may be defined with respect to incident or absorbed pump power. For comparisons of power efficiency, it is usually fair to compare slope efficiencies with respect to incident powers, so that the pump absorption efficiency is taken into account. However, there are cases where values based on absorbed pump power are useful, e.g. for judging the intrinsic efficiency of the gain medium.

In simple situations, the slope efficiency is essentially determined by the product of the pump absorption efficiency, the ratio of laser to pump photon energy (→ quantum defect), the quantum efficiency of the gain medium, and the output coupling efficiency of the laser resonator.

The optimization of the laser output power for a given pump power usually involves a trade-off between high slope efficiency and low threshold pump power. The optimum is usually a situation where the pump power is a few times the threshold pump power, and the slope efficiency is reduced below the value attainable with a stronger degree of output coupling.

The slope efficiency can also be defined for other laser-like devices such as Raman lasers and optical parametric oscillators. In the latter case, the differential slope efficiency with respect to incident pump power can even well exceed 100% under certain circumstances.

See also: lasers, laser threshold, threshold pump power, output coupling efficiency, quantum efficiency, Spotlight article 2006-08-23

How do you rate this article?

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent
Comments:

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you like our website, you may also want to get our newsletters!

arrow

Field Guide on Fiber Optics

A quick introduction to fiber optics:

FG Fiber Optics

Note that we have also published a free tutorial on fiber optics!

– Show all banners –

– Get your own banner! –