定义：
脉宽是其光谱能支持的最短脉宽的脉冲串。

带宽极限脉冲也叫变换极限脉冲（transform-limited pulse）或者傅里叶变化极限脉冲（Fourier-transform-limited pulse），其脉宽是相同光谱下的最小值。这也就是说，该脉冲的时间带宽积达到了最小值。例如：对于双曲正割型脉冲，其最小的时间带宽积为0.315，这也就意味着对于一个脉宽为100fs的双曲正割型脉冲，其至少应当具有3.15THz的带宽。 
另一个相近似的定义为：在给定的脉冲能量下，带宽极限脉冲的峰值功率是其光谱所能支持的最大峰值功率。这也就意味着该脉冲的谱相位是一条直线，并且通常也意味着最短的脉冲宽度。 

图 1：中心分别在1mm和1.5mm的双曲正割型（sech2-shaped）的带宽极限脉冲在不同的谱宽情况下对应的脉宽 
当一个带宽极限脉冲通过介质后，其时间带宽积会由于色散或者非线性的作用而逐渐变大。色散的作用会使得时域上的脉冲宽度变宽但是光谱宽度并不会变化，也就是说该脉冲变成一个啁啾脉冲。其啁啾可以利用色散补偿器件进行脉冲压缩来移除，从而恢复到原有的脉冲宽度。而非线性的作用则会展宽其光谱。 
许多锁模激光器，特别是孤子锁模型的固体激光器和一些锁模二极管激光器，可以产生近似的带宽极限脉冲。带宽极限脉冲的特性是很有用的，比如在光纤通信中，其可以使色散导致的时域展宽最小化。

Definition: pulses with a duration as short as possible with their optical spectrum

Alternative term: transform-limited pulses

A bandwidth-limited light pulse (or transform-limited pulse) is a pulse which is as short as its spectral bandwidth permits. In other words, its time–bandwidth product is as small as possible for a given temporal or spectral shape For example, the minimum time–bandwidth product of sech²-shaped pulses (calculated with the full width at half-maximum both in time and frequency domain) is 0.315, which implies that bandwidth-limited sech² pulses with a duration of 100 fs must have a bandwidth of 3.15 THz.

Note that the considered spectral bandwidth is related to the Fourier transform of the electric field. That bandwidth is necessarily large when the pulses are very short; that is due to the basic mathematical properties of Fourier transforms [1], i.e., not related to any physical processes e.g. of the used pulse generation mechanism.

A slightly different definition for a bandwidth-limited pulse is that its peak power is as high as the optical bandwidth allows (for a given pulse energy). This is equivalent to the pulse having a flat spectral phase, but does not always precisely lead to the shortest possible pulse duration in terms of full width at half maximum.

Figure 1: Optical bandwidth of sech²-shaped bandwidth-limited pulses. Different curves apply for different center wavelengths due to the conversion from frequency to wavelength intervals.

If an initially transform-limited pulse propagates through a medium, its time–bandwidth product can increase due to the influences of chromatic dispersion or nonlinearities. For example, the influence of dispersion can temporally stretch the pulse while leaving its spectral width constant. This is associated with a chirp. This chirp can later be removed by dispersive pulse compression, restoring the original pulse duration.

Many mode-locked lasers, particularly soliton mode-locked solid-state lasers, but also some mode-locked diode lasers, can generate nearly bandwidth-limited pulses. This feature is very desirable e.g. in optical fiber communications, as it minimizes dispersive temporal broadening.

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