RP Photonics logo
RP Photonics
Encyclopedia
Technical consulting services on lasers, nonlinear optics, fiber optics etc.
Profit from the knowledge and experience of a top expert!
Powerful simulation and design software.
Make computer models in order to get a comprehensive understanding of your devices!
Success comes from understanding – be it in science or in industrial development.
The famous Encyclopedia of Laser Physics and Technology – available online for free!
The ideal place for finding suppliers for many photonics products.
Advertisers: Make sure to have your products displayed here!
… combined with a great Buyer's Guide!
VLib part of the
Virtual
Library

Optical Intensity

<<<  |  >>>  |  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.

Definition: optical power per unit area

German: optische Intensität

Category: general optics

Formula symbol: I

Units: W/m2, W/cm2

How to cite the article; suggest additional literature

The optical intensity I, e.g. of a laser beam, is the optical power per unit area, which is transmitted through an imagined surface perpendicular to the propagation direction. The units of the optical intensity (or light intensity) are W/m2 or (more commonly) W/cm2. The intensity is the product of photon energy and photon flux.

For a monochromatic propagating wave, such as a plane wave or a Gaussian beam, the local intensity is related to the amplitude E of the electric field via

optical intensity from electric field

where vp is the phase velocity, c is the vacuum velocity of light, and n is the refractive index. For non-monochromatic waves, the intensity contributions of different spectral components can simply be added, if beat notes are not of interest.

Note that the above equation does not hold for arbitrary electromagnetic fields. For example, an evanescent wave may have a finite electrical amplitude while not transferring any power. The intensity should then be defined as the magnitude of the Poynting vector.

For a laser beam with a flat-top intensity profile (i.e., with a constant intensity over some area, and zero intensity outside), the intensity is simply the optical power P divided by the beam area. For a Gaussian beam with optical power P and Gaussian beam radius w, the peak intensity (on the beam axis) is

peak intensity of Gaussian beam

which is two times higher than is often assumed. The equation can be verified by integrating the intensity over the whole beam area, which must result in the total power.

In a multimode laser beam, generated in a laser where higher-order transverse resonator modes are excited, the shape of the transverse intensity profile can undergo significant changes as the relative optical phases of the modes change with time. The peak intensity can then vary, and may occur at locations at some distance from the beam axis.

The term intensity is often used in a non-quantitative or not very precise way, and not clearly distinguished from the optical power. For example, the intensity noise normally refers to noise (fluctuations) of the optical power, rather than the intensity.

Optical intensities are relevant in various situations:

Beam profilers can be used for measuring the shape of the intensity profile of a laser beam.

See also: Gaussian beams, laser beams, brightness, intensity noise, laser-induced damage

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!

If you like this article, share it with your friends and colleagues, e.g. via social media:

arrow

The Transparent Laser

The dream of each laser developer, and not only of each laser scientist: have a transparent laser, where you can look into any components and see e.g.

… and this at any location and time, with arbitrary resolution!

If you had this, finally you could

Absolutely marvelous, but only a dream?!?

Good news: such transparent lasers can be made! See our presentation:

presentation

– Show all banners –

– Get your own banner! –