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The coherence time, usually designated τ, is calculated by dividing the coherence length by the phase velocity of light in a medium; approximately given by = where λ is the central wavelength of the source, Δν and Δλ is the spectral width of the source in units of frequency and wavelength respectively, and c is the speed of light in vacuum.
The equation Change in wavelength distribution as pulse widths broaden. ΔνΔt ≥ K [3] demonstrates that, for any beam shape (K), the beam bandwidth (Δν) is inversely proportional to its pulse width. Therefore, a compromise must be made to achieve maximum resolution in both the time and frequency domains.
A mode-locked laser is capable of emitting extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds.These pulses will repeat at the round trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator.
CEP in the frequency domain: The frequency spectrum of the above pulse train is a frequency comb which shows an offset if it is continued until a frequency of zero. This offset is the carrier-envelope frequency f C E O {\displaystyle f_{\mathrm {CEO} }} , and f r e p = 1 / T r e p {\displaystyle f_{\mathrm {rep} }=1/T_{\mathrm {rep} }} is the ...
FROG is currently the standard technique for measuring ultrashort laser pulses replacing an older method called autocorrelation, which only gave a rough estimate for the pulse length. FROG is simply a spectrally resolved autocorrelation, which allows the use of a phase-retrieval algorithm to retrieve the precise pulse intensity and phase vs. time.
where is the length over which the radiation pulse is amplified, is the pulse width and is the group velocity of the radiating system. [ 4 ] These conditions are much less restrictive in the relativistic limit where v c {\displaystyle {\frac {v}{c}}} is close to 1, as in a free-electron laser , compared to the usual conditions required for the ...
In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve measured between those points on the y -axis which are half the maximum amplitude.
Using this equation, the minimum pulse duration can be calculated consistent with the measured laser spectral width. For the HeNe laser with a 1.5 GHz bandwidth, the shortest Gaussian pulse consistent with this spectral width is around 300 picoseconds; for the 128 THz bandwidth Ti:sapphire laser, this spectral width corresponds to a pulse of ...