## Confused about definitions in optics

The width of a pulse is typically given in the time domain, correct? The effective width is the term to describe this.

What is the spectral width in the frequency domain?

How do you calculate spectral widths and effective widths?

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From wiki:

 spectral width is the wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value. In optical communications applications, the usual method of specifying spectral width is the full width at half maximum. This is the same convention used in bandwidth, defined as the frequency range where power drops by less than half (at most −3 dB).
http://en.wikipedia.org/wiki/Spectral_width

Imagine you have a chart where the X axis runs from 500 nm to 550 nm and the Y axis is the intensity. If you plot the spectral width of a 525 nm laser you will see a very sharp peak in the center of your graph. But it's not perfectly sharp, you still have a range of wavelengths other than 525 nm. If you replaced the laser with an LED you would see much shorter, broader peak, as the LED has a wider band it emits in.

Frequency domain just means that you are plotting your graph with frequency instead of time.

Does that help?

 That helps a lot, thank you. For some reason I couldn't find that wiki article. So are frequency bandwidth and spectral width practically the same thing?

## Confused about definitions in optics

 Quote by cytochrome The width of a pulse is typically given in the time domain, correct? The effective width is the term to describe this. What is the spectral width in the frequency domain? How do you calculate spectral widths and effective widths? Thanks for your time.
In optics, a pulse is a wavepacket and during its duration the frequency of the wave may vary or not. You have to perform a Fourier transform to pass from the time domain to frequency domain or vice versa. Once you have your plot you generally measure the band width at half its intensity (full width at half maximum, FWHM)