Collection by an aperture

ECE532 Biomedical Optics
Steven L. Jacques, Scott A. Prahl
Oregon Graduate Institute

An aperture is essentially a hole through which light can pass to reach some detection system.

An aperture to collect collimated light.

Consider a collimated laser beam delivering a power of 1 W to a circular 1-mm-diameter aperture. The laser beam has a Gaussian beam profile with a 1/e2 radius wo = 0.5 mm. A detector sits behind the aperture and is greater than 1 mm in diameter.

What is the power collected by the aperture?

The irradiance E [W/cm2] of the Gaussian beam profile is described as a function of the radial position r [cm] from the central axis of the beam:


The aperture presents a collection radius a = 0.5 mm. In general, the amount of power collected, Pcollected, by an aperture with radius a is:

For our case,

Pcollected = 0.632 [W]

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